The hydrogen evolution reaction (HER) is a half-cell reaction in water electrolysis for producing hydrogen gas. In industrial water electrolysis, the HER is often conducted in alkaline media to achieve higher stability of the electrode materials. However, the kinetics of the HER in alkaline medium is slow relative to that in acid because of the low concentration of protons in the former. Under the latter conditions, the entire HER process will require additional effort to obtain protons by water dissociation near or on the catalyst surface. Heterostructured catalysts, with fascinating synergistic effects derived from their heterogeneous interfaces, can provide multiple functional sites for the overall reaction process. At present, the activity of the most active known heterostructured catalysts surpasses (platinum-based heterostructures) or approaches (noble-metal-free heterostructures) that of the commercial Pt/C catalyst under alkaline conditions, demonstrating an infusive potential to break through the bottlenecks. This review summarizes the most representative and recent heterostructured HER catalysts for alkaline medium. The basics and principles of the HER under alkaline conditions are first introduced, followed by a discussion of the latest advances in heterostructured catalysts with/without noble-metal-based heterostructures. Special focus is placed on approaches for enhancing the reaction rate by accelerating the Volmer step. This review aims to provide an overview of the current developments in alkaline HER catalysts, as well as the design principles for the future development of heterostructured nano- or micro-sized electrocatalysts.

Water electrolysis operating in alkaline environments is a promising route to produce H2 on a massive scale. In this context, designing highly‐active and low‐cost electrocatalysts is of great importance. Here NiPt alloys with plenty of atomically dispersed Pt at the edges to boost hydrogen evolution in alkaline solution are reported. The formed Ni‐Pt atomic pairs at the edges hold engineered electronic structures by reducing the number of coordination atoms to facilitate the kinetically sluggish Volmer step, and further promote the hydrogen coupling step by providing separate active sites as well. With a Pt content of 3at%, this catalyst records an ultralow overpotential of 6 mV to reach the current density of 10 mA cm−2, and delivers a current density of 68.3 mA cm−2 at the overpotential of 30 mV, exceeding that of the commercial 20wt% Pt/C catalyst by a factor of >4. The aberration‐corrected transmission electron microscopy and quasi‐operando X‐ray absorption fine structure measurements show Ni‐Pt atomic pairs serve as active sites and enable the subtle adsorption/desorption balances between various intermediates (OH* and H*) during the hydrogen evolution reaction. The as‐made alloys show high stability with negligible activity decay after a 12 h chronoamperometric test, addressing its feasibility in an overall water‐splitting cell.

Catalytic mechanisms and activity trend of Ni-based heterostructures were revealed by combining experimental data and theoretical calculation results.

Given that currently more high-efficiency photocatalysts are needed to address environmental pollution, this paper has proposed an effective method of P123-modified synthesis of BiOCl nanosheet/bismuth nitrate (BiOCl/BBN) heterojunctions. The photocatalytic results showed that the BiOCl nanosheet with BiOCl/BBN heterojunctions (BOC-1) exhibited 100% efficiency in the photocatalytic degradation of RhB within 3 min under visible light, simultaneously demonstrating beneficial stability and recyclability. The effectiveness of the photocatalytic activity of BOC-1 was ascribed to the formation of BiOCl/BBN heterojunctions and P123 modification, which facilitated the separation of carriers. This study offers a convenient and effective approach for the synthesis of high-efficiency heterogeneous photocatalysts for the removal of environmental pollutants.

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