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A bubble-releasing assisted pulse electrodeposition method was developed to create metallic alloy, NiFe, nanotube arrays in one step. The NiFe alloy nanotube array exhibited excellent bifunctional electrolytic activities, achieving low overpotentials of 100 mV for the hydrogen evolution reaction and 236 mV for the oxygen evolution reaction at 10 mA cm–2, both in 1 M KOH at room temperature. For overall water splitting, the NiFe alloy nanotube array delivered 10 mA cm–2 at an ultralow cell voltage of 1.58 V, among the top tier of the state-of-the-art bifunctional electrocatalysts. The NiFe alloy nanotube array also exhibited ultrastability at high current densities, experiencing only a minor chronoamperometric decay of 6.5% after a 24 h operation at 400 mA cm–2. The success of the present binder-free nanotube array-based electrode can be attributed to the much enlarged reaction surface area, one-dimensionally guided charge transport and mass transfer offered by the nanotube structure, and improved product crystallinity provided by the pulse current electrodeposition. The nanotube array structure proves to be a promising new architecture design for electrocatalysts.

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Presently, the most popular and economical commercial process of H 2 production is steam-methane reforming, which uses fossil fuels as the raw material and produces comparable amounts of CO 2 as the by-product. [1] It is definitely an environmental unfriendly and a non-sustainable H 2 production process, and development of green H 2 production is in urgent need. In this regard, renewable energy driven electrolytic water splitting has been gaining increasing popularity and is considered the most promising green H 2 production process for future hydrogen economy infrastructure. For electrolytic water splitting, H 2 is generated at cathodes from water reduction, the hydrogen evolution reaction (HER), and O 2 is generated at anodes from water oxidation, the oxygen evolution reaction (OER). To drive HER and OER at room temperature, a minimum thermodynamic cell voltage of 1.23 V is required. In practice, a cell voltage significantly higher than 1.23 V is required to overcome extra resistances existing in the water splitting system. [2] The extra cell voltage needed is the overpotential (η), which is the main target for electrocatalyst development to reduce its value for more efficient and thus more economically competitive hydrogen production for large-scale applications.Over the years, transition metals, particularly Fe, Ni, and Co based electrocatalysts, including alloys, [3] oxides, [4] phosphides, [5] sulfides, [6] etc. have been widely studied and exhibited excellent electrocatalytic performances toward water splitting reactions. Some of the metallic electrocatalysts showed excellent electrocatalytic activities for both HER and OER, and can be applied as bifunctional electrocatalysts for water splitting. Bifunctional electrocatalysts offer the advantage of material application convenience and many of them are multi-metal based materials such as NiFe and NiFeM. [7][8][9] Huang et al. fabricated NiFe nanotubes via a novel bubble-releasing assisted pulse electrodeposition method. These NiFe nanotubes exhibited outstanding bifunctional features in alkaline media with η 10 , η at 10 mA cm −2 , of 236 and 100 mV for the OER and HER, respectively. [7] Qin et al. used a hydrogen reduction method to coat NiFeMo alloy onto Ni foams, which showed impressive η 10 of 238 and 45 mV for the OER and HER, respectively. [8] Khalid et al. fabricated non-noble tri-metallic nanoparticles embedded Twinning is demonstrated to be an effective way of enhancing efficiencies of metallic catalysts toward electrolytic water splitting. Dendritic Cu possessing dense coherent nanotwin (NT) boundaries (NTCu-5nm) is successfully prepared with an organic-assisted electrodeposition at high pulse current densities. NT boundaries significantly improve electrocatalytic efficiencies and stability of NTCu-5nm over nanocrystalline Cu (NCCu), reducing overpotentials at 10 mA cm −2 for the oxygen evolution reaction (OER) from 378 to 281 mV and from 235 to 88 mV for the hydrogen evolution reaction (HER), with a small chronoamperometric decay of 5% after 100 ...

A simple one-step passivator-modulated nickel foam (NF) anodization process was developed to fabricate synergistically well-mixed NiO/α-Fe 2 O 3 @NF, which was demonstrated a high efficiency electrocatalyst for oxygen evolution reaction (OER), exhibiting ultralow overpotentials and excellent stability at high current densities. The NiO/α-Fe 2 O 3 @NF composite electrode, with NiO and α-Fe 2 O 3 well-mixed at nanoscale for much enhanced synergistic effects, exhibited extraordinary electrochemical activities with ultralow overpotentials of 244 and 334 mV at current densities of 50 and 500 mA/ cm 2 , respectively, for the OER in 1 M KOH. The NiO/α-Fe 2 O 3 @NF composite electrode was further tested as both the cathode and anode for overall water splitting, and achieved low working cell voltages of 1.76 and 1.99 V at the current densities of 50 and 500 mA/ cm 2 , respectively, outperforming the pairing of Pt/C@NF and IrO 2 @NF, 1.79 and 2.08 V, correspondingly. The stability of the NiO/α-Fe 2 O 3 @NF electrode was also outstanding, experiencing only a minor chronoamperometric decay of 5.6% after a continuous operation at 500 mA/cm 2 for 24 h. The success of the present catalyst design was attributed to the strong positive synergistic effects between the well mixed NiO and α-Fe 2 O 3 at nanoscale and between the nonconductive mixed oxide catalyst and the conductive nickel foam support.