The crystalline phase plays a crucial, yet not well-understood, role in enhancing the oxygen evolution reaction (OER) performance of iron oxyhydroxide (FeOOH) materials. Herein, single-phase (α-, β-, and δ-) and mixed-phase (α/β-, α/δ-, and β/δ-) FeOOH nanostructures have been successfully synthesized through a controlled solvothermal route. Combined analyses of X-ray photoelectron spectroscopy and partial density of state calculation suggest that rich oxygen vacancies confined in the mixed-phase FeOOH samples (with optimized electronic structure) can effectively improve the OER activity. Notably, the mixed phase of β/δ-FeOOH displays an enhanced OER activity and stability in the alkaline media, with a very low overpotential of ∼180 mV vs a reversible hydrogen electrode at 10 mA cm–2. Understanding of the phase-induced activity may also pave a pathway for the design and synthesis of highly efficient electrocatalysts.

Electron density modulation is of great importance in an attempt to achieve highly active electrocatalysts for the oxygen evolution reaction (OER). Here, the successful construction of CuO@CoOOH p-n heterojunction (i.e., p-type CuO and n-type CoOOH) nanoarray electrocatalyst through an in situ anodic oxidation of CuO@CoS x on copper foam is reported. The p-n heterojunction can remarkably modify the electronic properties of the space-charge region and facilitate the electron transfer. Moreover, in situ Raman study reveals the generation of SO 4 2− from CoS x oxidation, and electron cloud density distribution and density functional theory calculation suggest that surface-adsorbed SO 4 2− can facilitate the OER process by enhancing the adsorption of OH − . The positively charged CoOOH in the space-charge region can significantly enhance the OER activity. As a result, the CuO@CoOOH p-n heterojunction shows significantly enhanced OER performance with a low overpotential of 186 mV to afford a current density of 10 mA cm −2 . The successful preparation of a large scale (14 × 25 cm 2 ) sample demonstrates the possibility of promoting the catalyst to industrial-scale production. This study offers new insights into the design and fabrication of non-noble metal-based p-n heterojunction electrocatalysts as effective catalytic materials for energy storage and conversion.

In this study, low-crystalline CoOOH nanosheet arrays that are grown on carbon fiber cloth (LC-CoOOH NAs/CFC) were prepared using a facile electrochemical strategy for the oxygen evolution reaction (OER). The lowcrystalline CoOOH nanosheets were assembled randomly by numerous short-range (1−5 nm) ordered grains with different orientations, inducing abundant grain boundaries (edge sites of CoOOH). Moreover, a certain number of structural defects (oxygen vacancies) were also engineered on the low-crystalline CoOOH nanosheets. Benefiting from these abundant edge sites of CoOOH and oxygen vacancies, LC-CoOOH NAs/CFC exhibit much improved OER activity compared to the high-crystallinity CoOOH NAs/CFC with a perfect structure. This research provides a new way to synthesize the defective materials with a short-range ordered structure and lays a valuable theoretical foundation for the structure and property of OER catalysts.

The development of low‐cost, high‐performance, and stable electrocatalysts for the sluggish oxygen evolution reaction (OER) in water splitting is essential for renewable and clean energy technologies. Herein, the interconnected nanoarrays consisting of Co–Ni bimetallic metaphosphate nanoparticles embedded in a carbon matrix (Co2−xNixP4O12‐C) are fabricated through a mild phosphorylating process of cobalt–nickel zeolitic imidazolate frameworks (CoNi‐ZIF). Density functional theory calculations reveal moderate adsorption of oxygenated intermediates on the doping Ni site, and current density simulations imply homogeneous and higher current density due to the morphology integrity of the interconnected metaphosphate nanoarrays. As a consequence, the optimized Co1.6Ni0.4P4O12‐C affords a superior OER activity (η = 230 mV at 10 mA cm−2) and long‐term stability in alkaline media (1 m KOH) that are comparable to most reported catalysts. The strategy for balancing the doping effect and morphology effect provides a new perspective when designing and developing highly efficient electrocatalysts for energy conversion and storage applications.

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