The electrochemical reduction of oxygen to water and the evolution of oxygen from water are two important electrode reactions extensively studied for the development of electrochemical energy conversion and storage technologies based on oxygen electrocatalysis. The development of an inexpensive, highly active, and durable nonprecious-metal-based oxygen electrocatalyst is indispensable for emerging energy technologies, including anion exchange membrane fuel cells, metal-air batteries (MABs), water electrolyzers, etc. The activity of an oxygen electrocatalyst largely decides the overall energy storage performance of these devices. Although the catalytic activities of Pt and Ru/Ir-based catalysts toward an oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER) are known, the high cost and lack of durability limit their extensive use for practical applications. This review article highlights the oxygen electrocatalytic activity of the emerging non-Pt and non-Ru/Ir oxygen electrocatalysts including transition-metal-based random alloys, intermetallics, metal-coordinated nitrogen-doped carbon (M-N-C), and transition metal phosphides, nitrides, etc., for the development of an air-breathing electrode for aqueous primary and secondary zinc-air batteries (ZABs). Rational surface and chemical engineering of these electrocatalysts is required to achieve the desired oxygen electrocatalytic activity. The surface engineering increases the number of active sites, whereas the chemical engineering enhances the intrinsic activity of the catalyst. The encapsulation or integration of the active catalyst with undoped or heteroatom-doped carbon nanostructures affords an enhanced durability to the active catalyst. In many cases, the synergistic effect between the heteroatom-doped carbon matrix and the active catalyst plays an important role in controlling the catalytic activity. The ORR activity of these catalysts is evaluated in terms of onset potential, number of electrons transferred, limiting current density, and durability. The bifunctional oxygen electrocatalytic activity and ZAB performance, on the other hand, are measured in terms of potential gap between the ORR and OER, ΔE = Ej10OER - E1/2ORR, specific capacity, peak power density, open circuit voltage, voltaic efficiency, and charge-discharge cycling stability. The nonprecious metal electrocatalyst-based ZABs are very promising and they deliver high power density, specific capacity, and round-trip efficiency. The active site for oxygen electrocatalysis and challenges associated with carbon support is briefly addressed. Despite the considerable progress made with the emerging electrocatalysts in recent years, several issues are yet to be addressed to achieve the commercial potential of rechargeable ZAB for practical applications.

Advanced Oxygen Electrocatalyst for Air-Breathing Electrode in Zn-Air Batteries.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/smsc.202100012

Metal Chalcogenides with Heterostructures for High-Performance Rechargeable Batteries

To design heterojunction electrocatalysts for water splitting in industrial plants, replacing RuO 2 , IrO 2 , and Pt/C remains challenging. We prepared heterostructures of nickel selenide (NiSe) and cobalt-iron layer double hydroxide (CoFe LDH), CoFe LDH@NiSe, using hydrothermal and electrodeposition processes. The interfacial coupling enhanced the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). The CoFe LDH@NiSe required an overpotential of 127 mV and 38 mV for a current density of 10 mA cm −2 with a Tafel slope of 37 mV dec −1 and 33 mV dec −1 for OER and HER in alkaline solutions. Density functional theory calculations showed the enhancement of OER performance. The catalytic activity of CoFe LDH@NiSe increased the electronic conductivity, enhancing the water splitting with 10 mA cm −2 at 1.51 V. The robustness was demonstrated by the long-term stability for 120 h. This study provides a strategy for developing heteronanostructure electrocatalysts for water splitting in fields such as metal-air batteries and energy storage. An interface engineering approach was developed to fabricate NiSe coupled with CoFe LDH in which the hierarchical assembly of heteronanostructured nanosheets exhibited excellent electrocatalytic performance for overall water splitting kinetics. • CoFe-LDH@NiSe nanosheets were prepared by hydrothermal/electrodeposition method. • The mass activity of CoFe-LDH@NiSe surpasses the state-of-the-art electrocatalysts. • DFT proves abundant vacant active sites enhancing the performance of OER. • The designed heteronanostructure exhibits an excellent catalytic performance. 

Designing a smart heterojunction coupling of cobalt-iron layered double hydroxide on nickel selenide nanosheets for highly efficient overall water splitting kinetics

Metal-organic frameworks-derived CoP anchored on MXene toward an efficient bifunctional electrode with enhanced lithium storage

The development of low‐cost multifunctional electrocatalysts with high activity for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) is critical for the advancement of sophisticated energy conversion and storage devices. Herein, a trifunctional Ni(S0.51Se0.49)2@NC catalyst is designed and fabricated using a dianionic regulation strategy. Synchrotron radiation X‐ray absorption spectroscopy and density functional theory calculations reveal that simultaneous sulfidation and selenization can induce the electronic delocalization of Ni(S0.51Se0.49)2 active sites to enhance the adsorption of *OOH/*OH intermediate for ORR/OER and H* intermediate for HER. The OER and HER mechanisms are revealed by in situ Raman spectroscopy. The Ni(S0.51Se0.49)2@NC exhibits trifunctional catalytic activity for the HER (111 mV at 10 mA cm−2), OER (320 mV at 10 mA cm−2), and ORR (half‐wave potential of 0.83 V). The rechargeable zinc–air batteries (ZABs) exhibit an open‐circuit voltage of 1.46 V, a specific capacity of 799.1 mAh g−1, and excellent stability for 1000 cycles. The water electrolytic cell using Ni(S0.51Se0.49)2@NC electrodes delivers a current density of 10 mA cm−2 at a cell voltage of 1.59 V, and it can be powered using the constructed ZABs. These findings contribute to developing low‐cost and efficient non‐noble metal multifunctional catalysts.

Dianion Induced Electron Delocalization of Trifunctional Electrocatalysts for Rechargeable Zn–Air Batteries and Self‐Powered Water Splitting

Developing a low cost, high performance, and durable bifunctional catalyst to boost the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for water splitting is a critical yet challenging task. Transition metal phosphides have been identified as promising dual functional catalysts recently. Herein, we report a facile strategy to construct a heterostructure catalyst by integrating cobalt phosphide with molybdenum carbide (MXene). The CoP/Mo2CTx (T is the surface terminal group) catalyst exhibited good HER activity with an overpotential of 78 mV at a current density of 10 mA cm−2, close to that of the Pt/C benchmark, and its OER performance is markedly better than that of the RuO2 benchmark, evidenced by a very small overpotential of 260 mV at 10 mA cm−2 in 1 M KOH. Impressively, when employed for overall water splitting, CoP/Mo2CTx also outperformed the Pt/C + RuO2 combination with a voltage of 1.56 V @ 10 mA cm−2. Density functional theory (DFT) calculations revealed that CoP/Mo2CTx has appropriate water adsorption especially the optimal H* adsorption free energy (ΔGH*), and the Mo2C MXene support can significantly increase the total density of states and downshift the d-band center for the HER, while for the OER, multiple characterization techniques of CoP/Mo2CTx post the OER test show that CoP in the catalyst can be transformed into Co–OOH during the electrocatalytic process. This study can provide a pathway for the design and fabrication of MXene-supported noble-metal-free bifunctional catalysts toward practical water splitting and energy conversion.

Cobalt phosphide supported by two-dimensional molybdenum carbide (MXene) for the hydrogen evolution reaction, oxygen evolution reaction, and overall water splitting

Selenide/sulfide heterostructured NiCo2Se4/NiCoS4 for oxygen evolution reaction, hydrogen evolution reaction, water splitting and Zn-air batteries

Rational design of Ru aerogel and RuCo aerogels with abundant oxygen vacancies for hydrogen evolution reaction, oxygen evolution reaction, and overall water splitting

NiFe layered double hydroxide (NiFe-LDH) is cost-effective and active catalyst for oxygen evolution reaction (OER), yet further promoting its OER performance is an ongoing challenge. Herein, we devised a facile...

Zongshan Lin

Papers

Cobalt phosphide supported by two-dimensional molybdenum carbide (MXene) for the hydrogen evolution reaction, oxygen evolution reaction, and overall water splitting

Selenide/sulfide heterostructured NiCo2Se4/NiCoS4 for oxygen evolution reaction, hydrogen evolution reaction, water splitting and Zn-air batteries

Rational design of Ru aerogel and RuCo aerogels with abundant oxygen vacancies for hydrogen evolution reaction, oxygen evolution reaction, and overall water splitting

Probing the Co Role for Promoting OER and Zn-Air Battery Performance of NiFe-LDH: A Combined Experimental and Theoretical Study