Determining the role of Pd catalyst morphology and deposition criteria over large area plasmonic metasurfaces during light-enhanced electrochemical oxidation of formic acid

The use of metal composites based on plasmonic nanostructures partnered with catalytic counterparts has recently emerged as a promising approach in the field of plasmon-enhanced electrocatalysis. Here, we report on the role of the surface morphology, size, and anchored site of Pd catalysts coupled to plasmonic metasurfaces formed by periodic arrays of multimetallic Ni/Au nanopillars for formic acid electro-oxidation reaction (FAOR). We compare the activity of two kinds of metasurfaces differing in the positioning of the catalytic Pd nanoparticles. In the first case, the Pd nanoparticles have a polyhedron crystal morphology with exposed (200) facets and were deposited over the Ni/Au metasurfaces in a site-selective fashion by limiting their growth at the electromagnetic hot spots (Ni/Au–Pd@W). In contrast, the second case consists of spherical Pd nanoparticles grown in solution, which are homogeneously deposited onto the Ni/Au metasurface (Ni/Au–Pd@M). Ni/Au–Pd@W catalytic metasurfaces demonstrated higher light-enhanced FAOR activity (61%) in comparison to the Ni/Au–Pd@M sample (42%) for the direct dehydrogenation pathway. Moreover, the site-selective Pd deposition promotes the growth of nanoparticles favoring a more selective catalytic behavior and a lower degree of CO poisoning on Pd surface. The use of cyclic voltammetry, energy-resolved incident photon to current conversion efficiency, open circuit potential, and electrochemical impedance spectroscopy highlights the role of plasmonic near fields and hot holes in driving the catalytic enhancement under light conditions.