New Oxyhalide Solid Electrolytes with Enhanced Conductivity for All-Solid-State Batteries.

Open AccessCCS ChemistryRESEARCH ARTICLE1 May 2022Boosting Efficient Ammonia Synthesis over Atomically Dispersed Co-Based Catalyst via the Modulation of Geometric and Electronic Structures Yanliang Zhou†, Congying Wang†, Xuanbei Peng†, Tianhua Zhang, Xiuyun Wang, Yafei Jiang, Haifeng Qi, Lirong Zheng, Jianxin Lin and Lilong Jiang Yanliang Zhou† National Engineering Research Center of Chemical Fertilizer Catalyst, Fuzhou University, Fuzhou, Fujian 350002 , Congying Wang† National Engineering Research Center of Chemical Fertilizer Catalyst, Fuzhou University, Fuzhou, Fujian 350002 , Xuanbei Peng† National Engineering Research Center of Chemical Fertilizer Catalyst, Fuzhou University, Fuzhou, Fujian 350002 , Tianhua Zhang National Engineering Research Center of Chemical Fertilizer Catalyst, Fuzhou University, Fuzhou, Fujian 350002 , Xiuyun Wang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] National Engineering Research Center of Chemical Fertilizer Catalyst, Fuzhou University, Fuzhou, Fujian 350002 , Yafei Jiang Department of Chemistry, Southern University of Science and Technology, Shenzhen 518055 , Haifeng Qi Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023 , Lirong Zheng Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 , Jianxin Lin National Engineering Research Center of Chemical Fertilizer Catalyst, Fuzhou University, Fuzhou, Fujian 350002 and Lilong Jiang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] National Engineering Research Center of Chemical Fertilizer Catalyst, Fuzhou University, Fuzhou, Fujian 350002 https://doi.org/10.31635/ccschem.021.202100912 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Ammonia (NH3) synthesis at mild conditions is of great significance, while the significant bottleneck of this process is the activation of N2 to realize the desired NH3 synthesis performance, which requires deep insight and rational design of active sites at the atomic level. Here, were synthesized atomically dispersed Co-based catalysts with different Co-N coordination numbers (CNs) to explore the coordination-sensitive NH3 synthesis reaction for the first time. Our studies showed that Co-based catalysts increased the NH3 synthesis rate gradually with a decrease in CN. The Co-N2 catalyst exhibited the highest NH3 synthesis rate of 85.3 mmol gCo−1 h−1 at 300 °C and 1 MPa, which outperformed most of the previously reported Co-based catalysts. Various characterizations and theoretical calculations demonstrated that atomically dispersed Co catalyst with low CN could generate more unoccupied Co 3d charges and tetrahedral cobalt(II) sites. The unoccupied Co 3d charge, in turn, promoted the electron donation from the Co active center to the antibonding π-orbital (π*) of N2 and expedites N2 hydrogenation. Furthermore, the Co-N2 catalyst with more tetrahedral cobalt(II) sites could effectively facilitate the desorption of N-containing intermediate species (such as *NH3 and *N2H4) to obtain a high NH3 synthesis rate. Download figure Download PowerPoint Introduction Ammonia (NH3) is not only an essential raw material for the synthesis of nitric acid, fertilizer, ammonium salt, and so on but also a promising renewable energy carrier.1,2 The state-of-the-art manufacture of NH3 comes from the Haber–Bosch (HB) process using iron-based catalysts that require harsh reaction conditions (400–500 °C, 10–30 MPa), thereby suffering from high energy consumption and environmental pollution problems.3–5 Therefore, it is urgent to develop effective routes that are both energy-saving and environment-friendly. Most recently, electric power generated from renewable energy sources is widely used for hydrogen (H2) production via water electrolysis. It becomes economically acceptable to NH3 synthesis from renewable H2 and N2 via an electrolysis-driven HB (eHB) process.6 The eHB route is attractive for realizing efficient utilization of renewable energy and a "carbon-free" society. However, the major challenge of NH3 synthesis lies in the activation of N2 (945 kJ mol−1) at mild conditions to realize desired NH3 synthesis rate,7 which would require a deep insight into the reaction mechanism; therefore, the development of advanced, efficient catalysts that can produce NH3 at mild conditions is beneficial. Currently, industrial applied Fe- or Ru-based catalysts that exist as nanoparticles usually obey the dissociative mechanism,8,9 requiring harsh conditions to dissociate the stable N≡N triple bond. In contrast to the N2 dissociative mechanism, most of the enzyme-catalyzed N2 fixation processes followed the associative mechanism, wherein the N≡N triple bond breaks stepwise after partial hydrogenation of the N2 molecule.10,11 Notably, the dissociation energy of the N–N bond (297 kJ/mol) from *N2H4 intermediates is less than a third of that from the N≡N triple bond. Consequently, the exploitation of advanced catalysts that obey the N2 hydrogenation process instead of direct N2 dissociation is promising for realizing the desired NH3 synthesis performance at mild conditions. Further, NH3 synthesis is a typical structure sensitivity reaction, where the pathway of N2 activation is closely related to the geometric and electronic structures of active sites.8,12 For instance, theoretical studies have demonstrated that N2 could preferentially undergo hydrogenation via an associative pathway other than direct dissociation on Ru(0001) surface,13 RhCo3 clusters,12 and Co3Mo3N catalysts.14 In addition, very recently, a limited number of researches have provided us with experimental evidence that the N2 hydrogenation to N2Hx species is preferred over atomically dispersed Ru and Co, as well as Li-promoted Ru catalysts.6,15,16 Among them, atomically dispersed catalysts present well, having the potential for NH3 synthesis at mild conditions, as the direct N2 dissociation is difficult while the N2 hydrogenation is feasible on single-atom sites.15 Meanwhile, atomically dispersed catalysts with definite structures offer the possibility to investigate the geometric and electronic effects on NH3 synthesis at the atomic level. Differing from nanoparticle catalysts, in which the particle size and crystal face usually play an important part in the reactivity, catalytic activity of atomically dispersed catalysts is mainly determined by the coordination environment of single-atom sites.17–19 However, up to now, the modulation of the coordination structure of single-atom active sites to optimize the catalytic activity of NH3 synthesis has not yet been researched. Moreover, the effects of geometric and electronic structures in these single-atom sites on the dynamic transformation of intermediates remain unclear. Herein, we synthesized a series of atomically dispersed Co-Nx (x = 2∼4) catalysts through the pyrolysis of nitrogen-anchored Co-based precursors. The coordination numbers (CNs) of Co-N over the as-prepared catalysts were modulated by varying the calcination temperature. The coordination-sensitive NH3 synthesis reaction in the case of Co-based catalyst is disclosed through a combination of a suite of elaborated experimental characterizations and theoretical calculations. The geometric and electronic structures of Co active sites could be simultaneously tuned via the modulation of Co-N CNs, which are closely related to the N2 activation and desorption of N-containing intermediate species (such as *N2H4 and *NH3), thus resulting in different catalytic behaviors in the NH3 synthesis. This finding is beneficial to rationally design advanced Co-based catalysts by regulating the geometric and electronic structures to realize efficient NH3 synthesis at mild conditions. Experimental Methods Catalyst preparation Synthesis of hollow N-doped porous carbon spheres support The synthetic method of hollow N-doped porous carbon spheres (HNPCSs) support was referenced in previous work.20 Briefly, NH3 solution (10 mL) and ethanol (240 mL) were dissolved in deionized water (80 mL) and stirred evenly at room temperature (RT). Then, tetraethyl orthosilicate (11.2 mL) was added to this solution and stirred further for 1 h. Subsequently, poloxamer, resorcinol, and formaldehyde (2.24 mL) were added to the above solution and continually stirred for 0.5 h. After the addition of melamine (1.26 g) and formaldehyde (1.68 mL), the mixture was treated at 100 °C for 24 h. After filtration and washing, the sample obtained was calcined under an Ar atmosphere at 700 °C for 2 h. Finally, the sample was etched by hydrofluoric acid (HF) solution to remove the SiO2 substrate. After filtration, washing, and drying, the resulting substance was herein referred to as HNPCSs support. Synthesis of Co-Nx and Co-NPs catalysts In detail, HNPCSs (120 mg) and cobalt phthalocyanine (CoPc; 80 mg) was dispersed in dimethylformamide (DMF; 120 mL), respectively, and the mixtures were stirred for 2 h. Then the CoPc and DMF mixed solution was added slowly to the HNPCSs suspension. After stirring for 24 h, the sample was dried in a vacuum dryer at 60 °C for 12 h. Finally, the samples were pyrolyzed under Ar atmosphere at different temperatures of 450, 550, and 650 °C for 2 h, denoted as Co-N4, Co-N3, and Co-N2, respectively. The synthetic procedure used for the Co-NPs catalyst was similar to that of Co-N2, except that the calcination was performed at 700 °C for 10 h. Synthesis of catalysts as reference The Cs-Co/MgO catalyst was synthesized by an impregnation method. In detail, a certain amount of cobalt nitrate hexahydrate and cesium nitrate was dissolved in deionized water. MgO support was added to this solution, and the mixture was stirred evenly. After impregnation at RT for 24 h, the mixture was dried at 80 °C for 24 h. The acquired catalyst was denoted as Cs-Co/MgO, in which the content of Co was the same as that over Co-N2, and the molar ratio of Cs to Co was ∼1.0. A Fe-based catalyst was purchased commercially from Fujian SJ. FD. Co. Ltd. (Fuzhou, Fujian, China) for comparative studies. NH3 synthesis performance test The NH3 synthesis activities over the as-synthesized catalysts were tested in a pressurized fixed bed reactor. In detail, the catalyst (0.2 g, 20–30 mesh) was loaded into the stainless steel reactor (inner diameter 10 mm). Before measurement, the catalysts were treated in a 25%N2–75%H2 feed gas at 300 °C for 2 h. Subsequently, the catalyst performance was evaluated in 300 °C at a weight hourly space velocity (WHSV) of 60,000 mL g−1 h−1 and 1 MPa. The outlet NH3 was trapped by diluted H2SO4 solution and then detected by ion chromatography (DIONEX, ICS-600; Thermo Scientific, Waltham, MA, USA). The turnover frequency (TOFCo) was calculated based on the total molar of Co metal using the following equation: TOF Co = r n M (1)where, r represents the NH3 synthesis rate (mol g−1 s−1), nM is the molar amounts of Co obtained from inductively coupled plasma (ICP) analysis. Catalyst characterization X-ray diffraction (XRD) measurement was recorded on a PANalytical X'Pert Pro diffractometer (PANalytical, Almelo, The Netherlands) using a Cu Kα radiation source. N2 adsorption/desorption isotherms were collected on an ASAP 2020 apparatus (MicroMetric, Lincolnshire, United Kingdom). Elemental analysis (EA) was conducted with a Vario EL-Cube instrument (Elementar, Jiangsu, China) to measure the N contents of the samples. The Co contents of the catalysts were measured by ICP atomic emission spectroscopy (ICP-AES) analysis equipped with an Ultima 2 spectrometer (Perkin-Elmer, Waltham, MA, USA). Catalyst morphologies were detected on scanning electron microscopy (SEM; a Hitachi Model S-4800; Hitachi, Tokyo, Japan). Transmission electron microscopy (TEM) images of the catalysts were obtained on a JEM-2010 instrument (JEOL Ltd., Tokyo, Japan). Aberration-corrected high-angle annular dark-field scanning TEM (AC-HAADF-STEM) analysis was performed on a JEOL JEM-ARM 200 F instrument (JEOL Ltd., Tokyo, Japan). Raman spectroscopy was measured on a multichannel modular triple Raman system (Renishaw Co., London, United Kingdom). Ultraviolet photoelectron spectroscopy (UPS) was measured using a helium resonance lamp offering He I (hν = 21.2 eV) photons. X-ray photoelectron spectroscopy (XPS) was performed on an ESCALAB 250Xi photoelectron spectrometer (Thermo Fisher Scientific, Shanghai, China) with a monochromatic Al Kα source (hν = 1486.6 eV) as the X-ray source. The XPS binding energy was referenced to the C 1s peak at 284.6 eV of adventitious carbon. Electron-paramagnetic resonance (EPR) test was performed on an E500 spectrometer (Bruker-BioSpin, Shanghai, China) with a 100 KHz magnetic field modulation at RT. UV–vis diffuse reflection spectrum (DRS) data were obtained from a Perkin Elmer Lambda 750s UV–vis spectrometer (Perkin-Elmer, Waltham, MA, USA). The productions of NH3 synthesis were trapped at the aqueous solution containing sulfuric acid and para-(dimethylamino) benzaldehyde for the UV–vis DRS measurement. X-ray absorption spectroscopy (XAS), containing X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses were performed at the 1W1B beamline of the Beijing Synchrotron Radiation Facility (BSRF), China. Spectra were collected at the Co K-edge in transmission mode with a Si (111) double crystal monochromator. The Co foil and CoPc samples were used as references. Density functional theory (DFT) calculations First-principle calculations were performed using the generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof (PBE),21 as implemented in the Vienna ab initio Simulation Package (VASP 5.4.4).22 The valence electronic states of all atoms were expanded in a plane-wave basis set with a cutoff energy of 400 eV, and gamma points were used for Brillouin zone integration. All atoms were allowed to relax until the forces fell below 0.02 eV Å−1. The energy convergence criterion was set to 10−5 eV. Grimme D3 method with the zero-damping function was used to describe van der Waals interactions.23 The graphene supercell with a surface periodicity of 10 × 10, including 200 atoms as a basis, was employed to construct the Co-Nx (x = 4, 3, and 2) moieties. A vacuum space of 20 Å was used in the normal direction of the graphene plane to ensure negligible interaction between the mirror images. Results and Discussion Structure characterization The process for the synthesis of Co-Nx catalysts with different Co-N CNs is depicted in Figure 1a. The atomically dispersed Co-Nx catalysts were prepared by CoPc pyrolysis supported on HNPCSs precursor. The CN of Co-Nx catalysts was modulated by varying the pyrolysis temperature (as shown in the "Catalyst preparation" section). To highlight the coordination structure of atomically dispersed Co center, Co nanoparticle loaded on the same support (Co-NPs) was prepared for comparison. EXAFS analyses of the Co K-edge were conducted to demonstrate the coordination structure of Co-Nx catalysts. The Co K-edge EXAFS spectra of as-synthesized catalysts and reference Co foil and CoPc, are illustrated in Figure 1b. An apparent peak located at 1.5 Å for the as-synthesized Co-Nx samples was attributed to Co-N coordination, compared with CoPc reference.24 Meanwhile, no typical peaks for Co-Co coordination at 2.2 Å were visible, indicating the atomically dispersed Co atoms on these Co-Nx catalysts. Besides, the peak intensity of Co-N coordination decreased with increased pyrolysis temperature, suggesting a decrease in Co-N CN. Based on fitting results, the average CNs of Co-N of the three samples were 3.9, 3.0, and 2.1 (Table 1), and thus, the samples were denoted as Co-N4, Co-N3, and Co-N2, respectively. Additionally, the fitting result of Co K-edge EXAFS spectra of Co-N2 based on our hypothetical model was consistent with the experimental result (Figure 1c), demonstrating the validity of the depicted models. In the case of Co-NPs, the Co-Co coordination existed predominant beside the weak Co-N coordination, indicating that Co entities were distributed mainly in the form of nanoparticles. Figure 1 | (a) Schematic diagram of the preparation process of Co-Nx with different CNs. (b) Co K-edge EXAFS spectra of as-prepared samples. (c) EXAFS spectra and the corresponding curve-fitting results of Co-N2 catalyst. Download figure Download PowerPoint Table 1 | EXAFS Data Fitting Results of the As-Synthesized Catalysts Samples Shell CN R (Å)a σ2 × 102 (Å2)b ΔE0 (eV)c R-Factor (%) Co foil Co-Co 12.0 2.49 0.7 6.3 0.9 Co-N4 Co-N 3.9 1.92 0.4 8.1 0.07 Co-N3 Co-N 3.0 1.91 0.3 7.2 0.09 Co-N2 Co-N 2.1 1.89 0.3 −1.1 0.8 Co-NPs Co-N 2.0 2.03 0.7 −1.8 0.7 Co-Co 2.1 2.49 0.7 −1.8 0.7 Note: The accuracy of parameters: CN, ±20%; R, ±1%; σ2, ±20%; ΔE0, ±10%. The fitting range in k- and R-space is 3.0–12.3 Å−1 and 1.0–2.7 Å, respectively. aR, bonding distance. bσ2, the Debye–Waller factor. cΔE0, inner potential shift. SEM ( Supporting Information Figure S1) and TEM images (Figures 2a and 2b) simultaneously displayed uniform microspheres with the hollow structure of Co-Nx and Co-NPs catalysts. The average diameter of the microspheres was ∼150 nm of these samples. The high-resolution TEM (HR-TEM) images (Figure 2c and Supporting Information Figure S2) did not show any Co nanoparticles sights, implying a high dispersion of Co species as clusters or single atoms over Co-Nx catalysts. We further used the AC-HAADF-STEM characterization to inspect the Co species over Co-Nx catalysts. We found that plenty of highly dispersed Co single atoms were visible over Co-N2 (Figure 2d), Co-N3 (Figure 2e), and Co-N4 (Figure 2f) catalysts. In comparison with Co-Nx catalysts, distinct nanoparticles were observed over the Co-NPs catalyst ( Supporting Information Figure S3). Combined with the EXAFS results, we deduced that atomically dispersed Co-Nx catalysts with different Co-N CNs were synthesized successfully. Figure 2 | (a and b) TEM and (c) HR-TEM images of Co-N2 catalyst. AC-HAADF-STEM images of (d) Co-N2, (e) Co-N3, and (f) Co-N4 catalysts. Download figure Download PowerPoint The XRD patterns ( Supporting Information Figure S4) showed that all Co-Nx displayed a broad diffraction peak at ∼26.4°, to the crystal plane of carbon The highly was by Raman measurement. The Raman spectra ( Supporting Information Figure displayed that samples peaks at and corresponding to the and of or carbon and Furthermore, the intensity of the to of these samples were ( Supporting Information Table that the coordination structure has a on carbon Notably, the diffraction peaks on the Co-N4 sample are attributed to the CoPc suggesting an of CoPc species and the of Co-N4 which with the fitting results of XRD diffraction peaks were related to Co or CoPc species in the Co-N3 and Co-N2 samples. to the above EXAFS and our demonstrated that the pyrolysis of CoPc would form atomically dispersed Co sites over Co-Nx catalysts after the pyrolysis of the at 700 °C for 10 h, the of diffraction peaks at and in Co-NPs catalyst were to the (111) and crystal of Co respectively. The average size of Co nanoparticles over Co-NPs was to the of (111) crystal plane via which with the particle observed in the HR-TEM ( Supporting Information Figure S3). showed that the Co contents in these samples were distributed in the range of ( Supporting Information Table to the results, the N contents of the synthesized Co catalysts ( Supporting Information Table S1) decreased with increased pyrolysis temperature. N2 ( Supporting Information Table S1) results showed that the surface of Co-Nx catalysts increased from to g−1 with increased pyrolysis temperature. However, at a high pyrolysis temperature, the surface of Co-NPs catalyst decreased to of the geometric and electronic structure was performed to insight into the of different CNs on the geometric and electronic structure of Co sites. to the results (Figure the peak intensity in the range of eV was of the geometric of Co that tetrahedral or The from the tetrahedral of Co sites were to to this The intensity of this peak over Co-N2 was than that of Co-N3 or Co-N4, indicating that more Co were at the tetrahedral sites in the Co-N2 Besides, the of the absorption in the images (Figure could be used to the states of Co A of absorption from Co-N4 to Co-N2 was indicating that the valence of Co species decreased with decreased CN of the Co-Nx catalysts. Figure | Co K-edge spectra and the images in the range of (a) eV and (b) eV. Download figure Download PowerPoint Further, XPS were performed to obtain the valence of Co and N species over the as-synthesized catalysts. shown in Figure the Co spectra were fitting into the peaks with binding of and eV, to and peaks of surface Co were observed on these catalysts, except for Co-NPs, which with the results of XRD and The atomic ratio of over the Co-N4, Co-N3, and Co-N2 catalysts determined from XPS results were and (Table This finding was supported by the of Co entities over Co-N2 as shown in the (Figure results, that the decreased CN have been promoted to generate more unoccupied Co 3d over the Co-N2 results were further by The spectra ( Supporting Information Figure showed that the of and over these catalysts were attributed to an electron in the of and carbon We found that the intensity of increased with the of CN, indicating that more on the Co-N2 catalyst. The N 1s spectra (Figure three of N and N over Co-Nx the comparison of the content of different N species from the peak (Table we observed that the N content increased from to while the N content decreased from to with of CN over Co-Nx catalysts. This result that the atomically dispersed Co mainly with the these demonstrated that the geometric and electronic structures of the atomically dispersed Co catalyst were modulated through different CNs of the in turn, the catalytic activity the NH3 synthesis. Figure | (a) Co and (b) N 1s XPS spectra of the as-synthesized catalysts. Download figure Download PowerPoint Table 2 | The XPS Spectra Results of the As-Synthesized Catalysts Samples N (%) N (%) N (%) (%) (%) (%) Co-N4 24 60 Co-N3 12 Co-N2 20 Co Catalyst activity and Figure the NH3 synthesis rate over the as-synthesized catalysts with a 25%N2–75%H2 gas and a of mL The NH3 synthesis rate in the case of Co-N2 was 85.3 gCo−1 h−1 at mild conditions of 300 °C and 1 MPa, than over Co-N3 gCo−1 and Co-N4 gCo−1 An NH3 synthesis rate of gCo−1 h−1 was acquired over Co-NPs, which is more to over the atomically dispersed Co-Nx catalysts. Meanwhile, the NH3 synthesis rate over the carbon as support was mmol h−1 at 300 °C and 1 MPa, as shown in Supporting Information Table suggesting that the of support to the catalytic activity of Co-Nx could be results that NH3 synthesis is a coordination-sensitive reaction, and the Co-N2 catalyst with the CN the highest NH3 synthesis rate at mild conditions. It has been reported that the addition of a electronic to Co-based catalysts could NH3 synthesis performance, referred to as an electronic Herein, we the of to the highly active Co-N2 catalyst on NH3 synthesis It showed that the NH3 synthesis rate over was that of the (Figure The typical Cs-Co/MgO and the Fe-based catalysts were also performed and evaluated for comparison ( Supporting Information Table 300 °C and 1 MPa, the NH3 synthesis rate over Co-N2 mmol gCo−1 was than of Cs-Co/MgO mmol and Fe-based mmol catalysts, indicating the performance of NH3 synthesis activity over Co-N2 catalyst. For based on the total number of Co active sites on these catalysts, were calculated and depicted in Figure Notably, the of Co-N2 and were and respectively, which outperformed most of the previously reported Co-based catalysts in Supporting Information Table Figure | (a) NH3 synthesis rate based on Co content over as-synthesized catalysts at 1 and 300 (b) TOF was calculated on the total number of Co atoms basis over the catalysts. (c) N2 and (d) H2 reaction over Co-N2 and Co-NPs catalysts. Download figure Download PowerPoint A test of the Co-N2 catalyst was conducted at 300 °C and 1 MPa. shown in Supporting Information Figure the NH3 synthesis rate a stable of mmol gCo−1 h−1 a The used catalyst was further tested using HR-TEM and EXAFS shown in the Supporting Information Figure no or at different were observed over the used Co-N2 catalyst. Moreover, the Co K-edge EXAFS spectrum of the used Co-N2 catalyst ( Supporting Information Figure showed that existed the Co-N coordination, while no Co-Co coordination was indicating the of a highly stable Co-N2 active in the process of NH3 synthesis. the of these demonstrated the of Co-N2 catalyst in NH3 synthesis at mild conditions. studies studies were conducted to demonstrate the of N2 and H2 activation over the Co-Nx catalysts. The reaction of N2 and H2 usually as related to the and the of hydrogen For most catalysts, the reaction of N2 is to suggesting that the could be the direct dissociation of the N≡N triple bond. shown in Figure the reaction of N2 over Co-N2 was than that of over low reaction of N2 has been reported over Ru-based catalysts supported by or where the of bond than direct N≡N triple bond dissociation was Additionally, the reaction of H2 on Co-NPs was (Figure The demonstrated that the of H2 on Co to hydrogen

Designing highly conductive and (electro)chemically stable inorganic solid electrolytes (SEs) from cost-effective precursors is critical for developing all-solid-state batteries (ASSBs). Herein, we report a series of low-cost zirconium (Zr) -based halide nanocomposite SEs, Li1+2xZr1-xTaxO3xCl5-3x (x = 0.33, 0.4, 0.5), synthesized via mechanochemical interaction between LiTaO3 and ZrCl4. The optimized composition, Li1.8Zr0.6Ta0.4O1.2Cl3.8, exhibits enhanced ionic conductivity from 0.46 to 1.12 mS cm-1 and decreased electronic conductivity. Mechanochemical processing modulates the local structural environments of the halide nanocomposites, facilitating ion transport. Combined characterization, including X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and synchrotron X-ray absorption spectroscopy, reveals that oxygen-substituted nanocomposites with distorted local structures are key to improving ion transport. Finally, we demonstrate ASSBs using Li1.8Zr0.6Ta0.4O1.2Cl3.8 as the SE, single-crystalline LiNi0.8Co0.1Mn0.1O2 (scNCM811) as the cathode, and Li-In alloy as the anode, achieving stable cycling at room temperature and 1 C rate.

Although Li-ion conductivity has been the primary focus during decades of solid-electrolyte research, the mechanical compliance is equally important. For most state-of-the-art solid electrolytes, the mechanical compliance is characterized by the hardness above 1 GPa and Young's modulus above 15 GPa. Here, we report a particularly compliant solid electrolyte, 1.4Li2O-0.75ZrCl4-0.25AlCl3, whose hardness and Young's modulus reach 0.22 and 1.41 GPa, respectively. Meanwhile, it shows an ionic conductivity of 2.55 mS cm-1 at 25 °C and an estimated cost of $43.70 L-1, considerably lower than that of the Li2ZrCl6 solid electrolyte known for cost-effectiveness ($140.01 L-1). The improved mechanical compliance and fast Li-ion transport in 1.4Li2O-0.75ZrCl4-0.25AlCl3 enable decent cell performance. With high positive electrode active material loading above 20 mg cm-2, these two types of cells achieve areal capacities of 3.62 mAh cm-2 (85.78% capacity retention) and 3.92 mAh cm-2 (90.11% capacity retention), respectively, after 100 cycles under 0.1 C at 25 °C. The simultaneous achievement of highly competitive mechanical compliance, Li-ion conductivity, and cost-effectiveness in 1.4Li2O-0.75ZrCl4-0.25AlCl3 have the potential to pave the way for the realization of commercial, practical all-solid-state Li batteries.

All-solid-state sodium (Na) ion batteries (SiBs) are promising high-safety and low cost alternatives to current lithium (Li) ion batteries (LiBs), particularly suitable for the application to large-scale electrical energy storage systems. Development of inorganic solid Na-ion conducting materials used for solid electrolyte is most critical issue to realize all-solid-state SiBs. The solid electrolyte materials should have not only high Na-ion conductivity at room temperature but also chemical and electrochemical stabilities against both cathode and anode active materials. Oxide based solid electrolytes have lower conductivity and poorer deformability than sulfide based one, but they have other advantages such as their chemical stability in air and easiness for handling.Na2M2TeO6 (M = Zn, Mg, Ni, Co, etc.) with a P2-type honeycomb layered structure has been reported as a fast Na-ion conducting oxide [1]. Particularly, Na2Zn2TeO6 (NZTO) is an attractive candidate for a solid electrolyte material because of the high ionic conductivity well above 10-4 S cm-1 at room temperature, wide electrochemical potential window and lower densification temperature than other oxide-based Na-ion conductors such as NASICON and Na-β alumina [2–4]. On the other hand, Na2Ni2TeO6 (NNTO) has been investigated as a cathode active material for SiB operating at 3–4 V vs Na/Na+ [5,6]. Because of the similarity in their crystal structure and constituent elements, NNTO cathode and NZTO as solid electrolyte may be co-sintered without forming undesired secondary phases to fabricate all-solid-state SiBs.In this work, we investigated firstly the reactivity between NNTO and NZTO powders at annealing temperature between 500 ºC and 800 ºC in air. From XRD measurements, it was found that the reaction between NNTO and NZTO is negligible at annealing temperature below 700 ºC while when annealed at 800 ºC, they forms a solid-solution phase without forming any secondary phases. Based on this result, we fabricated NNTO-NZTO laminate via co-sintering NNTO and NZTO pellets at 700 ºC in air. Thicknesses of NNTO and NZTO layers in the laminate were set to 1 mm.From impedance measurements, apparent ionic conductivity of the NNTO-NZTO laminate was estimated to be approximately 0.1 mS cm-1 at 27 ºC, which is close to the prediction with taking into account only the conductivity of individually sintered NNTO (= 0.04 mS cm-1) and NZTO (= 0.36 mS cm-1) at 700 ºC. This indicates that the interfacial resistance between NNTO and NZTO layers is not so large. In addition, using the NNTO-NZTO laminate with NNTO layer thickness of 80 µm, electrochemical Na extraction reaction from NNTO layer through NZTO solid electrolyte was demonstrated via galvanostatic testing at room temperature. Obtained results are very fundamental but can be applied to fabricate all-solid-state SiBs with NNTO cathode and NZTO solid electrolyte via simple co-sintering process in future.

Introduction All-solid-state batteries (ASSBs) utilize non-flammable solid electrolytes, offering enhanced safety. In addition, the application of lithium metal anodes is expected to further improve energy density. Among solid electrolytes, oxide-based solid electrolytes have attracted increasing attention due to their higher stability under atmospheric conditions compared to sulfide-based solid electrolytes. However, oxide-based solid electrolytes exhibit lower ionic conductivity compared to sulfide-based and liquid electrolytes, leading to inferior performance on high-rate cycling.We focused on a novel oxide-based solid electrolyte, lithium lanthanum niobium oxyfluoride (Li1.25La0.58Nb2O6F, LLNOF) [1], which has a bulk ionic conductivity of 7 mS cm-1, which is the highest among oxide-based solid electrolytes reported so far. However, the electrolyte with a high relative density is difficult to be prepared, and the residual voids in the electrolyte easily allow lithium dendrite formation, leading to short circuits. Consequently, improving the sintered density remains an important issue for the LLNOF electrolyte to be used in practical cells. We have reported that the co-addition of alumina (Al2O3) [2] and lithium tungstate (Li2WO4) [3] as sintering aids increased the relative density of lithium lanthanum zirconium tantalate (Li6.4La3Zr1.4Ta0.6O12, LLZT) [4]. In this study, we investigated the effects of various sintering aids on the densification and ionic conductivity of the LLNOF electrolyte. Experimental LLNOF powder used in this experiment was provided by DENSO Corporation [1]. Sintering aids such as Li2WO4, Al2O3, Li2ZrO3, Li2MoO4, and Li2.2C0.8B0.2O3 (LBCO)[5] were used, with each added at 2 wt.%. The LLNOF powder and sintering aids were mixed using a planetary ball mill. A powder of 0.5 g was then pressed into a green pellet at 98 MPa. The green pellet was wrapped in copper foil and sintered at 1000 ℃ for 6 h under Ar atmosphere. The sintered pellet was dry polished to adjust the thickness at 1.0 mm, and Au blocking electrodes were sputtered on both sides of the pellet for conductivity measurements. AC impedance measurements were performed at an applied voltage of 10 mV over the frequency range from 7 MHz to 1 Hz in the temperature range 60 to -20°C. Results and Discussion Table 1 summarizes the relative density, ionic conductivity, and lattice parameters of LLNOF electrolytes with and without sintering aids. The highest relative density (92.7%) was obtained when Li2WO4 was added. However, the bulk ionic conductivity decreased to 2.73 mS cm-1, which was lower than that of LLNOF without sintering aids. The increase in relative density can be attributed to the fact that Li2WO4 has a melting point (742°C) lower than the sintering temperature, leading to the formation of a liquid phase that enhances sintering density.Figure 1 shows the relationship between lattice parameters and ionic conductivity. The ionic conductivity decreased with a decrease in the lattice parameter except for Li2ZrO3. The highest ionic conductivity was observed for the sample prepared without sintering aids. This can be attributed to elemental substitution within LLNOF caused by the addition of sintering aids. Figure 2 shows the cross-sectional SEM images of LLNOF pellets. The pellets prepared with Li2WO4 and LBCO, which generate a liquid phase, exhibit relatively larger grain sizes and fewer voids, resulting in higher relative densities. On the other hand, the sample with Al2O3 has a relatively higher number of residual pores within the grains, which is considered to have led to a decrease in relative density. These results suggest that liquid-phase sintering facilitates the densification of LLNOF.

Lithium-ion batteries are widely developed for vehicle applications and energy storage systems owing to their high power density, long cycle life, and lack of memory effect. The cycling stability of a Li-ion battery plays an important role in its practical application, especially for use in electric vehicles, which is generally affected by the types of electrode materials [1], binder properties [2], and electrolyte compositions [3].Li-ion cells based on LiFePO4cathodes have been considered as one of the most promising candidates for large-scale application due to its low cost, low toxicity, good electrochemical and excellent thermal stability. However, the tendency for capacity degradation behaviour of LFP cells is still seen as a problem for practical application.The capacity fading mechanism of a laminated pouch type 1.0 Ah cell consisting of a graphite anode and an olivine LiFePO4 cathode during a long-term cycling test was studied in this report. The LiFePO4cathodes have a mole ratio of iron to phosphorus in the range of 0.93 to 0.99. As shown in Fig. 1, the LFP cell with a Fe/P ratio of 0.99 has the best cyclic performance at the charge/discharge rate of 2 C/5 C. The cycle life curves of the pouch cell show the number of cycles increases to 2269 cycles with the capacity retention (C.R.) of 80% as the Fe/P ratio increases from 0.93 to 0.99.To investigate the aging mechanism of the LiFePO4 cathode and graphite anode, changes in the crystalline structure through the charge/discharge reactions were analysed by the synchrotron based X-ray diffraction (XRD) experiments. After long-term cycling tests, the appearance of LiOH and LiOH．H2O phases in the cycled anodes reveals that some Li ion released from the LiFePO4 phase during the charge process did not come back to the FePO4 phase, as shown in Fig. 2. Due to fewer lithium ions, some of the cathode material lost electrochemical activity and this brought down the reversible capacity significantly. In addition, the anode with the Fe/P ratio of 0.95 after 506 cycles has relatively stronger peaks than those of the other samples in Fig. 2(b). It indicates that the decrease in the Fe concentration of stoichiometric LiFePO4resulted in a shortage of lithium ion for the cathode material, and consequently the capacity fading rate accelerated.In this study, a combination of X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and electrochemical testing are used to understand the physical and electrochemical characterizations of the graphite anode and the LiFePO4cathode with the different Fe/P mole ratios during long-term cycling tests.

Enhanced lithium dendrite suppression ability through SiO2 substitution in superionic halogen-rich argyrodites and their application in all-solid-state lithium batteries

Development of solid inorganic lithium (Li) ion conducting materials for the use as solid electrolytes is indispensable for the realization of next-generation all-solid-state Li batteries with high safety and reliability. Among various oxide-based solid electrolyte materials, a garnet-type oxide with the formula of Li7La3Zr2O12 (LLZO) has attracted much attention because of its high Li ion conductivity at room temperature, excellent thermal performance, and high stability against Li metal.1,2) However, the formation of a solid-solid interface between LLZO and the Li metal anode is challenging. Poor interfacial connection causes non-uniform Li plating and intergranular penetration of Li dendrite in polycrystalline LLZO when the cell is cycled particularly at high current densities, resulting in internal short-circuit failure.3–5) There is no doubt that the establishment of prevention technology for short-circuit failures is a top priority issue for the development of all-solid-state Li metal batteries.5) On the other hand, from the viewpoint of effective use of material resources, the possibility of reusing LLZO extracted from a solid-state battery after a short-circuit failure occurred is worth considering. In this work, we investigated the reusability of a Ta-doped Li6.55La3Zr1.55Ta0.45O12 (Ta-LLZO) solid electrolyte shorted by Li dendrite growth during electrochemical Li plating/stripping testing for a Li/Ta-LLZO/Li symmetric cell. Ta-LLZO was taken out of a tested cell after the degradation by Li dendrite growth occurred, and then annealed at 700 ºC in air. The annealing temperature was set to suppress possible excess Li loss from Ta-LLZO during post-annealing.6) In the first Li plating/stripping test, the cell was shorted at 0.85 mA cm-2 and the dark gray area with possible Li dendrite growth was confirmed on the surface of Ta-LLZO. This dark gray area turned white but slightly different from the original color of Ta-LLZO by post-annealing. The ionic conductivity of as-synthesized and post-annealed Ta-LLZO was measured and compared. Post-annealed Ta-LLZO retained high room temperature ionic conductivity of 0.82 mS cm-1, which is slightly lower than the conductivity of as-synthesized one (= 0.90 mS cm-1). We also prepared a symmetric cell with the post-annealed Ta-LLZO and Li metal electrodes and the second Li plating/stripping test was carried out. Symmetric cell with post-annealed Ta-LLZO showed stable voltage response. This indicates the possibility of reusing the degraded garnet-type solid electrolyte by Li dendrite growth for an another solid-state Li battery.

Cost effective all‐solid‐state sodium‐ion batteries that operate at room temperature are appealing candidates for use in large‐scale energy storage systems. Although low voltage sulfur was primarily used as cathode for fabrication of all solid-state Na ion battery, limited research was done for cost effective high voltage layered oxide cathode. Here we developed a bulk-type Na-ion all-solid-state battery, fabricated using a high voltage layered oxide cathode Na0.8[Li0.12Ni0.22Mn0.66]O2(NLNMO, 4.2V vs. Na/Na+) and Na3PS4(NPS) glass-ceramic as the solid electrolyte, is expected to have high energy density and improved safety over batteries containing liquid electrolytes. However, the observed interfacial chemical reactions between the oxide cathode and sulfide solid electrolyte as well as electrochemical decomposition of NPS limits the high voltage electrochemical performance. Such reactions were probed using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). To improve the performance, the surface of NLNMO was modified by applying a cost-effective, solution-processed and computationally guided resistive coating of additional oxide layer. STEM revealed that coating layer is amorphous about 5nm thick. After optimizing the coating process, the electrochemical performance of the cell dramatically improved, achieving a specific capacity comparable to that of the liquid cell while exhibiting 80% capacity retention after 300 cycles. This coating method can be an effective strategy for achieving higher electrochemical performance in room temperature all-solid-state Na-ion batteries.

X-ray absorption spectroscopy (XAS) is an element specific spectroscopy sensitive to the local chemical and structural order of the absorber element. XAS is nowadays increasingly used for the speciation analysis of chemical elements owing to the development of new synchrotron radiation facilities worldwide. XAS can be divided into X-ray absorption near edge structure (XANES), which provides information primarily about the geometry and oxidation state, and extended X-ray absorption fine structure (EXAFS), which provides information about metal site ligation. The main advantages of the XAS method are its subatomic (angstrom) resolution, the ability to analyze almost any type of samples including amorphous (non-crystalline) materials, the possibility to analyze such materials in situ requiring minor or no sample preparation. The main limitations of XAS are its sensitivity in themM(or mg g 1) range, the difficulty to deconvolute the bulk data when the sample is composed of a mixture of structures of the absorber element, and the limited chemical selectivity of ligands to within one row of the periodic table. This tutorial will discuss the strengths and limitations of XAS and compare them to those of alternative or complementary methods such as X-ray diffraction and X-ray photoelectron spectroscopy. The tutorial will also present and discuss the specific needs in terms of sample preparation and preservation all along the process of storage and analysis, and discuss the importance of the use of cryogenic methods when XAS is applied to biological samples. Applications in life sciences are reviewed, not exhaustively, with a special emphasis on some characteristic examples. The article ends with some perspectives on future trends of XAS: micro- and nano-XAS, time-resolved XAS, and high energy resolution XAS.

Aqueous Na-ion batteries using Prussian blue materials have inherent advantages in safety, material sustainability, and economic cost. However, it is challenging to obtain long-term cycling stability because many redox reactions have poor intrinsic stability in water. Here, we demonstrate reversible Fe2.4+ to Fe3+ redox reaction of Prussian blue electrodes cycled in a 17 m NaClO4 water-in-salt electrolyte. The cubic phase c-Na1.17Fe[Fe(CN)6]·0.35H2O) derived from monoclinic Prussian blue (m-Na1.88Fe[Fe(CN)6]·0.7H2O) through ball milling delivers excellent cycling stability of >18,000 cycles with >90% capacity retention at the 10C rate. The specific capacity is ∼75 and ∼67 mAh/g at 1C and 10C rates, respectively. Systematic characterizations including electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy have verified the phase transition and iron oxidation state evolution, revealing the mechanism that enables the material's high rate and long durability as the battery cathode.

Halide solid electrolytes (SEs), like Li3InCl6, are promising for high-energy all-solid-state lithium batteries (ASSLBs) due to their high ionic conductivity and compatibility with high-voltage cathodes. Although solvent-mediated synthesis offers a scalable route to phase-pure Li3InCl6, a lack of understanding of critical synthetic parameters, specifically crystallization kinetics, generally yields SE materials with inferior properties. This study systematically investigates the influence of evaporative crystallization temperature and environment on the phase purity, microstructure, defect chemistry of Li3InCl6 SE, and how these factors collectively impact its transport properties and electrochemical performance. It is revealed that slow crystallization under ambient conditions and moderate temperatures (20-60 °C) yields phase-pure Li3InCl6 with the highest ionic conductivity ever reported for the water-mediated route -3.97 mS cm-1 with carbon contact and 2.98 mS cm-1 without. In contrast, high temperature and non-ambient processing introduce structural defects, increase grain-boundary impedance, and promote impurity incorporation, leading to a significant drop in conductivity. Full cells incorporating the optimized Li3InCl6 deliver high capacity even at a low 20 °C, along with excellent stability (>95%) at high areal loading, supported by low and stable cathode interfacial impedance. This work addresses a critical knowledge gap in solvent-mediated synthesis of halide SEs, providing broadly applicable insights for designing phase-pure, high-conductivity materials for next-generation ASSLBs.

Recent years has witnessed extensive interest in nanocrystals due to their unique place bridging single atoms and bulk solids. A special attention has been devoted to spherical metallic nanoparticles, especially those on a suitable support. To understand the mechanisms of catalytic activity of nanoparticles, which was shown to depend strongly on their size and shape [1], a practical and reliable method of nanoparticle characterization is necessary. Recent developments in instrumentation, data analysis and modelling methods led X-ray absorption spectroscopy (XAS) to quickly become the premier technique for catalytic studies. XAS can elucidate the distances of atoms, reveal the average size of particles smaller than ca. 2 nm, provide details on the shape of the nanoparticles, and can be used under in situ or in operando conditions. Its analytical power is demonstrated to match or surpass common laboratory techniques, e.g. chemisorption, X-ray diffraction or transmission electron microscopy, in measuring particle size, shape and inner structure in the nanometre range. Because it is element-specific, XAS can further reveal the mole fractions of atoms in the nanoparticles [2, 3]. While there is no direct relationship between the coordination numbers and interatomic distances to the diameter of spherical nanoparticles, it was shown that the latter can be aproximated to that of a cuboctahedron [4]. For cuboctahedron nanoparticles an exact mathematical equation that correlates the coordination number to the total number of atoms is derived [5]. We have recently shown that the diameter D of the cuboctahedron nanoparticle is related to that of imaginary sphere having the same volume, and can be expressed as a function of the diameter d of the single atom and the number of atoms in the edge of cuboctahedron m, as D ≈ 1.65 m d, and the results were verified by independent experimental techniques [6]. Here we extend this method to estimate the diameter of nanoparticles composed of atoms of different elements forming bimetallic solid solutions, core-shell or aggregate mixtures. Sets of equations for coordination numbers of one component to the other, as well as the interatomic distances between the two elements in these different inner-strucutured mixtures are derived for each system. By testing the experimental data against these predictions, we identify the inner structure of the nanoparticle and apply the appropriate particle size equation. A solid solution of two metals can be recognized as their coordination numbers are in direct relationship to the mole fraction of the components, as well as that the total coordination number of one consitutent equals to that of the other [3]. The diameter of the nanoparticle can be estimated by inserting in the above equation the average atomic diameter d av evaluated by Vegrad’s Law as the weighted mean of the two constituents’ lattice parameters. The relationships for solid solution do not hold for a core/shell system, and the latter can be distinguished by the the similarity of the total coordnation number of the core/shell nanoparticle to that of the monometallic nanoparticle of the same size composed of the core atoms only, so that the diameter of the core/shell nanoparticle can be found by inserting the the atomic diameter of the core atom, d core in the above equation for monometallic shell. Similar conclusion is derived for core/bilayered shell nanoparticles. As the aggregate mixtures are composed of two completely separated nanoparticles with very little interaction between them, the structure can be recognized as the coordination number of one kind of atom to the other is close to zero, and their sizes can be evaluated using the equation for monometallic nanoparticle and the appropriate atomic diameter. It was further shown that the set of equations can be applied to three-component systems using reasonable approximations. Triatomic core/shell particles with a solid solution of two components in the core and a monoatomic shell of the third component, as well as core/inner shell/outer shell nanoparticles in which every layer is composed of different atoms were prepared, and the particle sizes of these systems estimated by our approach are shown to match closely the experimental data obtained by independent techniques.

Controllable tuning of Metal-insulator transition in VxOy thin film has been a field of extensive research. However controlled synthesis of desired Vanadium oxide phase is a challenging task. We have successfully achieved VO2 phase on Silicon substrate after post deposition annealing treatment to the PLD grown as deposited V2O3 thin films. The annealed thin film was characterized by x-ray diffraction (XRD), resistivity, Raman spectroscopy, X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) measurements. XRD confirms the crystalline nature and growth of VO2 phase in thin film. The characteristic MIT was observed from resistivity measurements and transition temperature appeared at lower value around 336 K, compared to bulk VO2. The structural transition accompanied with MIT from lower temperature monoclinic phase to higher temperature Rutile phase became evident from temperature dependent Raman measurements. Chemical state of vanadium was examined using XAS and XPS measurements which confirm the presence of +4 oxidation state of vanadium in thin film.

The all-solid-state lithium battery (ASSB) has received great attention due to its greater safety than the conventional lithium-ion battery (LIB). Sulfide-based inorganic solid electrolytes are an important component to fabricate the ASSB. But to attain a better performance, the ionic conductivity and electrochemical stability of the sulfide-based solid electrolytes need to be improved. In this work, we prepared the metal-oxide-doped/mixed Li7P2S8I0.75Br0.25 lithium superionic conductors by a dry ball-milling process. The high ionic conductivity was achieved by a low-temperature (200 °C) heat-treatment process. The metal-oxide-doped Li7P2S8I0.75Br0.25 solid electrolyte exhibited a higher ionic conductivity value of 7.3 mS cm-1 at room temperature than the bare Li7P2S8I0.75Br0.25 solid electrolyte. The structural characteristics of the prepared solid electrolytes were studied by solid NMR and laser Raman analysis. The electrochemical stability of the prepared solid electrolyte was studied by cyclic voltammetry and DC charge-discharge analysis. The addition of metal oxide increased the electrochemical stability and dry-air stability of the Li7P2S8I0.75Br0.25 solid electrolyte. The Ta2O5-doped Li7P2S8I0.75Br0.25 solid electrolyte was stable even after 300 charge-discharge DC cycles and also 100 h of dry-air exposure. Further, the Ta2O5-doped Li7P2S8I0.75Br0.25 solid electrolyte-based ASSB exhibited a high discharge capacity value of 184 mA h g-1 at 0.1 C rate with 66% initial cycle Coulombic efficiency.