Single-Atom Electrocatalysts for Water Splitting in Acidic Media

The proton exchange membrane water electrolyzer (PEMWE) is regarded as the most promising technique to convert intermittent renewable energy sources into clean and storable hydrogen through electrocatalytic water splitting. However, commercial electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are based on expensive platinum group metals (PGMs), which predominantly hinder the large-scale application of PEMWE. Single-atom electrocatalysts (SAECs) with atomic level dispersion of metal active sites can greatly minimize the usage amount of precious metals while keeping the efficient electrocatalytic activities. These advantages make SAECs attractive for their application in PEMWE. In this review, the mechanism of the HER and OER, together with general synthesis strategies of SAECs, was introduced and discussed. Subsequently, the recent development of SAECs based on (non)precious metals for acidic HER, OER, and overall water splitting is summarized, highlighted with the mechanism understanding between the electronic structure and electrocatalytic performance. Finally, the challenges and perspectives of SAECs for acidic water splitting are proposed.