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.

Using density functional theory calculations, we investigate the growth habit and structural stability of Ni₄ tetramer on TiO₂ (Ni₄/TiO₂), which acts as a representative of oxide-supported few-atom catalysts (FACs) ideally with high atomic utilization. We further analyze the structural characteristics and valence state distribution of metals of two structurally different Ni₄/TiO₂ for comparative study in catalysis, typically as hydrogen-related applications. The planar rhombic and tetrahedral Ni₄/TiO₂ feature the coordination environment of central metal atoms and the interfacial bonding from support interactions, respectively. Both structure-dependent binding characteristics and metal valence state distributions determine the active sites, catalytic activity, and reaction pathways and mechanisms in hydrogen production of the two catalysts. The planar rhombic structure exhibits high atomic utilization and outstanding catalytic activity, far exceeding those of the tetrahedral structure in this reaction. According to the atomic utilization and structure-dependent catalytic performance, we define and conceptualize the rising FACs, independent of cluster catalysts. These findings have implications for the design of suitable FACs and the creation of favorable conditions for multi-step reactions.

To elucidate the synergistic effect of dual-atom catalysts (DACs) at the microscopic level, we propose and construct a prototype heteronuclear system, CuNi/TiO₂, in which the two elements of a pair have significantly different d electron-donating abilities, as a piece in the puzzle. Using density functional theory calculations, we investigate charge-dependent configurations of Cu-Ni dimers anchored on TiO₂ by the mixing of individual constituent atoms. The d electron-donating ability determines deposition sequence and position of transition metal atoms on oxides, establishing dimer pattern and metal–support interactions. The interaction between Cu and Ni, beyond the coordination environment, predominately contributes to the synergistic effect. A complex adsorption–reduction behavior of H species on CuNi/TiO₂ is observed. The reaction mechanism and catalytic activity of CuNi/TiO₂ for hydrogen production are explored. At room temperature and high H coverages, CuNi/TiO₂ shows better performance and efficiency than Ni₁/TiO₂. Our findings provide a new understanding of the synergistic effect on structure–activity relationships of supported dimers, which would be beneficial in the future design of various DACs or even atomically dispersed metal catalysts.

Acid-stable and highly active catalysts for the electrocatalytic oxygen evolution reaction (OER) are paramount to the advancement of electrochemical technologies for clean energy conversion and utilization. In this work, based on the density functional theory (DFT) calculations, we systematically investigated the MSb₂O₆ (M = Fe, Co, and Ni) and transition metal (TM) doped MSb₂O₆ (TM-MSb₂O₆, TM = Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ir, and Pt) as potential antimonate-based electrocatalysts for the OER. The stability and OER activity of these considered electrocatalysts were systematically studied under acidic conditions. It was found that Rh-NiSb₂O₆, Pt-CoSb₂O₆, Rh-FeSbO₄, and Co-NiSb₂O₆ can serve as efficient and stable OER electrocatalysts, and their OER catalytic activities are better than that of the current state-of-the-art OER catalyst (IrO₂). Our findings highlight a family of promising antimonate-based OER electrocatalysts for future experimental verification.