Highly Dispersed Rhodium on MXenes via Microwave Solvothermal Strategy for High-Performance Hydrogen Evolution Catalysis

This work presents a novel microwave-assisted solvothermal method for decorating nanoflakes of transition-metal carbides (MXenes) Ti3C2 and V2C with highly dispersed rhodium catalytic sites, significantly enhancing the electrocatalytic efficiency of the hydrogen evolution reaction (HER). The results indicate that microwave treatment does not significantly alter the nanoflake structure but promotes the formation of subnanometer-sized Rh catalytic sites. A combined analysis of density functional theory-calculated core-level shifts and experimental X-ray photoelectron (XPS) spectra identifies the most likely structures of the Rh catalytic centers formed through the microwave-assisted solvothermal process. Rh anchored to the oxygen-terminated MXene nanoflake surface, bonded to two or three oxygen atoms (RhOn), explains the Rh 3d XPS band with a notable chemical shift. Rh-decorated nanoflakes display superior catalytic performance in acidic, basic, and neutral media compared to pure MXenes. Turnover frequencies (TOF) suggest that the HER catalytic activity of Rh sites is comparable to or exceeds that of pure platinum surface atoms. Using rhodium catalytic site structures as an example, it is demonstrated that the mutual arrangement of the Gibbs free energy of hydrogen adsorption on the catalytic site, in cases with protonated and non-protonated terminal groups of the nanoflake, can serve as a criterion for electrocatalytic efficiency.