Roles of coordination combinations in the performance and application of Pd₁/C₃N single-atom catalysts: A design for multifunctional catalysts from first-principles

Beyond the coordination environment of single-atom catalysts (SACs), the moiety constructed by single-atom (SA) and coordination combinations is thought to play a significant role in the reaction kinetics, especially in multi-step reactions, but the mechanism is still unclear. Here we select the single Pd atom embedded C₃N monolayers (Pd₁/C₃N) as a representative class of carbon-based SACs. Using density functional theory, we investigate the synthesis conditions, structural and bonding characteristics, electronic structures and catalytic performances, and multifunctional applications of Pd₁/C₃N samples. Atomic vacancies generated under high-temperature/low-pressure allow the formation of various Pd-C_xN_y moieties on the monolayer with coordination combinations control. The Pd-C_xN_y moieties with adjustable C/N coordination combinations not only exhibit tunable hydrogen evolution activity, but also have magnetic and non-magnetic properties, indicative of a clear structure–activity relationship. The Pd₁/C₃N monolayer is demonstrated to be a promising multifunctional catalyst for electrochemical hydrogen production, photocatalytic water splitting and magnetic recycling, all of which are reliant on the roles of coordination combinations. The strategy based on coordination combinations is expected to pave the way for future development of carbon-based SACs and even few-atom catalysts for multifunctional catalysis in energy and environment.