Deep eutectic solvents (DESs) are emerging as promising electrolytes for electrochemical energy storage applications. Electroactive nitroxide-radical-containing organics can be dissolved in DESs to facilitate redox reactions; however, mechanistic know-how of their charge transfer kinetics at the electrode surface is rather limited. Here, we investigate the mechanism underlying the electrochemical oxidation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4-hydroxy-TEMPO). Using polarization measurements on a platinum rotating disk electrode and micro-electrode, we show that the anodic charge transfer coefficient ( α ) for one-electron transfer oxidations of TEMPO and 4-hydroxy-TEMPO approaches 0.9 in DES as well as in aqueous electrolytes, i.e., a significant deviation from α ≈ 0.5 expected for symmetric redox behavior. To explain this observation, a two-step oxidation mechanism is proposed wherein the nitroxide-containing species undergo fast charge transfer at an electrode surface followed by slow rate-limiting desorption of the adsorbed oxidized species. Numerical simulations are reported to characterize how the proposed two-step mechanism manifests in transient cyclic voltammetry behavior of the 4-hydroxy-TEMPO oxidation reaction, and good agreement with experiments is noted.

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Ultrathin metal layer-coated particles have potential applications in various fields, especially in electrocatalysis, where catalytic activity can be increased by shell@ core design. In this article, a synthetic method is introduced to synthesize shell@core nanoparticles, in which the selected reducing agent can be electrochemically oxidized preferentially on the core particle but not on the shell metal. Once the shell metal is deposited on the core metal, the oxidation of the reducing agent is inhibited, subsequently forming a shell@core particle with an ultrathin shell. By this method, carbonsupported shell(Pt)@core(Pd) nanoparticles with submonolayer Pt shell were synthesized using formic acid as reducing agent. Spectroscopic characterizations, X-ray photoelectron spectroscopy and energy-dispersive system, confirmed the Pt deposition. The shell@core structure of Pt@Pd was corroborated by scanning transmission electron microscopy analysis. This Pt(shell)@Pd(core) electrocatalyst was tested for electrochemical reduction of oxygen. Further, the influence of lattice parameter on the catalytic activity for oxygen reduction reaction was examined by varying the lattice parameter of Pt@Pd nanoparticles.

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The presence of gold on the surface of platinum nanoparticles can have profound effects on the activity in the electrochemical oxygen reduction reaction (ORR). In this work, the ORR activity is studied at different surface coverage of gold on two types of core–shell platinum–gold catalysts. Surface‐limited redox reaction and redox transmetalation methods are used to synthesize core–shell catalysts with varying degrees of gold coverage on their surface. Experimental results indicate that the presence of gold on the surface intrinsically decreases the ORR activity. Furthermore, the effect of the core on the activity for ORR has been studied.