Single-atom catalysts offering intriguing activity and selectivity are subject of intense investigation. Understanding the nature of single-atom active site and its dynamics under working state are crucial to improving their catalytic performances. Here, we identify at atomic level a general evolution of single atom into a near-free state under electrocatalytic hydrogen evolution condition, via operando synchrotron X-ray absorption spectroscopy. We uncover that the single Pt atom tends to dynamically release from the nitrogen-carbon substrate, with the geometric structure less coordinated to support and electronic property closer to zero valence, during the reaction. Theoretical simulations support that the Pt sites with weakened Pt–support interaction and more 5d density are the real active centers. The single-atom Pt catalyst exhibits very high hydrogen evolution activity with only 19 mV overpotential in 0.5 M H₂SO₄ and 46 mV in 1.0 M NaOH at 10 mA cm⁻², and long-term durability in wide-pH electrolytes.

The incorporation of defects, such as vacancies, into functional materials could substantially tailor their intrinsic properties. Progress in vacancy chemistry has enabled advances in many technological applications, but creating new type of vacancies in existing material system remains a big challenge. We show here that ionized nitrogen plasma can break bonds of iron-carbon-nitrogen-nickel units in nickel-iron Prussian blue analogues, forming unconventional carbon-nitrogen vacancies. We study oxygen evolution reaction on the carbon-nitrogen vacancy-mediated Prussian blue analogues, which exhibit a low overpotential of 283 millivolts at 10 milliamperes per square centimeter in alkali, far exceeding that of original Prussian blue analogues and previously reported oxygen evolution catalysts with vacancies. We ascribe this enhancement to the in-situ generated nickel-iron oxy(hydroxide) active layer during oxygen evolution reaction, where the Fe leaching was significantly suppressed by the unconventional carbon-nitrogen vacancies. This work opens up opportunities for producing vacancy defects in nanomaterials for broad applications.

Low-cost, efficient catalyst high-throughput screening is crucial for future renewable energy technology. Interpretable machine learning is a powerful method for accelerating catalyst design by extracting physical meaning but faces huge challenges. This paper describes an interpretable descriptor model to unify activity and selectivity prediction for multiple electrocatalytic reactions (i.e., O₂/CO₂/N₂ reduction and O₂ evolution reactions), utilizing only easily accessible intrinsic properties. This descriptor, named ARSC, successfully decouples the atomic property (A), reactant (R), synergistic (S), and coordination effects (C) on the d-band shape of dual-atom sites, which is built upon our developed physically meaningful feature engineering and feature selection/sparsification (PFESS) method. Driven by this descriptor, we can rapidly locate optimal catalysts for various products instead of over 50,000 density functional theory calculations. The model’s universality has been validated by abundant reported works and subsequent experiments, where Co-Co/Ir-Qv3 are identified as optimal bifunctional oxygen reduction and evolution electrocatalysts. This work opens the avenue for intelligent catalyst design in high-dimensional systems linked with physical insights.

Carbon-based single-atom catalysts (C-SACs), featuring a flexible, well-defined atomic geometry and superior electrical conductivity, have experienced a rapid development in the last decade and provided unique opportunities in selective oxygen reduction reaction (ORR) electrocatalysis via a direct 4e⁻ pathway or an alternative 2e⁻ pathway for sustainable energy conversion and chemical synthesis. This concise review summarizes recent experimental efforts aimed at tailoring selectivity and activity, and deriving progressive guidelines for catalyst design. First, the current exploration and development of synthetic methodologies of diverse C-SACs for the ORR are briefly outlined. Then we present a key overview of structure-dependent catalytic selectivity and activity properties, in particular emphasizing the microenvironment modulation of single-atom active sites from the aspects of regulating the central metal atoms, coordination environment and support properties. Besides, the dual active site enabled synergistic catalysis for breaking the conventional scaling relation is also highlighted. Finally, the current remaining challenges in C-SACs for the ORR and related perspectives are proposed to shed some light on the further developments toward industrialization in the future.