Paired photoelectrochemical conversion of CO2/H2O and glycerol at high rate

Abstract

Photoelectrochemistry holds the promise of directly converting sunlight to valuable chemical products. Photoelectrochemical (PEC) methods, however, lag behind their electrochemical counterparts in terms of current density. In this work, we demonstrate that, by using concentrated sunlight, we can achieve current densities similar to electrochemical methods, but with lower energy input. Specifically, we combined the direct PEC oxidation of glycerol with the dark hydrogen evolution or CO2 reduction in a membrane-separated continuous-flow PEC cell. We achieved over 110 mA cm−2 photocurrent density, which is at least an order of magnitude larger than those typically reported in the literature. We demonstrated that the product distribution of glycerol oxidation is notably different in PEC and electrochemical scenarios at the same current density, and the parasitic oxygen evolution reaction can be suppressed in the PEC case. This approach raises opportunities to drive complex electrochemical reactions in a more selective manner. Photoelectrocatalysis offers the potential to reduce energy demand and provide different selectivity profiles compared with electrocatalytic analogues, but current systems have shown limited rates. Here, recent advances in light concentration and gas diffusion electrodes are integrated into a photoelectrochemical system for coupled glycerol oxidation and CO2/H2O reduction with photocurrent densities above 100 mA cm−2.