Unique nano-granular ZnCo2O4 microplate-decorated Pt/C as an efficient electrocatalyst for methanol electrooxidation

Abstract

In the context of developing highly potent materials as catalytic scaffolds for Pt/C-based catalysts for the methanol electrooxidation reaction, herein, nanogranule-assembled hierarchical ZnCo₂O₄ microplates are synthesized using a one-step hydrothermal process and coupled with Pt/C via a simple reflux method to form a uniform Pt/ZnCo₂O₄/C nanocomposite. The physicochemical characterizations of ZnCo₂O₄ confirm its high phase purity and the presence of interplate voids and nano-sized granules within the plates, imparting significant intraplate porosity within the microplates and uniform anchoring sites for Pt nanoparticles. HRTEM analyses reveal highly uniform and even-sized dispersion of Pt nanocrystallites in ZnCo₂O₄-modified Pt/C, unlike Pt/C, which exhibits random dispersion and agglomeration of Pt crystallites. Electrochemical evaluations demonstrate a distinct profile in the H_upd region for Pt/ZnCo₂O₄/C, which marks its higher electrochemically active surface area (30 cm² mg⁻¹) compared to that of Pt/C (17 cm² mg⁻¹). Methanol oxidation and CO-stripping cyclic voltammetry results show excellent current response, a five-fold mass activity of 110 mA mg_Pt⁻¹, a low Tafel slope of 181 mV dec⁻¹, lower charge transfer resistance, an I_f/I_b ratio of 1.48, and an enhanced CO electrooxidation current at relatively lower overpotentials for the ZnCo₂O₄-modified Pt/C catalyst than for Pt/C; these results can be attributed to the porous plate-like physiognomies of ZnCo₂O₄ that expose selective Pt facets, which act as host sites for OH_ads species for the removal of poisoning species. The Pt/ZnCo₂O₄/C electrocatalyst sustains 500 CV cycles, and an amperometric i–t study for 2 h, which exhibit insignificant morphological changes after long-term stability tests and displays negligible loss in the current response for the methanol oxidation reaction. Collectively, these results substantiate the superior antipoisoning capability of ZnCo₂O₄ microplates in facilitating methanol electrooxidation on Pt/C. This study demonstrates that nanostructurally engineered ZnCo₂O₄ can effectively promote the electrocatalytic performance of Pt/C in methanol electrooxidation, offering a promising and scalable approach for developing advanced electrocatalysts for direct methanol fuel cell applications.