Single-atom catalysts for electrocatalytic applications: Synthetic strategies, in-situ characterization, and future challenges

Emerging single-atom catalysts (SACs) show considerable promise for applications in electrocatalysis due to their exceptional structural /chemical robustness and fascinating atomic-scale exploitation performance originating from their structural tunability, potential electrocatalytic activity/ selectivity, and fabrication processes. Despite some revolutionary advances in fabrication, SACs are characterized by a low density of active sites, poor atomic dispersion, and long-term anchoring in place. The emergence of this field, such as 2D materials and transition metals, can overcome some limitations in catalytic development and lead to more homogenous and heterogeneous catalysts. Various aspects are discussed, including the potential to exceed the reaction mechanism with isolated metal atoms stabilized by such synthesis methods. This tutorial review provides a fundamental understanding of the basic mechanism, synthetic strategies, activity improvements, and future challenges. In addition, recent advances related to the SACs design and diverse utilization in electrocatalysis including carbon dioxide reduction reaction (CO2RR), nitrogen reduction reaction (NRR), oxygen reduction reaction (ORR), oxygen evolution reaction (OER) as well as hydrogen evolution reaction (HER) are summarized. We review recent progress in exceptional tunability of catalytic sites with structure prediction having the potential to explore many new and complex materials, including bonding interactions and atomic configurations. We also discuss the prospects for improving SACs activity to endow them with doping strategies, and challenges that need to be addressed in combination with theoretical calculations as well as experimental observations to achieve further progress.