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Hydrogen peroxide is a highly valuable chemical, and electrocatalytic oxygen reduction towards H2O2 offers an alternative method for safe on‐site applications. Generally, low‐cost hematite (α‐Fe2O3) is not recognized as an efficient electrocatalyst because of its inert nature, but it is herein reported that α‐Fe2O3 can be endowed with high catalytic activity and selectivity via the engineering of facets and oxygen vacancies. Density‐functional theory (DFT)calculations predict that the {001} facet is intrinsically selective for H2O2 production, and that oxygen vacancies can trigger the high activity, providing sites for O2 adsorption and protonation, stabilizing the *OOH intermediate, and preventing cleavage of the OO bond. The synthesized oxygen‐defective α‐Fe2O3 single crystals with exposed {001} facets achieve high selectivities for H2O2 of >90%, >88%, and >95% in weakly acidic, neutral, and alkaline electrolytes, respectively, and the H2O2 production rate reaches 454 mmol g−1cat h−1 at 0.1 V versus RHE under alkaline conditions. In an anion exchange membrane fuel cell, a maximum H2O2 production of 546.8 mmol L−1 with a high Faradaic efficiency of 80.5% is achieved. Thus, this work details a low‐cost catalyst feasible for H2O2 synthesis, and highlights the feasibility of theoretical catalyst design for practical applications. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen evolution reaction (HER) in alkaline medium is currently a point of focus for sustainable development of hydrogen as an alternative clean fuel for various energy systems, but suffers from sluggish reaction kinetics due to additional water dissociation step. So, the state‐of‐the‐art catalysts performing well in acidic media lose considerable catalytic performance in alkaline media. This review summarizes the recent developments to overcome the kinetics issues of alkaline HER, synthesis of materials with modified morphologies, and electronic structures to tune the active sites and their applications as efficient catalysts for HER. It first explains the fundamentals and electrochemistry of HER and then outlines the requirements for an efficient and stable catalyst in alkaline medium. The challenges with alkaline HER and limitation with the electrocatalysts along with prospective solutions are then highlighted. It further describes the synthesis methods of advanced nanostructures based on carbon, noble, and inexpensive metals and their heterogeneous structures. These heterogeneous structures provide some ideal systems for analyzing the role of structure and synergy on alkaline HER catalysis. At the end, it provides the concluding remarks and future perspectives that can be helpful for tuning the catalysts active‐sites with improved electrochemical efficiencies in future. [ABSTRACT FROM AUTHOR]

Direct observation of oxygen evolution reaction (OER) on catalyst surface may significantly advance the mechanistic understanding of OER catalysis. Here, we report the first real-time nanoscale observation of chemical OER on Mn 2 O 3 nanocatalyst surface using an in situ liquid holder in a transmission electron microscope (TEM). The oxygen evolution process can be directly visualized from the development of oxygen nanobubbles around nanocatalysts. The high spatial and temporal resolution further enables us to unravel the real-time formation of a surface layer on Mn 2 O 3 , whose thickness oscillation reflects a partially reversible surface restructuring relevant to OER catalysis. Ex situ atomic-resolution TEM on the residual surface layer after OER reveals its amorphous nature with reduced Mn valence and oxygen coordination. Besides shedding light on the dynamic OER catalysis, our results also demonstrate a powerful strategy combining in situ and ex situ TEM for investigating various chemical reaction mechanisms in liquid.