Toward Cost-Effective Ensembles of Artificial Photosynthetic Nanoreactors for Solar Water Splitting

In 2021, the U.S. Department of Energy (DOE) announced its first Energy Earthshot on green hydrogen production, with a cost target of $1/kg within a decade. To put this value in perspective, astonishingly, at least 80% of this cost will be needed to pay for the operating expenditures alone of future utility-scale electricity from photovoltaics. This fact motivates less-expensive means than photovoltaics to generate and collect photogenerated mobile charge carriers, and/or exceedingly low capital cost electrochemical reactors operating at exceptionally low overpotentials. This latter option represents a paradigm shift from state-of-the-art electrolyzers that currently benefit from operation at high current densities, and thus relatively high overpotentials.<br/><br/>Optically thin photosynthetic nanoreactors transmit significant amounts of sunlight, and therefore each operates at a low current density. When combined with the multiplicative output of having many nanoreactors in an ensemble, detailed-balance solar-to-hydrogen energy conversion efficiencies are simulated to exceed those of optically thick photoelectrochemical designs. In efforts to attain these predicted higher efficiencies, Ensembles of Photosynthetic Nanoreactors (EPN) DOE Energy Frontier Research Center (EFRC) is performing detailed studies on the properties of state-of-the-art doped SrTiO₃ and BiVO₄ photocatalyst nanoparticles.<br/><br/>During my talk, I will share our recent collaborative discoveries in atomic-layer-deposited ultrathin oxide coatings to impart redox selectivity and materials stability, single-photocatalyst-nanoparticle photoelectrochemical behavior and mobile charge carrier properties, and atomic-level information on dopant distributions and materials interfaces obtained from electron microscopies and X-ray spectroscopies. I will also describe a new low-cost reactor design that we are developing. Collectively, our discoveries provide new design guidelines, and motivate additional basic science research pathways, for the development of stable composite materials to serve as active components in cost-effective artificial photosynthetic devices.