Introducing defects and in situ topotactic transformation of the electrocatalysts generating heterostructures of mixed‐metal oxides(hydroxides) that are highly active for oxygen evolution reaction (OER) in tandem with metals of low hydrogen adsorption barrier for efficient hydrogen evolution reaction (HER) is urgently demanded for boosting the sluggish OER and HER kinetics in alkaline media. Ascertaining that, metal–organic‐framework‐derived freestanding, defect‐rich, and in situ oxidized Fe–Co–O/Co metal@N‐doped carbon (Co@NC) mesoporous nanosheet (mNS) heterostructure on Ni foam (Fe–Co–O/Co@NC‐mNS/NF) is developed from the in situ oxidation of micropillar‐like heterostructured Fe–Co–O/Co@NC/NF precatalyst. The in situ oxidized Fe–Co–O/Co@NC‐mNS/NF exhibits excellent bifunctional properties by demanding only low overpotentials of 257 and 112 mV, respectively, for OER and HER at the current density of 10 mA cm−2, with long‐term durability, attributed to the existence of oxygen vacancies, higher specific surface area, increased electrochemical active surface area, and in situ generated new metal (oxyhydr)oxide phases. Further, Fe–Co–O/Co@NC‐mNS/NF (+/−) electrolyzer requires only a low cell potential of 1.58 V to derive a current density of 10 mA cm−2. Thus, the present work opens a new window for boosting the overall alkaline water splitting.

Large-scale H2 production from water by electrochemical water-splitting is mainly limited by the sluggish kinetics of the nonprecious-based anode catalysts for oxygen evolution reaction (OER). Here, we report layer-by-layer in situ growth of low-level Fe-doped Ni-layered double hydroxide (Ni1–x Fe x -LDH) and Co-layered double hydroxide (Co1–x Fe x -LDH), respectively, with three-dimensional microflower and one-dimensional nanopaddy-like morphologies on Ni foam, by a one-step eco-friendly hydrothermal route. In this work, an interesting finding is that both Ni1–x Fe x -LDH and Co1–x Fe x -LDH materials are very active and efficient for OER as well as hydrogen evolution reaction (HER) catalytic activities in alkaline medium. The electrochemical studies demonstrate that Co1–x Fe x -LDH material exhibits very low OER and HER overpotentials of 249 and 273 mV, respectively, at a high current density of 50 mA cm–2, whereas Ni1–x Fe x -LDH exhibits 297 and 319 mV. To study the overall water-splitting performance using these electrocatalysts as anode and cathode, three types of alkaline electrolyzers are fabricated, namely, Co1–x Fe x -LDH­(+)∥Co1–x Fe x -LDH­(−), Ni1–x Fe x -LDH­(+)∥Ni1–x Fe x -LDH­(−), and Co1–x Fe x -LDH­(+)∥Ni1–x Fe x -LDH­(−). These electrolyzers require only a cell potential (E cell) of 1.60, 1.60, and 1.59 V, respectively, to drive the benchmark current density of 10 mA cm–2. Another interesting finding is that their catalytic activities are enhanced after stability tests. Systematic analyses are carried out on both electrodes after all electrocatalytic activity studies. The developed three types of electrolyzers to produce H2, are very efficient, cost-effective, and offer no complications in synthesis of materials and fabrication of electrolyzers, which can greatly enable the realization of clean renewable energy infrastructure.

Hollow‐structured FexCo2−xP, FexCo3−xO4, and Prussian blue analogue (FeCo‐PBA) microbuilding arrays on Ni foam (NF) are derived from Co‐based metal–organic frameworks (Co‐MOF) using a simple room temperature and post‐heat‐treatment route. Among them, FexCo2−xP/NF shows excellent bifunctional catalytic activities by demonstrating very low oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) overpotentials of 255/114 mV at a current density of 20/10 mA cm−2 respectively, whereas FexCo3−xO4/NF and FeCo‐PBA/NF demand higher overpotentials. Remarkably, for water electrolysis, FexCo2−xP/NF requires only 1.61 V to obtain 10 mA cm−2. In contrast to water electrolysis, urea electrolysis reduces overpotential and simultaneously purifies the urea‐rich wastewater. The urea oxidation reaction at the FexCo2−xP/NF anode needs just 1.345 V to achieve 20 mA cm−2, which is 140 mV less than the 1.48 V potential required for OER. Moreover, the generation of H2 through urea electrolysis needs only 1.42 V to drive 10 mA cm−2.

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