ARTICLE This journal isDeep eutectic solvents (DES) are being increasingly used in electrodeposition as it is considered as environmentally benign. We report here, a single step method for the preparation of Au-Pd core-shell nanoparticles (Au@Pd NPs) on a graphite rod in a DES medium. These ready to use mesoporous substrates were prepared by simultaneous electrodeposition of the insitu formed Au@Pd nanoparticles via anodic dissolution technique. The fabrication strategy by anodic dissolution in a DES avoided the addition of external stabilizers, reducing agents and metal salt precursors. The core-shell morphology of the nanoparticles was characterized by SEM while the elemental composition was confirmed by EDAX and cyclic voltametry. The catalytic characteristics of the Au@Pd nanoparticle modified graphite were systematically studied in the electrochemical oxidation of methanol by cyclic voltametry, Tafel analysis and activation energy measurements. The Au@Pd NPs exhibited superior catalytic performance over its corresponding monometallic counterparts viz., AuNPs and PdNPs prepared under identical conditions. The activation energy requirements of the Au@Pd NP modified graphite electrodes were low, making them a potential anode catalyst in alkaline media based methanol fuel cells at ambient temperatures. The method suggested here for the synthesis of mesoporous electrocatalysts is simple, effective and environmentally friendly. ARTICLE This journal is ARTICLE This journal is ARTICLE This journal is ARTICLEThis journal is

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The redox potentials of electroactive species are significantly influenced by the solvation characteristics of the medium. This is manifested in the shift of half-peak potentials with the change in the solvent medium. There have been many approaches till date, both experimental and theoretical to understand the role of molecular solvents in the peak potentials of redox species. The electrochemical studies reported here are aimed at understanding the effect of deep eutectic solvents (DESs) which is distinct from conventional solvents in terms of highly concentrated ionic composition, on the half-peak potentials of some standard redox reactions. The redox species selected for this study are distinct either in terms of their charge [Fe(CN) 6 4−/3− , Ru(NH 3 ) 6 2+/3+ , and ferrocene methanol, FcMeOH 0/+ ] or their hydrophilic/hydrophobic properties [methyl viologen and ferrocene]. The redox potentials are compared with the values obtained in the aqueous medium which is very well characterized in terms of solvent reorganization energy and freeenergy changes. The cyclic voltammetric behavior of the redox species in DES is significantly different from that of aqueous medium. The diffusion coefficients of the redox species in DES measured by EIS and cyclic voltammetry showed significant deviations from that predicted by Stokes−Einstein equation, indicating the dominant effect of Coulombic interactions within the components of DES.

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