(Invited) Paired Photoelectrochemical Conversion of CO2/H2o and Glycerol at High Rate

Photoelectrochemistry holds the promise of directly converting sunlight to valuable chemical products since its birth over 50 years ago. Photoelectrochemical (PEC) methods, however, lag behind their electrochemical (EC) counterparts (which can be powered by a solar photovoltaic (PV) power source) in terms of current density, by orders of magnitude. In this work, we demonstrate that by integrating the recent achievements of the PV and EC communities (in terms of using concentrated sunlight and gas diffusion electrodes, respectively), we can achieve current densities similar to EC methods, but with lower energy input. Specifically, in this proof-of-concept study, we combined the direct PEC oxidation of glycerol (on a NiOOH co-catalyst-coated n-Si photoanode) with the dark hydrogen evolution (HER) or CO2 reduction (CO2R) in an anion exchange membrane (AEM) separated continuous-flow PEC cell. We achieved over 110 mA cm–2 photocurrent density under 10 Sun irradiation, which is at least an order of magnitude larger than those typically reported in the literature, for any of these PEC half reactions. We demonstrated that the product distribution of glycerol oxidation is notably different in PEC and EC scenarios at the same current density, and the parasitic oxygen evolution reaction (OER) can be suppressed in the PEC case. This approach raises new opportunities to drive electrochemical reactions with complex reaction pathways in a more selective manner even at high current densities. In the second part of my talk I will demonstrate the effect of the co-catalyst properties in tailoring the product distribution.