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As one of the most promising power sources in converting and storing chemical energy, aqueous zinc-air batteries (ZABs) stand out because of their high theoretical energy density, low cost, high safety of aqueous electrolyte, and environmental friendliness. Three main types of ZABs including primary ZABs, mechanically rechargeable ZABs, and electrically rechargeable ZABs have been developed up to now.[1] Primary ZABs for single use are usually discarded after the Zn anode is consumed or passivated although other parts of battery remain intact, leading to enormous waste. To address it, the depleted anode and failure electrolyte can be physically replaced to recover the capacity in mechanically rechargeable ZABs. But the cumbersome disassembly/reassembly process and the performance deterioration after every recharge process limit its practical application. In addition, it is not feasible to replace zinc in some integrated systems, such as the large-scale ZAB stack. Electrically rechargeable ZABs with bifunctional oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) catalysts could be returned to the original state by electrochemical charging process, but also face some formidable challenges, such as dendritic zinc deposition, electrode deformation, and hydrogen evolution, limiting the long-term cycling performance. Besides, sluggish kinetics of ORR/OER and Zn passivation result in low energy efficiency, limited depth of discharge and power density. Especially in the resource-constrained and off-grid region, there isn’t external electricity source to charge the electrically rechargeable ZABs which limits their applications. Moreover, the reactions inherently take place on the surface of Zn anode and air cathode, in which the storage and conversion capability of the cell would be essentially constrained by the surface area of electrode and the volume of electrode compartment.The concept of redox targeting (RT) of battery materials offers a feasible solution to address these issues by employing redox mediators (RMs). To tackle the above challenges, here we demonstrate a redox-mediated Zn-air fuel cell (RM-ZAFC) based on the RT reactions of cobalt triisopropanolamine complex (CoTiPA) with O2 and 7,8-dihydroxy-2-phenazinesulfonic acid (DHPS) with Zn metal in the catholyte and anolyte, respectively. Both the 4-electron (4 e-) ORR and Zn oxidation reactions are liberated from the electrode surface and occur inside separate reactor tanks resorting to the RT processes. Upon operation, Co(III)TiPA in the catholyte is electrochemically reduced to Co(II)TiPA on the cathode and chemically oxidized back through ORR in the gas diffusion tank (GDT) into which O2 is fed. In conventional ZABs, ORR takes place on the triple-phase reaction interface of the heterogeneous electrocatalyst, and the catalytic performance is closely related to the density of exposed active site, electrical conductivity and reaction energy barrier. As compared, the redox-mediated ORR in GDT occurs homogeneously in the catholyte in which the dissolved RM could provide a large quantity of rection sites with tunable reaction energy barrier. For the negative side, DHPS-2H is firstly oxidized to DHPS on the anode and circulated into anodic tank, where it is regenerated by oxidizing Zn to ZnO. The discharge product ZnO is formed and deposited on the Zn granules loaded in the tank. After fully discharged, the cell can be feasibly refueled by replacing the Zn granules in the tank instead of disassembling and reassembling the whole cell. In this RM-ZAFC, the energy storage unit is decoupled from the power generation unit, thus offering greater operation flexibility and system scalability with modular design than the conventional ZABs. Compared with the commercial hydrogen tank used in hydrogen fuel cells, Zn granules loaded in the anodic tank present much higher volumetric capacity, greater safety and ease for storage and transportation. Therefore, as an energy conversion and storage device, RM-ZAFC would have great promise for automotive, backup, and stationary power applications.[2] In addition, we also propose an efficient and zinc regeneration method by RT reaction between RM and the product ZnO in RM-ZAFC to avoid the waste of ZnO and reduce the cost.
6High-performance rechargeable zinc-air batteries enabled by cobalt iron anchored on nitrogen-doped carbon matrix as bifunctional electrocatalyst
High-performance rechargeable zinc-air batteries enabled by cobalt iron anchored on nitrogen-doped carbon matrix as bifunctional electrocatalyst
Read more12Copper-cobalt diatomic bifunctional oxygen electrocatalysts based on three-dimensional porous nitrogen-doped carbon frameworks for high-performance zinc-air batteries.
Copper-cobalt diatomic bifunctional oxygen electrocatalysts based on three-dimensional porous nitrogen-doped carbon frameworks for high-performance zinc-air batteries.
Read moreAdvanced Hierarchically 2D and 3D Nanostructured Materials for Electrochemical Clean Energy Conversion
The effective utilization of clean energy and finding alternatives to fossil resources are highly important to ensure the sustainability of human society and are always among the major goals of both chemistry and material science research. Advanced electrochemical devices, such as fuel cells, water electrolysers and metal-air batteries, represent the most promising strategies for clean-energy utilization. In an electrochemical device, the redox reactions are spatially separated by a membrane, allowing direct extraction/transfer of electrons at an electrode-electrolyte interface, which leads to higher intrinsic energy conversion efficiencies, milder process conditions, easy product separation and excellent design features for coupling to renewable energy infrastructure. The performance of such electrochemical processes is fundamentally determined by the physicochemical properties of the electrochemical interfaces, encompassing both the electrocatalyst and the structure of the adjacent electrochemical double layer. Specifically, electrocatalysts play key roles in electrochemical reactions and often limit the performance of entire systems due to their insufficient activity, low durability or high cost. Ideally, the rate, efficiency, and selectivity of the above electrochemical reactions can be substantially improved by developing high-performance electrocatalyst. One of the central tasks for chemists and material scientists is to design and fabricate the high-efficient efficiency but low-cost electrocatalysts systems. The current promising electrochemical reactions mainly focus on the realization of the reversible conversion between chemical and electricity energy, e.g., the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen oxidation reaction (HOR), and hydrogen evolution reaction (HER). Coupling of the above electrochemical reactions provide a solid foundation for various essential electrochemical devices, such as direct hydrogen fuel cells (HOR + ORR); electrolysers (OER + HER); rechargeable zinc (Zn)-air battery (ORR + OER). Therefore, this thesis aims to design and synthesize high-performance electrocatalysts for HER, ORR and OER based on earth-abundant materials with proper hierarchical 2D or 3D nanostructures. Combined with the advanced characterization techniques and density functional theory (DFT) calculations, the relationship between the electrochemical activity and active sites of these earth-abundant electrocatalysts were detailedly explored and confirmed. Furthermore, to emphasize the hierarchical 2D or 3D nanostructures, the actual performance of these electrocatalysts was all evaluated in practical devices including Zn-air battery and proton exchange membrane fuel cell (PEMFC), specifically as follows: (1) The vast majority of the reported HER electrocatalysts performs poorly under alkaline conditions due to the sluggish water dissociation kinetics. In the first work, a hybridization catalyst construction concept is presented to dramatically enhance the alkaline HER activities of catalysts based on 2D transition metal dichalcogenides (TMDs) (MoS2 and WS2). A series of ultrathin 2D-hybrids are synthesized via facile controllable growth of 3d metal (Ni, Co, Fe, Mn) hydroxides on the monolayer 2D-TMD nanosheets. The resultant Ni(OH)2 and Co(OH)2 hybridized ultrathin MoS2 and WS2 nanosheet catalysts exhibit significantly enhanced alkaline HER activity and stability compared to their bare counterparts. The combined theoretical and experimental studies confirm that the formation of the heterostructured boundaries by suitable hybridization of the TMD and 3d metal hydroxides is responsible for the improved alkaline HER activities because of the enhanced water dissociation step and lowers the corresponding kinetic energy barrier by the hybridized 3d metal hydroxides. (2) Nitrogen-coordinated iron atoms on carbon matrix (Fe-N-C) materials are the most active Pt-group-metal-free ORR catalysts but still suffering their low stability and relatively lower activity compared to platinum-based materials. In the second work, Fe and Ni dual sites atomically dispersed in hierarchically ordered macroporous carbon support (Fe-Ni/N-HOMC) was designed and successfully prepared. Isolated atomic Fe- N4 and Ni-N4 active sites were confirmed via various characterizations. The ORR activity and stability of Fe-Ni/N-HOMC in both acid and alkaline electrolyte were much higher than commercial Pt/C and the mono-Fe doping counterpart, which was among the state-of-the-art ORR electrocatalysts. In addition, this 3D ordered interconnected macroporous structure with abundant mesopores and micropores could greatly increase the accessible ORR active site and also enhance the mass transport during the ORR process. When employed as cathodes for PEMFC, we found the excellent ORR activity of Fe-Ni/N-HOMC was completely translated to the cathode in the fuel cell. (3) High-performance bifunctional electrocatalysts with ORR and OER activity is the key to developing efficient rechargeable Zn-air batteries. In the third work, a high-performance bifunctional electrocatalysts for both OER and ORR were synthesized via further hybridizing as-prepared Fe-Ni/N-HOMC with NiFe layer double hydroxides (LDHs). Layered double hydroxides (LDHs) have been reported to be promising OER electrocatalysts with ultrahigh OER performances. The as-synthesized new composites exhibited almost the same ORR activity as Fe-Ni/N-HOMC, revealing that hybridization of NiFe-LDHs would not deteriorate the initial ORR activity. Moreover, the remarkable enhancement of OER activity was observed after the hybridization, which was attributed to the strong coupling of uniformly dispersed small NiFe-LDH nanoparticles with the carbon substrate. The prototype Zn-air battery was assembled using these new composites, which displayed the ultralow voltage gap and long-term stability. (4) Compared with Fe-N-C or Co-N-C based ORR electrocatalysts, the Cu-nitrogen-carbon composites were attracted little attention. However, the natural multicopper oxidases (MCOs) enzymes, such as laccase, can serve as efficient ORR catalyst with almost no overpotential. Inspired by their tris-copper centers in MCO, one novel Cu-nitrogen-carbon composite (Cu SAs/N-CS) with atomic Cu coordination sites were synthesized via the pyrolysis of the Cu-involved metal-organic-framework. The copper contents in Cu SAs/N-CS reaches as high as 3.17 wt.%, and the average distances of adjacent copper sites was around only 3.1 Å. Due to the synergetic effect of abundant single atomic copper active sites with closer distance and ultrathin carbon nanosheet structure, Cu SAs/N-CS exhibited superior ORR activity exceeding commercial Pt/C catalyst, methanol tolerance, and long-term stability in both alkaline and neutral electrolyte. In summary, four kinds of new composites were successfully designed and prepared as high-performance electrocatalysts for HER, ORR and OER. Multi-dimensional heterostructures, atomic metal coordination sites and 3D hierarchically porous structure were designed and observed, which contributed greatly to improve activities of these composites. This thesis suggests several new viewpoints in the design of electrocatalysts based on earth-abundant materials: (i) offering new strategies for the preparation of novel 2D and 3D heterostructures as electrocatalysts; (ii) expanding methods for the synthesis of atomic metal coordination sites and evaluating their activities for ORR; (iii) evaluating the practical performances of achieved electrocatalysts in proton exchange membrane fuel cell and Zn-air battery; (iv) attempting to explain reaction mechanisms of some electrocatalysts by DFT calculation.
Read moreHighly efficient nitrogen-doped three-dimensional interconnected porous carbon supported heterogeneous Co/MnO nanoparticles oxygen electrocatalysts for rechargeable zinc air batteries
Highly efficient nitrogen-doped three-dimensional interconnected porous carbon supported heterogeneous Co/MnO nanoparticles oxygen electrocatalysts for rechargeable zinc air batteries
Read more191Defect-rich carbon fiber electrocatalysts with porous graphene skin for flexible solid-state zinc–air batteries
Defect-rich carbon fiber electrocatalysts with porous graphene skin for flexible solid-state zinc–air batteries
1Synergistic Fe–Ni dual-atom sites on hollow carbon enabling high-performance rechargeable zinc–air batteries
The advancement of rechargeable zinc–air batteries (ZABs) hinges critically on the development of efficient and durable bifunctional oxygen electrocatalysts. Herein, we report an atomically dispersed Fe–Ni bifunctional catalyst loaded on a hollow carbon framework (FeNi-hCN) through a density difference-assisted strategy. This unique architecture, leveraging the synergistic interplay between Fe and Ni atoms and the advantageous properties of the hollow carbon support, endows the catalyst with exceptional bifunctional oxygen electrocatalytic activity: a half-wave potential (E1/2) of 0.91 V for the oxygen reduction reaction (ORR) and overpotential of only 330 mV at 10 mA cm−2 for the oxygen evolution reaction (OER). Remarkably, the catalyst demonstrates outstanding stability, retaining its activity after 100 000 accelerated degradation test (ADT) cycles and 240 hours of continuous OER operation. When deployed as the air cathode in aqueous ZABs, this catalyst achieves a high peak power density of 212 mW cm−2 and stable cycling for 560 hours, outperforming a Pt/C + RuO2 combination. Density functional theory (DFT) calculations elucidate that the Fe–Ni dual sites synergistically lower the adsorption energy of the critical *OOH intermediate, thereby reducing the overall energy barriers for both ORR and OER pathways. This density difference-assisted method also works for other MOFs like UiO-66 and HKUST-1, enabling diverse high-performance carbon-supported catalysts.
Read more2Electrodeposited Zn-Mn on three-dimensional electrodes as anodes in liquid and quasi-solid-state zinc-air batteries
Electrodeposited Zn-Mn on three-dimensional electrodes as anodes in liquid and quasi-solid-state zinc-air batteries
37Highly exposed Fe-N4 active sites in porous poly-iron-phthalocyanine based oxygen reduction electrocatalyst with ultrahigh performance for air cathode.
Progress in the development of efficient electrocatalysts for oxygen reduction reactions is imperative for various energy systems such as metal-air batteries and fuel cells. In this paper, an innovative porous two-dimensional (2D) poly-iron-phthalocyanine (PFe-Pc) based oxygen reduction electrocatalyst created with a simple solid-state chemical reaction without pyrolysis is reported. In this strategy, silicon dioxide nanoparticles play a pivotal role in preserving the Fe-N4 structure during the polymerization process and thereby assist in the development of a porous structure. The new polymerized phthalocyanine electrocatalyst with tuned porous structure, improved specific surface area and more exposed catalytic active sites via the 2D structure shows an excellent performance towards an oxygen reduction reaction in alkaline media. The onset potential (E = 1.033 V) and limiting current density (I = 5.58 mA cm-2) are much better than those obtained with the commercial 20% platinum/carbon electrocatalyst (1.046 V and 4.89 mA cm-2) and also show better stability and tolerance to methanol crossover. For practical applications, a zinc-air (Zn-air) battery and methanol fuel cell equipped with the PFe-Pc electrocatalyst as an air cathode reveal a high open circuit voltage and maximum power output (1.0 V and 23.6 mW cm-2 for a methanol fuel cell, and 1.6 V and 192 mW cm-2 for the liquid Zn-air battery). In addition, using the PFe-Pc electrocatalyst as an air cathode in a flexible cable-type Zn-air battery exhibits excellent performance with an open-circuit voltage of 1.409 V. This novel porous 2D PFe-Pc has been designed logically using a new, simple strategy with ultrahigh electrochemical performances in Zn-air batteries and methanol fuel cell applications.
Read moreIn Situ Growth of Nife Alloy Nanoparticles Embedded into N-Doped Bamboo-like Carbon Nanotube As a Bifunctional Electrocatalyst for Zn-Air Battery
Developing low-cost catalysts for electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with superior performance in alkaline solution is of significance for large-scale application in aqueous zinc-air batteries (ZABs). Herein, we describe in situ design of embedded NiFe nanoparticles into the N-doped bamboo-like carbon nanotube (NBCNT) with high catalytic performance and stability. The obtained NiFe@NBCNT hybrid exhibits a high electrochemical activity and stability with an unexpectedly low overpotential of ~195 mV for OER at 10 mA cm-2, and an onset potential at 1.03 V for ORR, superior to the state-of-the-art Pt/C and RuO2 catalysts. Additionally, compared to the mixture Pt/C and RuO2 cathode, the ZAB based on the NiFe@NBCNT cathode displays lower overpotential (0.80 V), higher stable round-trip efficiency (58.3%) and improved power density for 200 cycles at 10 mA cm-2. Apparently, the obtained results indicate that NiFe@NBCNT hybird is proven to be one of the best non-noble metal catalysts for achieving commercial implementation of rechargeable ZABs.
Read more11Spinel Type Mn−Co Oxide Coated Carbon Fibers as Efficient Bifunctional Electrocatalysts for Zinc‐Air Batteries
Mn−Co mixed oxide nanoparticles were coated onto carbon fibers (CFs) derived from asphaltene through a facile coating process. Homemade gas diffusion layers (GDLs) were prepared with the coated CFs to be employed as air electrodes and bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts for Zn‐air batteries (ZAB). The Mn−Co oxide was identified as a cubic spinel phase (MnCo2O4) by transmission electron microscopy (TEM) and X‐ray photoelectron spectroscopy (XPS). The composite air electrode showed excellent catalytic activity towards ORR/OER, outperforming the benchmark Pt‐RuO2 catalyst in both half‐cell and full‐cell configurations with discharge/charge efficiencies of 63.7 % and 60.0 % at 10 and 20 mA cm−2, respectively. After 200 cycles (100 h) at 10 mA cm−2 the final efficiency of the composite electrode (58.9 %) was still superior to that of Pt−Ru (43.2 %).
Read more72Rechargeable sunlight-promoted Zn-air battery constructed by bifunctional oxygen photoelectrodes: Energy-band switching between ZnO/Cu2O and ZnO/CuO in charge-discharge cycles
Rechargeable sunlight-promoted Zn-air battery constructed by bifunctional oxygen photoelectrodes: Energy-band switching between ZnO/Cu2O and ZnO/CuO in charge-discharge cycles
Read more(Digital Presentation) ORR/OER Activity and Rechargeable Zinc-Air Battery Performance of B Site Doped Double Perovskite NdBaCoXO5+δ (X= Fe, Ni, Mn)
Renewable energy systems and designing economically viable electrochemical energy storage systems is essential to decrease environmental pollution concerns while meeting the growing energy demand. Among the various energy storage devices, rechargeable zinc-air batteries (RZAB) have attracted great attention due to their relatively high specific energy (1218 W.h/kg), and volumetric energy density (6136 W.h/L) cost-effectiveness, and environmental friendliness, comparable to that of lithium–air batteries [1]. However, the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during the discharge and recharge process of the air cathode on RZAB prevents large-scale application. So far noble metals (Pt, Ru, Ir) and their alloys (Pt-Ru/C) are used as bifuctional oxygen electrocatalysts in commercial rechargeable RZAB, yet they are too expensive to be viable for large-scale commercial applications. Therefore, designing robust and cost-effective bifunctional oxygen electrocatalysts is prime of importance for RZAB to be commercialized [2]. One of the most promising oxygen bifunctional catalyst are perovskite oxides due to their structural and compositional flexibility [3]. Moreover, the electronic structure of perovskite oxides can be tuned by varying the transition metals at the B site and thus their electrocatalytic performance [4-5].In this work, first we will demonstrate phase pure fabrication of double perovskite oxide series of NdBaCoXO5+δ (X= Fe, Ni, Mn). Second, OER and ORR performances of the series of NdBaCoXO5+δ (X= Fe, Ni, Mn) will be explained in relation with their electronic structure and work function. Here, we applied NdBaCoMnO6 on a home-made RZAB as air cathode, according to its bifunctional index. Therefore, we will finally present charge-discharge performance of RZAB with NdBaCoMnO6 as air cathode. J. Fu, Z. P. Cano, M.G. Park, A. Yu, M. Fowler, Z. Chen, Advanced Materials, 29, 1604685 (2016).Y. Tong, J. Wu, P. Chen, H. Liu, W. Chu, C. Wu, Y. Xie, Journal of the American Chemical Society, 140, 11165-11169 (2018).W. Yin, B. Weng, J. Ge, Q. Sun, Z. Li, Y. Yan, Energy & Environmental Science, 12, 442-462 (2019).J. Ahmed, N. Alhokbany, M. Ubaidullah, S. Mutehri, M. M. Khan, S. M. Alshehri, Ceramics International, 46, 20038-20044 (2020).A. Mulder, N. Benedek, J. Rondinelli and C. Fennie, Advanced Functional Materials, n/a-n/a (2013).
Read morePhotoactive Electrocatalyst with Staggered p-n Heterojunction for Rechargeable Zn-Air Batteries
Rechargeable zinc-air batteries (RZBs) demonstrate significant potential as next-generation batteries as they are non-flammable, resource-abundant, cost-efficient, feasible for ambient air operation, and have remarkable theoretical energy density (1086 Wh kg-1). However, the development of RZBs needs to address many challenges to speed up their commercialization. For example, low round-trip efficiency during cycling is caused by retarded reactivity of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the air cathode. An air cathode with deficient electrocatalytic kinetics creates a large voltage gap, especially when the practical charge voltage is > 2.0 V, during the charging and discharging process. Moreover, the cycle life of the RZBs is limited owing to the structural degradation of air cathodes working under high charge voltage. Therefore, it is essential to improve both the round-trip efficiency and structural durability of air cathodes to ensure further development and commercialization of RZBs. For efficient energy generation and storage, photo-enhanced RZBs that combine photochemical and electrochemical energy conversion and storage with the help of solar energy, are a promising research focus. Photo-enhanced RZBs require a photoactive OER/ORR bifunctional cathode that is not merely an electrochemical catalyst but also a photo-active catalyst.In the present study, we developed a photoactive bifunctional air-electrocatalyst with a staggered p-n heterojunction band gap structure, comprising n-type g-C3N4 and p-type copper-doped ZIF-67 (CuZIF-67) composite, to accelerate sluggish OER/ORR processes via a durable structure and stable long-cycle-life performance for photo-enhanced RZBs. g-C3N4/CuZIF-67 has a suitable band gap, which ensures wide-range light absorption in the UV–Vis–NIR region, and stimulates more electrons to participate in ORR/OER electrocatalytic activity. Besides, it has a staggered bandgap structure and a BEF at the p-n junction of the catalyst, which improves electron–hole pairs separation efficiency, lowers overpotential, promotes ORR/OER electrocatalytic activity, and eventually enhances the efficiency of RZBs (the voltage gap was significantly decreased by 14% with simulated solar light irradiation). Moreover, a high concentration of pyrrolic-N groups in the cathode material, resulting in the excellent electrochemical durability of RZBs during charge/discharge cycles. The photo-enhanced RZB based on the g-C3N4/CuZIF-67 bifunctional catalyst exhibits good round-trip efficiency of 60% (2 mA cm-2) with a significantly decreased voltage gap (from 0.92 to 0.81 V) after 1000 cycles, under simulated solar light irradiation. It can be concluded that staggered p-n heterojunction and pyrrolic nitrogen-rich groups play an important role in efficient and durable photo-enhanced Zn-air batteries.
Read more234In-situ enriching active sites on co-doped Fe-Co4N@N-C nanosheet array as air cathode for flexible rechargeable Zn-air batteries
In-situ enriching active sites on co-doped Fe-Co4N@N-C nanosheet array as air cathode for flexible rechargeable Zn-air batteries
Read more24Activated palladium deposited on defect-rich carbon and cobalt oxide composite materials as bi-functional catalysts for stable rechargeable Zn–air battery
Activated palladium deposited on defect-rich carbon and cobalt oxide composite materials as bi-functional catalysts for stable rechargeable Zn–air battery
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