A Multimetallic Single-Atom Catalyst on a Defective Graphene Support toward Methanol Oxidation and Oxygen Reduction Reactions: Density Functional Theory, Machine Learning, and Experiments.

Abstract

Multimetallic single-atom catalysts (SACs) have emerged as promising candidates for electrocatalytic reactions. However, identifying bifunctional multimetallic SACs capable of efficiently catalyzing both the oxygen reduction and methanol oxidation reactions (ORR and MOR), applicable to direct methanol fuel cells, remains challenging due to the vast compositional design space. Here, we propose a defective graphene-supported multimetallic SAC (M1M2M3M4M5-SAC) incorporating Mn, Pt, Fe, Ni, Co, and Cu for simultaneous MOR and ORR catalysis. Density functional theory (DFT) calculations along with machine learning (ML) predictions reveal that the Co active site in PtFeNiCoCu-SAC delivers the most favorable performance, exhibiting ORR and MOR overpotentials of 0.47 and 0.46 V, respectively. Guided by these insights, we synthesized PtFeNiCoCu-SAC and a nitrogen-doped sample, confirming their atomic structures using X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy (STEM). Electrochemical measurements validate the theoretical predictions: PtFeNiCoCu-SAC achieves an experimental ORR overpotential of 0.30 VRHE and a Tafel slope of 114 mV/dec at -1 mA/cm2, along with a half-wave potential of 0.86 VRHE. This catalyst also demonstrates good MOR activity, with a pronounced oxidation peak at 0.97 VRHE. Therefore, this work establishes a DFT- and ML-guided strategy for the accelerated rational design of multimetallic SACs and highlights PtFeNiCoCu-SAC as a promising bifunctional catalyst for energy-conversion applications.

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