Why do Single-Atom Alloys Catalysts Outperform both Single-Atom Catalysts and Nanocatalysts on MXene?

Single-atom alloys (SAAs), combining the advantages of single-atom and nanoparticles (NPs), play an extremely significant role in the field of heterogeneous catalysis. Nevertheless, understanding the catalytic mechanism of SAAs in catalysis reactions remains a challenge compared with single atoms and NPs. Herein, ruthenium-nickel SAAs (RuNi_SAAs ) synthesized by embedding atomically dispersed Ru in Ni NPs are anchored on two-dimensional Ti₃ C₂ T_x MXene. The RuNi_SAA-3 -Ti₃ C₂ T_x catalysts exhibit unprecedented activity for hydrogen evolution from ammonia borane (AB, NH₃ BH₃ ) hydrolysis with a mass-specific activity (r_mass ) value of 333 L min^-1  g_Ru ^-1 . Theoretical calculations reveal that the anchoring of SAAs on Ti₃ C₂ T_x optimizes the dissociation of AB and H₂ O as well as the binding ability of H* intermediates during AB hydrolysis due to the d-band structural modulation caused by the alloying effect and metal-supports interactions (MSI) compared with single atoms and NPs. This work provides useful design principles for developing and optimizing efficient hydrogen-related catalysts and demonstrates the advantages of SAAs over NPs and single atoms in energy catalysis.