The establishment of electrocatalysts with bifunctionality for efficient oxygen evolution (OER)-and hydrogen evolution (HER)-reaction in acidic environments is a significant challenge to develop proton exchange membrane (PEM) water electrolyzers for production of clean hydrogen fuel. RuIr alloy was reckoned a promising electrocatalyst because of favorable OER performance and potential for HER. Here, we report the design of a bifunctional electrocatalyst with greatly boosted water splitting performance from doping RuIr alloy nanocrystals with transition metals that modify electronic structure and binding strength of reaction intermediates. Significantly, Co-RuIr resulted in small overpotentials of 235 mV for OER and 14 mV for HER (@ 10 mA cm -2 current density) in 0.1 M HClO 4 media. Therefore a cell voltage of just 1.52 V was needed for overall water splitting to produce hydrogen and oxygen. More importantly, for a series of M-RuIr (M = Co, Ni, Fe), the catalytic activity dependence at fundamental level on the chemical/valence states was used to establish a novel composition-activity relationship. This permits new design principles for bifunctional electrocatalysts.

A core-shell Ru@IrO x heterostructured nanocrystal was designed and constructed to be OER electrocatalyst in acidic media. Enhanced by strong charge redistribution across the core-shell heterojunction, this catalyst not only breaks the activity and stability limits of RuO 2 and IrO 2 simultaneously but also outperforms most of the known acidic OER electrocatalysts. This project offers a new idea to simultaneously enhance electrocatalytic activity and stability by inducing charge redistribution within heterostructured electrocatalysts.

Noble metals manifest themselves with unique electronic structures and irreplaceable activity toward a wide range of catalytic applications but are unfortunately restricted by limited choice of geometric structures spanning single atoms, clusters, nanoparticles, and bulk crystals. Herein, we propose how to overcome this limitation by integrating noble metal atoms into the lattice of transition metal oxides to create a new type of hybrid structure. This study shows that iridium single atoms can be accommodated into the cationic sites of cobalt spinel oxide with short-range order and an identical spatial correlation as the host lattice. The resultant Ir0.06Co2.94O4 catalyst exhibits much higher electrocatalytic activity than the parent oxide by 2 orders of magnitude toward the challenging oxygen evolution reaction under acidic conditions. Because of the strong interaction between iridium and cobalt oxide support, the Ir0.06Co2.94O4 catalyst shows significantly improved corrosion resistance under acidic conditions and oxidative potentials. This work eliminates the “close-packing” limitation of noble metals and offers promising opportunity to create analogues with desired topologies for various catalytic applications.

Copper is the only metal catalyst that can perform the electrocatalytic CO 2 reduction reaction (CRR) to produce hydrocarbons and oxygenates. Its surface oxidation state determines the reaction pathway to various products. However, under the cathodic potential of CRR conditions, the chemical composition of most Cu-based catalysts inevitably undergoes electroreduction from Cu 2+ to Cu 0 or Cu 1+ species, which is generally coupled with phase reconstruction and the formation of new active sites. Since the initial Cu 2+ active sites are hard to retain, there have been few studies about Cu 2+ catalysts for CRR. Herein we propose a solidsolution strategy to stabilize Cu 2+ ions by incorporating them into a CeO 2 matrix, which works as a self-sacrificing ingredient to protect Cu 2+ active species. In situ spectroscopic characterization and density functional theory calculations reveal that compared with the conventionally derived Cu catalysts with Cu 0 or Cu 1+ active sites, the Cu 2+ species in the solid solution (Cu-Ce-O x ) can significantly strengthen adsorption of the *CO intermediate, facilitating its further hydrogenation to produce CH 4 instead of dimerization to give C 2 products. As a result, different from most of the other Cu-based catalysts, Cu-Ce-O x delivered a high Faradaic efficiency of 67.8% for CH 4 and a low value of 3.6% for C 2 H 4 .

Although proton exchange membrane (PEM) water electrolyzers offer a promising means for generation of hydrogen fuel from solar and wind energy, in acidic environments the corresponding anodic oxygen evolution reaction (OER) remains a bottleneck. Because the activity and stability of electrocatalysts depend significantly on physicochemical properties, material surface and interface engineering can offer a practical way to boost performance. To date, significant advances have been made using a judicious combination of advanced theoretical computations and spectroscopic characterizations. To provide a critical assessment of this field, we focus on the establishment of material property− catalytic activity relationships. We start with a detailed exploration of prevailing OER mechanisms in acid solution through evaluating the role of catalyst lattice oxygen. We then critically review advances in surface and interface engineering in acidic OER electrocatalysts from both experimental and theoretical perspectives. Finally, a few promising research orientations are proposed to inspire future investigation of high-performance PEM catalysts.