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Hydrogen production through alkaline water electrolysis holds great promise as a scalable solution for renewable energy storage and conversion. The development of non-precious metal-based electrocatalysts with low-overpotential for alkaline water electrolysis is essential to decrease the cost of electrolysis devices. Although the Ni-based and Fe-based electrocatalysts have been commercially employed in the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER), it is imperative to persistently pursue the advancement of highly efficient electrocatalysts with enhanced current density and fast kinetics. This feature article overviews the progress of NiMo HER cathodes and NiFe OER anodes in the traditional alkaline water electrolysis process for hydrogen production, including the detailed mechanisms, preparation strategies, and structure–function relationship. Moreover, recent advances of Ni-based and Fe-based electrodes in the process of novel alkaline water electrolysis, involving small energetic molecule electro-oxidation and redox mediator decoupled water electrolysis, are also discussed for hydrogen production with low cell voltage. Finally, the perspective of these Ni-based and Fe-based electrodes in the mentioned electrolysis processes is proposed. [ABSTRACT FROM AUTHOR]

Carbonaceous materials originated from electrospinning fibers with hierarchical porosity and good conductivity have attracted intensive attention in the field of electrocatalysis, especially for the oxygen reduction reaction (ORR). Large batches of fibers with uniform sizes can be easily fabricated by electrospinning technology as the precursors of carbon fibers, manifesting the potential to develop a large‐scale, low‐cost, high‐activity ORR catalyst production line for new energy devices such as fuel cells and metal–air batteries. Herein, based on a simple understanding of the ORR mechanism and electrospinning technology, those investigations on synthesizing non‐noble‐metal ORR catalysts through electrospinning in recent years are reviewed. The advantages brought by applying electrospinning technology to the preparation of ORR catalysts are briefly explained. Electrospinning fibers with specific structures for ORR catalysis obtained by innovated spinnerets are displayed. Importantly, the strategies of improving ORR performance for electrospinning fibers through substrate functionalization and active site regulation are discussed in detail. Finally, the prospects and challenges of developing electrospinning technology applied to non‐noble metal ORR electrocatalysis are proposed. [ABSTRACT FROM AUTHOR]

The pedestal of the rechargeable zinc–air battery (ZAB) is based on high‐performance bifunctional oxygen reduction/evolution reactions (ORR/OER) electrocatalysts. Herein, without any template or surfactant, in situ grown nitrogen‐doped carbon‐nanotube (NCNT)‐embedded with two phases of bimetal CoFe alloys and CoFe2O4 spinel oxide are constructed, using inexpensive materials of glucose, urea, and cobalt/iron acetates by programing the pyrolysis temperature. The obtained catalyst with optimal cobalt/iron acetates mass ratio (1:1) denoted as CoFe–CoFe2O4–NCNT not only exceeds Pt–Ru/C in terms of ORR half‐wave potentials [(0.88 vs 0.84 V versus reversible hydrogen electrode (RHE)] and limiting current densities (6.40 vs 5.40 mA cm−2), but also manifests superior OER activity with the potentials of (1.58 vs 1.67 V versus RHE) at 10 mA cm−2. Therefore, CoFe–CoFe2O4–NCNT exhibits a smaller ΔE value of (0.70 V versus RHE), surpassing that of Pt–Ru/C (0.85 V versus RHE) and shows excellent stability as well as outstanding methanol tolerance compared with the Pt–Ru/C commercial catalyst. In addition, CoFe–CoFe2O4–NCNT applied as a bifunctional air electrode in rechargeable ZAB displays a promising rechargeability performance with high‐discharge and low‐charge potentials and a relatively stable potential gap under 550 cycles, outperforming those of Pt–Ru/C. [ABSTRACT FROM AUTHOR]

Highly efficient and low‐cost bifunctional electrocatalysts for oxygen reduction and evolution reactions (ORR/OER) are central to new generation rechargeable metal–air batteries. Herein, hierarchical microspheres assembled by in situ generated Co4N nanoparticles (Co4N Nps)‐embedded nitrogen‐doped carbon nanotubes (Co4N@NCNTs) are constructed by a facile urea acid (UA)‐assisted pyrolysis of zeolitic imidazole framework (ZIF)‐67. In this strategy, the UA sharply decomposes at 440 °C to carbonaceous gases, which facilitate the nucleation of Co4N Nps for the catalytic growth of the NCNT microspheres structure from the intermediate ZIF‐67 polyhedrons. The as‐prepared Co4N@NCNTs exhibit high N content, abundant Co4N active species, high electron conductivity, and large specific area on a hierarchical micro‐mesoporous structure. Therefore, the Co4N@NCNTs not only exceed Pt/C in terms of ORR half wave potential (0.85 vs 0.83 V) and limiting current density (5.50 vs 5.20 mA cm−2), but also manifest comparable OER activity with Ru/C. In the rechargeable zinc–air battery test, the bifunctional Co4N@NCNTs show excellent performance with high discharge and low charge potentials and relatively stable voltage gap as long as 500 cycles, which greatly outperform those of commercial Pt–Ru/C. [ABSTRACT FROM AUTHOR]

Abstract: Water electrolysis provides an efficient method to produce hydrogen as clean energy source. Developing high activity electro‐catalysts towards the oxygen evolution reaction (OER) is crucial to improve the energy‐conversion efficiency of water electrolysis. In this work, heterogeneous nanostructures of NiFe hydroxide composites decorated by Ni metal were directly grown on a porous nickel foam (NF) substrate through an ultrafast electrodeposition process at a large cathodic current density of 1.5 A cm−2 within only 2 seconds. The as‐prepared Ni/NiFe (OH)x–1500 electrode offers a low OER overpotential of 240 mV at 10 mA cm−2 and 290 mV at 100 mA cm−2, a small Tafel slope of 36 mV Dec−1, which are superior to those of a commercial RuO2/Ti electrode. Moreover, Ni/NiFe (OH)x–1500 shows good stability and low cell voltage in the long‐time alkaline‐water splitting. Additionally, the Ni/NiFe (OH)x–1500 electrode also displays excellent electro‐catalytic activity toward the oxidation of hydrazine and glucose. This work provides a facile and rapid method to obtain high performance multifunctional electro‐catalysts. [ABSTRACT FROM AUTHOR]

The preparation of high-efficiency and low-cost electrocatalysts is vital to the development of green hydrogen energy. In this study, 3D NiCu electrodes with hierarchical micro-nano structure was constructed by a simple direct-write 3D printing technology and followed by the treatment of thermal oxidation - electroreduction steps. The composite structure of Cu NWs/Cu 2 O and Ni/NiO in the prepared 3D NiCu promotes the dissociation of water and the conversion of hydrogen, and the special micro-nano structure displays a large active surface area. Therefore, the 3D NiCu exhibits a low overpotential of 70 mV to deliver a current density of 10 mA cm−2. It demonstrates outstanding stability in the hydrogen evolution reaction experiment for 100 h in 1 M KOH. Overall, this research provides a pioneer of modified 3D printing to hydrogen production by water electrolysis. [Display omitted] • Bimetallic NiCu electrode was uniformly formed by direct-write 3D printing technology. • Micro-nano structure was prepared through thermal oxidation – electroreduction. • Prepared electrode show excellent HER performance in alkaline condition. [ABSTRACT FROM AUTHOR]

In this paper, we present a new efficient composite electrocatalyst, manganese dioxide-supported silver bismuthate (Ag 4 Bi 2 O 5 /MnO 2 ), for oxygen reduction reaction (ORR) in alkaline media. The new electrocatalyst was characterized with scanning electron microscope (SEM), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Electrochemical measurements indicate that the Ag 4 Bi 2 O 5 /MnO 2 composite is a very efficient electrocatalyst for ORR in alkaline media. The physical and electrochemical characterization results suggest that the high activity is ascribed to the support effects from MnO 2 and the synergetic effects among Ag 4 Bi 2 O 5 and MnO 2 . The analysis of rotating disk electrode (RDE) results shows that the ORR occurs via a four-electron pathway on the surface of the Ag 4 Bi 2 O 5 /MnO 2 electrocatalyst. This electrocatalyst was further tested in a designed zinc–oxygen (Zn–O 2 ) battery. This battery can offer a discharge time of 225 h at 120 mA cm −2 , increasing by more than 492% as compared with pure MnO 2 electrocatalyst. It demonstrates that this inexpensive Ag 4 Bi 2 O 5 /MnO 2 electrocatalyst is a viable alternative to platinum electrocatalyst for energy conversion devices. [ABSTRACT FROM AUTHOR]