Correlating composition and electronic effects of self-assembled PtMo electrocatalysts for ethylene glycol oxidation: An experimental and theoretical approach

In recent years, there has been an increasing interest in using small organic molecules to convert chemical fuels into electrical energy. In this context, ethylene glycol (EG) is a potential feedstock due to its high energy density, which makes this molecule suitable for direct alcohol fuel cells. Thus, combining Pt atoms with other oxophilic elements, such as Mo, is a promising strategy based on the unrivaled importance of developing efficient electrocatalysts for this application. Herein, we report the engineering of PtMo nanoparticles (NPs) as the active phase for EG electrooxidation. Interestingly, a self-assembly process occurred during their manufacturing, and a simple NPs synthesis process (a modified one-pot polyol method) afforded nanostructures with virtually all Mo atoms inside the particles for different PtMo ratios. By preparing three PtMo ratios, we obtained the following NPs sizes: 2.74 ± 2.34 nm (Pt90Mo10), 2.16 ± 1.92 nm (Pt80M20), and 2.47 ± 2.09 nm (2.47 ± 2.09 nm). After immobilizing the NPs onto Vulcan XC-72 carbon black, we got different onset potentials/current densities (at 25 °C): Pt90Mo10/C (0.33 V/189.0 μA/cm2), Pt80Mo20/C (0.19 V/132.0 μA/cm2), and Pt70Mo30/C (0.24 V/95.0 μA/cm2) for the EG electrooxidation. However, essential understandings were raised regarding the studied systems: density-functional tight-binding-based (DFTB) calculations addressed the configuration of the metals in the obtained nanostructures; also, such an approach brought insights regarding the emergence of electronic properties of the different PtMo ratios and mechanistic insights corroborating analytical analyses performed by liquid chromatography. Hence, the best results could be attributed to tailored electronic effects based on a Mo-optimized quantity (Pt80Mo20/C electrocatalyst). Therefore, we believe we cooperated in better understanding PtMo-based systems, and how the metal ratio decisively can affect their performance, opening new opportunities for practical fuel cell applications.