A new class of Co9 S8 @MoS2 core-shell structures formed on carbon nanofibers composed of cubic Co9 S8 as cores and layered MoS2 as shells is described. The core-shell design of these nanostructures allows the advantages of MoS2 and Co9 S8 to be combined, serving as a bifunctional electrocatalyst for H2 and O2 evolution.

Oxygen evolution reaction (OER) plays a vital role in many energy conversion and storage processes including electrochemical water splitting for the production of hydrogen and carbon dioxide reduction to value‐added chemicals. IrO2 and RuO2, known as the state‐of‐the‐art OER electrocatalysts, are severely limited by the high cost and low earth abundance of these noble metals. Developing noble‐metal‐free OER electrocatalysts with high performance has been in great demand. In this review, recent advances in the design and synthesis of noble‐metal‐free OER electrocatalysts including Ni, Co, Fe, Mn‐based hydroxides/oxyhydroxides, oxides, chalcogenides, nitrides, phosphides, and metal‐free compounds in alkaline, neutral as well as acidic electrolytes are summarized. Perspectives are also provided on the fabrication, evaluation of OER electrocatalysts and correlations between the structures of the electrocatalysts and their OER activities.

Ferric oxides and (oxy)hydroxides, although plentiful and low‐cost, are rarely considered for oxygen evolution reaction (OER) owing to the too high spin state (eg filling ca. 2.0) suppressing the bonding strength with reaction intermediates. Now, a facile adsorption–oxidation strategy is used to anchor FeIII atomically on an ultrathin TiO2 nanobelt to synergistically lower the spin state (eg filling ca. 1.08) to enhance the adsorption with oxygen‐containing intermediates and improve the electro‐conductibility for lower ohmic loss. The electronic structure of the catalyst is predicted by DFT calculation and perfectly confirmed by experimental results. The catalyst exhibits superior performance for OER with overpotential 270 mV @10 mA cm−2 and 376 mV @100 mA cm−2 in alkaline solution, which is much better than IrO2/C and RuO2/C and is the best iron‐based OER catalyst free of active metals such as Ni, Co, or precious metals.

Oxygen evolution reaction (OER) plays a key role in energy conversion and storage processes such as water splitting and carbon dioxide reduction. However, the sluggish kinetics caused by insufficient active surface and limited charge transfer hinder OER's wide applications. In this work, a novel selftemplating strategy for the fabrication of composite CoO-MoO 2 nanocages with enhanced OER performance is proposed. By designing a nanocage structure and incorporating conductive MoO 2 to promote both mass and charge transfer, high OER activity (η=312 mV at 10 mA/cm 2) as well as good stability in the resulting CoO-MoO 2 composite nanostructure can be achieved. This versatile synthetic strategy can also be extended to other metals (such as W) to provide greater opportunities for the controlled fabrication of mixed metal oxide nanostructures for electrochemical applications.

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Identification of active sites for oxygen evolution reaction (OER) plays a key role in the design and fabrication of high-performance cobalt-based electrocatalysts. Herein, we report the synthesis of two types of two-dimensional monometallic cobalt hydroxide nanoplates in aqueous solution for OER: α-Co(OH) with both Co and Co sites and β-Co(OH) with Co sites. Electrochemical characterization reveals that α-Co(OH) is more active than β-Co(OH) towards OER. The better activity can be attributed to the presence of Co sites in α-Co(OH), which are more active than Co sites. Our finding clarifies the contribution of the two catalytic sites and helps future rational design of high-performance OER electrocatalysts.

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