Ionic liquid (IL)-modified carbon-supported catalysts have demonstrated significant improvements in oxygen reduction reaction (ORR) activity. However, transition of this result from the half-cell to the proton exchange membrane fuel cell (PEMFC) has been challenging. Presented here is a processing methodology that yields the formation of a thin (<2 nm) conformal IL coating on the surface of both three-dimensional electrocatalysts and bulk single crystals through the sequential capacitive deposition (SCD) of anionic and cationic components and their subsequent condensation into a hydrophobic, protic IL. SCD shows promise for IL incorporation into preformed PEMFC catalyst layers.

Advances in electrocatalyst functionality have resulted from the evolution of complex nanostructured materials with increasing degrees of compositional and morphological complexity. Focused almost entirely on pushing the boundaries of intrinsic activity, electrocatalytic material development often overlooks stability. Operating in parallel to the typical mechanisms of electrochemical material degradation, three-dimensional nanomaterials are susceptible to an additional degradation process known as coarsening. Driven by the reduction of surface free energy, surface diffusion evolves the nanoporous morphology toward a solid spherical particle. Here, using nanoporous NiPt alloy nanoparticles (np-NiPt/C) as a representative three-dimensional electrocatalytic material, we demonstrate that coarsening is the dominant mechanism of degradation as observed during accelerated durability testing (ADT). The upper potential limit (UPL) of the ADT protocol is found to have a significant impact on coarsening, with the rate roughly scaling with the UPL. Here we demonstrate the viability of a methodology to limit the coarsening process by decoration of the surface with a foreign metal impurity, Ir, possessing a surface diffusivity lower than that of the catalytic species. Ir, present in a low coverage with negligible impact on the intrinsic activity, dramatically slows morphology evolution. This strategy is shown to result in significant improvements in the electrochemically active surface area and transitionmetal alloying component retention up to a UPL of 1.1 V versus the reversible hydrogen electrode. This proof-of-concept result demonstrates the utility of this strategy for improving the balance between activity and stability for three-dimensional electrocatalytic nanomaterials with potential application to a broad range of nanoscale geometries and compositions.

Hot carriers (electrons and holes) generated from the decay of localized surface plasmon resonances can take a major role in catalytic reactions on metal nanoparticles. By obtaining surface enhanced Raman scattering (SERS) spectra of p-aminothiophenol as product of the reduction of p-nitrothiophenol by hot electrons, different catalytic activity is revealed here for nanoparticles of silver, gold, and copper. As a main finding, a series of different ligands, comprising halide and non-halide species, are found to enhance product formation in the reduction reaction on nanoparticles of all three metals. A comparison with the standard electrode potentials of the metals with and without the ligands and SERS data obtained at different electrode potential indicate that the higher catalytic activity can be associated with a higher Fermi level, thereby resulting in an improved efficiency of hot carrier generation. The concept of such a ligandenhanced hot electron reduction provides a way to make light-to-chemical energy conversion more efficient due to improved electron harvesting.

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