Multi-scale porous nickel iron oxyhydroxide-based electrodes for highly efficient oxygen evolution reaction

Green hydrogen production from renewable energy can help overcome difficult energy challenges worldwide. It can help decarbonize hard-to-abate sectors such as steel, chemicals, and ammonia fertilizer. Polymer Electrolyte Membrane (PEM) water electrolyzer serves as a promising technology when coupled with the fluctuating renewable energies for hydrogen production, with the advantages of fast response, dynamic operation, and excellent overload capacity. However, the only technically feasible anode catalysts for PEM are built on scarce iridium and require more than 40 years of annual production for 1 TW-scale. The scarce metal iridium has become a bottleneck limiting the scale development of PEM water electrolysis technology. Therefore, identifying earth-abundant catalysts with high activity and acid tolerance is essential to realizing large-scale hydrogen production via water electrolysis. Various 3d transition metals have been investigated as potential OER catalysts. In 2019, we reported how manganese oxide shows exceptional stability among earth-abundant materials for oxygen evolution reaction (OER) in acid. At the time, non-precious metal catalysts had difficulty maintaining activity for more than a week at 10 mA cm-2. In comparison, manganese oxide (γ-MnO2) was able to electrolyze water for over 11 months at 10 mA cm-2. This was made possible by identifying a stable potential window for γ-MnO2 in which the OER can be catalyzed efficiently while simultaneously suppressing deactivation pathways. After that, a binary spinel oxide catalyst (Co2MnO4) was synthesized by mixing stable manganese with active cobalt using a thermal decomposition method. Cobalt oxides were shown to be active for the OER but unstable in acid. By incorporating Mn into the Co3O4 spinel lattice, the lifetime was extended by two orders of magnitude while maintaining the activity. The water electrolysis with Co2MnO4 in acid can be sustained over 1500 hours at 200 mA cm-2. The activation barrier of the obtained spinel Co2MnO4 is comparable to state-of-the-art iridium oxides, which are reported to have activation energies of 25-30 kJ mol-1 in acidic conditions. The catalyst dissolution was experimentally analyzed by spectroscopy methods. It is clarified that the tetrahedral Co is the preferable dissolution site and the dissolution rate is suppressed in Co2MnO4 compared to Co3O4, resulting in outstanding stability. The active working time of Co2MnO4 as a function of current density for the OER reaction and other earth-abundant electrocatalysts reported in the literature were summarized. The marked improvement of the activity and stability in acid makes cobalt manganese spinel materials an intriguing candidate for non-noble metal water electrolysis. Acknowledgments: This work was supported by the New Energy and Industrial Technology Development Organization (NEDO). Figure caption: Long-term stability of Co2MnO4 during the OER in acid. a, Time dependence of the electrochemical potential necessary to perform OER at 100, 200, 500 and 1,000 mA cm-2 geo in H2SO4 (pH 1) and H3PO4 (pH 1), respectively. The stabilities of Co3O4 and γ-MnO2 in H2SO4 (pH 1) are shown for comparison. All the experiments were performed at 25 °C using an FTO substrate except for curve IX, for which a Pt/Ti mesh was used. b, A comparison of the stability of Co2MnO4 with Co3O4 and other Earth-abundant OER catalysts reported in the literature12-28 (Please refer Nat Catal 5, 109–118 (2022)) (upwards and downwards triangles represent lifetime and operation time, respectively). The measurements were performed under acidic conditions. Data points with roman numerals (I to XI) correspond to curves I to XI in a. Diagonal lines indicate the total amount of charge transferred before deactivation. Only studies that report stability at pH < 3 were included in the literature survey. Figure 1

Electrochemical water splitting is an important process to produce hydrogen and oxygen for energy storage and conversion devices. However, it is often restricted by the oxygen evolution reaction (OER) due to its sluggish kinetics. To overcome the problem, precious metal oxide-based electrocatalysts, such as RuO2 and IrO2, are widely used. The lack of availability and the high cost of precious metals compel researchers to find other resources for the development of cost-effective, environmentally friendly, earth-abundant, nonprecious electrocatalysts for OER. Such catalysts should have high OER performance and good stability in comparison to those of available commercial precious metal-based electrocatalysts. Herein, we report an inexpensive fabrication of bimetallic iron-nickel nanoparticles on FeNi-foil (FeNi4.34@FeNi-foil) as an integrated OER electrode using a one-step calcination process. FeNi4.34@FeNi-foil obtained at 900 °C shows superior OER activity in alkaline solution with an overpotential as low as 283 mV to achieve a current density of 10 mA cm-2 and a small Tafel slope of 53 mV dec-1. The high performance and durability of the as-prepared nonprecious metal electrode even exceeds those of the available commercial RuO2 and IrO2 catalysts, showing great potential in replacing the expensive noble metal-based electrocatalysts for OER.

The development of efficient and low-cost oxygen evolution reaction (OER) catalysts is essential for the generation of clean hydrogen energy from water splitting. Herein, a novel hierarchical urchin-like cobalt-copper (hydr)oxide in situ grown on copper foam (CoCuOx Hy (S)/CF) was synthesized through the electrochemical transformation of cobalt-copper sulfides (Co9 S8 -Cu1.81 S) via anodization process. This CoCuOx Hy (S)/CF anode exhibited a low overpotential (η) of 274 mV at a current density of 100 mA cm-2 with a robust durability over a period of 40 h when operated at 10 mA cm-2 . Further investigations imply that the unique nanowires aggregated urchin-like structure of CoCuOx Hy (S) derived from the in situ anion exchange process could facilitate the exposure of active sites and accelerate electron transfer. More importantly, the incorporation of copper resulted in an electronic delocalization around the cobalt species, which contributed to reach a high-valent catalytically active cobalt species and further improved the OER performance.

Tungsten oxide decorating-regulated iron-nickel oxide heterostructure as electrocatalyst for oxygen evolution reaction

Rational design of transition-metal phosphide (TMPs)-based electrocatalysts can effectively promote oxygen evolution reaction (OER). Herein, the novel efficient Ni2P/Fe3O4 porous nanosheets arrays supported on Ni foam (Ni2P/Fe3O4/NF) as alkaline OER catalysts were synthesized using structural and interfacial engineering. The three-dimensional (3D) porous hierarchical structure of Ni2P/Fe3O4/NF provides abundant active sites for OER and facilitates the electrolyte diffusion of ions and O2 liberation. Furthermore, the strong interfacial coupling and synergistic effect between Ni2P and Fe3O4 modify the electronic structure, resulting in the enhanced intrinsic activity. Consequently, the optimized Ni2P/Fe3O4/NF exhibits excellent OER performance with low overpotentials of 213 and 240 mV at 60 and 100 mA cm-2 in 1.0 M KOH, respectively, better than the RuO2/NF and most Ni/Fe-based OER catalysts. Impressively, it can maintain its catalytic activity for at least 20 h at 60 mA cm-2. In addition, the relationship between the structure and performance is fully elucidated by the experimental characterizations, indicating that the metal oxyhydroxides in situ generated on the surface of catalysts are responsible for the high OER activity.

Growing demand for sustainable, clean, efficient energy conversion system has derived tremendous interest to develop cost-effective and highly efficient electrocatalysts for oxygen evolution reaction (OER). Sulfides have recently attracted great attention due to their highly efficient electrocatalytic activity. MoS2 has been verified as an efficient catalyst toward OER because of its durability, cost-efficiency and high activity. However, binder and extra conductive materials are required to attach electrocatalyst on a conductive substrate which will result in restricted active surface areas, undesirable interfaces and lots of dead volumes. Binder-free self-supported material can eliminate these problems. Herein, we synthesize self-supported binder-free MoS2 on 3D porous nickel foam (NF) with excellent activity and stability via a facile hydrothermal method. The MoS2@NF electrode is tested in 0.1mol KOH by linear sweep voltammetry (LSV), electrochemical surface area (ECSA) and electrochemical impedance spectroscopy (EIS). Compared with different substrates (Cu foam, NF, Cu paper and carbon paper), MoS2@NF electrode where NF as substrate shows the lowest overpotential at 10mA cm-2 of 359mV for OER. Furthermore, the overpotential at 10mA cm-2 after 10hr is 419mV, which demonstrates high stability and activity. Such high electrochemical performance may attribute to the following reasons: 1) the large ECSA and good conductivity, that improves utilization of electroactive sites and electron transfer; 2) the unique 3D porous structure, that facilitates electrolyte penetration and reactant/product diffusion; and 3) the sulfur vacancy in MoS2, that accelerates the O-H bond breaking.

Evaluation of unique catalysts of the iron group metals with activity in the OER region similar to that of scarce metals is of great importance to achieve sustainable production of H2 on a large scale. Herein, we report the unique nanosheets of nickel iron hydroxy carbonate hydrate (NiFeHCH) which were prepared through a wet-chemical route within 1 h of reaction time, acting as an efficient electrocatalyst for the oxygen evolution reaction (OER) in both alkaline and near-neutral media. The NiFeHCH was prepared with different concentrations of Fe in different ratios: 1:0.2, 1:0.4, 1:0.6, 1:0.8, and 1:1. Among them, nanosheets of NiFeHCH (1:0.2)were found to have superior OER activity, which required an overpotential of 250 mV to reach 20 mA cm-2 with a very low Tafel slope value of 39 mV/decade in 1 M KOH. Nanosheets with other ratios also had comparable OER activity with overpotentials ranging from 256 to 290 mV with Tafel slope values from 39 to 49 mV/decade. Nanosheets of NiFeHCH electrocatalysts screened for the OER in 1 M NaHCO3 (pH ∼8.5) required overpotentials for all of the ratios ranging from 389 to 507 mV at 10 mA cm-2 and Tafel slope values from 155 to 205 mV/decade, of which nanosheets of NiFeHCH (1:0.4) showed better activity by requiring an overpotential of 389 mV at 10 mA cm-2 and Tafel slope value of 155 mV/decade. With these fruitful advantages, these prepared nanosheets of NiFeHCH can be a better alternative to scarce metals for industrial water electrolysis.

Water electrolysis is considered as a key energy source to produce hydrogen for achieving a clean and sustainable society. Improving the sluggish kinetics of the oxygen evolution reaction (OER) is focused to overcome the limit efficiency of water electrolysis. Transition metals, especially Ni, are one of the most promising materials for the alkaline OER because of good catalytic activities, stabilities and cost efficiency. Ni based materials, such as Ni oxyhydroxides, hydroxides, phosphides and sulfides, are intensively developed for use as OER catalysts. Recently, the sulfurization of transition metals is introduced as an effective method to improve the intrinsic electrocatalytic activities. The role of S has been summarized in 2 ways. S accelerates the regeneration of transition metals in alkaline media that S is dissolved and exchanged with O species. Mullins et al. reported Nickel oxide derived from Ni-S. It exhibits amorphous and large active surface morphology which is favorable OER. The other role is that remaining S modulates the electronic structures of Ni catalysts reducing the energy barrier for the OER. Wu et al. developed ultrathin Fe-doped Ni3S2 for overall water splitting. Based on density functional theory calculations, the Fe-doped Ni3S2 surface exhibits an optimized energy for water adsorption and dissociation, which enhances the intrinsic activity for the OER. However, in-situ/operando experimental studies regarding the effects of residual S are rare.Herein, we report the role of the remaining S in Ni catalysts that exhibit longer Ni-O bonding in the NiOOH phase produced in-situ. C-supported Fe- and Co-doped nickel sulfide catalysts (NiFeCo-S/C) is prepared using a simple impregnation method with heating under an H2S atmosphere. We tested the electrochemical properties of the NiFeCo-S/C in alkaline media of 1 M KOH. It achieved current density of 10 mA cm-2 with only overpotential of 267.2 mV. Also, it maintained the OER activities for 24 h at current densities of 10 and 50 mA cm-2, respectively. Moreover, the prepared catalyst was analyzed the change of electronic structure and bonding group using in-situ/operando X-ray absorption spectroscopy (XAFS) and surface-enhanced Raman spectroscopy (SERS) under OER condition. Based on these results, we could elucidate the effects of the remaining S during the OER. Figure 1

Designing highly active and robust electrocatalysts for oxygen evolution reaction (OER) is crucial for many renewable energy storage and conversion devices. Here, self-supported monolithic hybrid electrodes that are composed of bimetallic cobalt-molybdenum nitride nanosheets vertically aligned on 3D and bicontinuous nanoporous gold (NP Au/CoMoNx ) are reported as highly efficient electrocatalysts to boost the sluggish reaction kinetics of water oxidation in alkaline media. By virtue of the constituent CoMoNx nanosheets having large accessible CoMoOx surface with remarkably enhanced electrocatalytic activity and the nanoporous Au skeleton facilitating electron transfer and mass transport, the NP Au/CoMoNx electrode exhibits superior OER electrocatalysis in 1 m KOH, with low onset overpotential (166 mV) and Tafel slope (46 mV dec-1 ). It only takes a low overpotential of 370 mV to reach ultrahigh current density of 1156 mA cm-2 , ≈140-fold higher than free CoMoNx nanosheets. The electrocatalytic performance makes it an attractive candidate as the OER catalyst in the water electrolysis.

Perovskites (ABO3) with transition metals in active Bsites are considered alternative catalysts for the water oxidation tooxygen through the oxygen evolution reaction (OER) and for theoxygenreduction through the oxygen reduction reaction (ORR) back to water. We have synthesized a double perovskite (A2BB'O6) with different cations in A, B, and B' sites, namely, (La1.5Sr0.5)A(Ni0.5Mn0.5)B(Ni0.5Ru0.5)B'O6 (LSNMR), which displays an outstanding OER/ORR bifunctional performance. The composition and structure of the oxide has been determined by powder X-ray diffraction, powder neutron diffraction, and transmission electron microscopy to be monoclinic with the space group P21/ n and with cationic ordering between the ions in the B and B' sites. X-ray absorption near-edge spectroscopy suggests that LSNMR presents a configuration of ∼Ni2+, ∼Mn4+, and ∼Ru5+. This bifunctional catalyst is endowed with high ORR and OER activities in alkaline media, with a remarkable bifunctional index value of ∼0.83 V (the difference between the potentials measured at -1 mA cm-2 for the ORR and +10 mA cm-2 for the OER). The ORR onset potential ( Eonset) of 0.94 V is among the best reported to date in alkaline media for ORR-active perovskites. The ORR mass activity of LSNMR is 1.1 A g-1 at 0.9 V and 7.3 A g-1 at 0.8 V. Furthermore, LSNMR is stable in a wide potential window down to 0.05 V. The OER potential to achieve a current density of 10 mA cm-2 is 1.66 V. Density functional theory calculations demonstrate that the high ORR/OER activity of LSNMR is related to the presence of active Mn sites for the ORR- and Ru-active sites for the OER by virtue of the high symmetry of the respective reaction steps on those sites. In addition, the material is stable to ORR cycling and also considerably stable to OER cycling.

Oxygen evolution reaction (OER) represents a highly important electrochemical transformation in energy storage and conversion technologies. Considering the low rate of this four-electron half-reaction, there is a demand for efficient, stable, and noble-metal-free electrocatalysts to improve the kinetic and economical parameters. In this work, a new pillared-MOF@NiV-LDH nanocomposite based on a CoII metal-organic framework (pillared-MOF) and heterometallic Ni/V-layered double hydroxide (NiV-LDH) was assembled via a simple protocol, characterized, and explored as an electrocatalyst in OER. A remarkable electrocatalytic efficiency of pillared-MOF@NiV-LDH in 1 M KOH is evidenced by a low overpotential (238 mV at 10 mA cm-2 current density) and a small value of the Tafel slope (62 mV dec-1). These parameters are very close to those of the reference IrO2 electrocatalyst and are superior to the majority of the LDH- and MOF-based systems previously applied for OER. Excellent stability of pillared-MOF@NiV-LDH was confirmed by the chronopotentiometry tests for 70 h and linear-sweep voltammetry after 7000 cycles. Features such as rich electroactive sites, porous structure, high surface area, and synergic effect between pillared-MOF and NiV-LDH are likely responsible for the remarkable electrocatalytic efficiency of this electrocatalyst in OER. Despite prior reports on the application of NiV-LDH in OER, the present study describes the first example where this type of LDH is blended with MOF to generate a nanocomposite material. The interface between the two components of the composite can improve the electronic structure and, in turn, the electrocatalytic behavior. The introduction of this composite paves the way toward the synthesis of other multicomponent materials with potential applications in different energy fields.

The oxygen evolution reaction (OER) at the anode is of prime importance in electrochemical water splitting. Recently, layered double hydroxide (LDH) has been considered as one of the most effective materials for OER catalysts which are prone to hydrolysis and oxidation under OER conditions. Metal-organic frameworks (MOFs) are new class of porous materials with high crystallinity and high internal surface area. Based on their properties, the design of LDH based on morphology-controlled MOFs is gaining increasing attention. In this study, we report a novel approach to fabricate hollow leaf-shaped iron doped nickel cobalt LDH (Fe-NiCoLDH) based on 2D leaf-shaped ZIF (ZIF-L). Iron doping played an important role to enhance the specific surface area as well as the pore structure, resulting in improvement of the OER performance. Among the investigated Fe concentrations (from 40 to 80 mg) in this study, Fe60-NiCo LDH showed the highest electrocatalyst performance for OER of 10 mA cm-2 at 253 mV as well as high stability for 20 h. The design of nanostructures such as leaf-shaped LDH has great potential in enhancing OER efficiency.

Thin-film iron-oxide nanobeads as bifunctional electrocatalyst for high activity overall water splitting

The sluggish reaction kinetics of oxygen evolution reaction (OER) significantly limit the efficiency of electrochemical water splitting (EWS) process, making the development of efficient and stable OER electrocatalysts for sustainable EWS important but still challenging to achieve. Herein, a light-assisted improved design of low-budget carbonized wood (CW) with outstanding OER performance is developed by firmly growing CoFe2O4 nanorods and Ag nanoparticles on the CW channels to form self-supporting electrode (CoFe2O4/Ag-CW). The coordination of active CoFe2O4/Ag and porous CW framework results in substantial effective interfaces and abundant electrochemical active sites, and accelerated electrolyte diffusion, electron transfer, and oxygen escaping. Electrochemical measurements and density functional theory calculations suggest the presence of dual microparticle synergies, conducive to optimizing the electronic structure of CoFe2O4/Ag-CW and lowering the energy barrier of O-H bond breaking in H2O for remarkably enhanced OER activity. Under light field assistance, CoFe2O4/Ag-CW exhibits excellent photothermal effect and carrier separation efficiency with ultralow overpotential of 258 mV and long-term stability at 100 mA cm-2. The photothermal effect and the generation of photogenerated carriers enhance OER dynamics and charge transfer efficiency, leading to improved OER performance under light exposure. Overall, the proposed strategy looks promising for efficient and low-cost oxygen generation.

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.