Formic acid oxidation is an important electrocatalytic reaction in proton-exchange membrane (PEM) fuel cells, in which both active sites and species adsorption/activation play key roles. In this study, we have developed hollow Pd-Ag alloy nanostructures with high active surface areas for application to electrocatalytic formic acid oxidation. When a certain amount of Ag is incorporated into a Pd lattice, which is already a highly active material for formic acid oxidation, the electrocatalytic activity can be significantly boosted. As indicated by theoretical simulations, coupling between Pd and Ag induces polarization charges on Pd catalytic sites, which can enhance the adsorption of HCOO^* species. As a result, the designed electrocatalysts can achieve reduced Pd usage and enhanced catalytic properties at the same time. This study represents an approach that simultaneously fabricates hollow structures to increase the number of active sites and utilizes interatomic interactions to tune species adsorption/activation towards improved electrocatalytic performance.

A Z-scheme is a promising approach to achieve broad-spectrum photocatalysis. Integration of TiO₂ with another semiconductor with a band gap of ~1.0 eV would be ideal to harvest both ultraviolet and visible-near infrared light for photocatalysis; however, most narrow-bandgap semiconductors have straddling band structure alignments with TiO₂, constituting an obstacle to forming the Z-scheme for photocatalytic hydrogen production. In this communication, we demonstrate Ag₂S as a model system where the energy band upshift of the narrow-bandgap semiconductor that shares an interface with a metal can overcome this limitation. To fabricate the design, we developed a unique approach to synthesize Ag₂S–Ag–TiO₂ hybrid structures. The obtained ternary hybrid structures exhibited dramatically enhanced performance in photocatalytic hydrogen production under full-spectrum light illumination. The activities were significantly higher than the sum of those of Ag₂S–Ag–TiO₂ structures under λ < 400 nm and λ > 400 nm irradiation as well as those of their counterparts under any light illumination conditions.