Pt(ii) single sites in mixed-metal ZIF-8/67 versus PtAuCo@ZIF-67 for electrocatalytic methanol oxidation in fuel cells

Abstract

This work presents an advanced method for fabricating zeolitic imidazolate framework-67 (ZIF-67) and Pt(II) single sites in mixed-metal ZIF-8/67 (Pt(II)-MM-ZIF-8/67) films at a liquid–liquid interface, where encapsulation of PtAuCo nanoalloys was achieved exclusively within ZIF-67. Four PtAuCo-based catalysts—unsupported PtAuCo, PtAuCo on reduced graphene oxide (PtAuCo/r-GO), as well as ZIF-stabilized variants (PtAuCo@ZIF-67 and Pt(II)-MM-ZIF-8/67)—were systematically compared for methanol oxidation in both acidic and alkaline media. Results demonstrate that Pt(II)-MM-ZIF-8/67 exhibits outstanding stability and catalytic performance in alkaline environments, a benefit attributed to synergistic charge modulation by Pt(II), Co²⁺, and Zn²⁺ ions. In contrast, the PtAuCo/r-GO catalyst proved most effective under acidic conditions. X-ray photoelectron spectroscopy revealed that platinum in the Pt(II)-MM-ZIF-8/67catalyst remains predominantly in the Pt(II) oxidation state, stabilized through coordination with 2-methylimidazole ligands in the metal–organic framework (MOF) structure, thereby resisting reduction to metallic Pt(0) even in reducing environments. The incorporation of multiple metal ions within the MOF matrix substantially alters the electronic properties of Pt(II), potentially reducing the activation barrier for oxidative-addition reactions and maximizing catalytic activity. Ultimately, this study provides the first effective demonstration of a platinum-based MOF with structurally integrated Pt(II) centers, highlighting the critical influence of mixed-metal frameworks in promoting electrocatalytic efficiency for energy conversion applications through precise structural and electronic engineering.