Unique nano-granular ZnCo2O4 microplates decorated with Pt/C as efficient electrocatalyst for methanol electrooxidation

Abstract

In the context of developing highly potent materials as catalytic scaffolds in Pt/C based catalysts for methanol electro-oxidation reaction, herein, nano-granules assembled hierarchical ZnCo2O₄ microplates have been synthesized using one-step hydrothermal process and coupled with Pt/C adopting simple reflux method to form a uniform Pt/ZnCo2O₄/C nanocomposite. The physicochemical characterizations of ZnCo2O₄ confirm high phase purity, the presence of inter-plate voids, nano-sized granules within the plates imparting significant intra-plate porosity within the microplates and uniform anchoring sites for Pt nanoparticles. The 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. The electrochemical evaluations demonstrate a distinct profile in the Hupd region for Pt/ZnCo2O₄/C, which marks its higher electrochemically active surface area of 30 cm² mg⁻¹ compared to 17 cm² mg⁻¹ for Pt/C. The methanol oxidation and CO-stripping cyclic voltammetry results show excellent current response, five-fold mass activity of 110 mA mg_Pt⁻¹, low Tafel slope of 181 mV dec⁻¹, lower charge transfer resistance, I_f/I_b ratio of 1.48, and enhanced CO electro-oxidation current at relatively lower overpotential for ZnCo2O₄-modified Pt/C catalyst than Pt/C, which are attributed to porous-plate physiognomies of ZnCo2O₄ that expose selective Pt facets, which cater as host sites for OH_ads species for removal of poisoning species. The Pt/ZnCo₂O₄/C electrocatalyst sustained 500 CV cycles and amperometric i-t study for 2 h, insignificant morphological changes after long-term stability tests and displays negligible loss in the current response for 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 ascendable approach for developing advanced electrocatalysts for direct methanol fuel cell applications.