Solar conversion to electricity or to fuels based on electron-hole pair production in semiconductors is a highly evolved scientific and commercial enterprise. Recently, it has been posited that charge carriers either directly transferred from the plasmonic structure to a neighbouring semiconductor (such as TiO₂) or to a photocatalyst, or induced by energy transfer in a neighbouring medium, could augment photoconversion processes, potentially leading to an entire new paradigm in harvesting photons for practical use. The strong dependence of the wavelength at which the local surface plasmon can be excited on the nanostructure makes it possible, in principle, to design plasmonic devices that can harvest photons over the entire solar spectrum and beyond. So far, however, most such systems show rather small photocatalytic activity in the visible as compared with the ultraviolet. Here, we report an efficient, autonomous solar water-splitting device based on a gold nanorod array in which essentially all charge carriers involved in the oxidation and reduction steps arise from the hot electrons resulting from the excitation of surface plasmons in the nanostructured gold. Each nanorod functions without external wiring, producing 5 × 10(13) H₂ molecules per cm(2) per s under 1 sun illumination (AM 1.5 and 100 mW cm(-2)), with unprecedented long-term operational stability.

Electrocatalytic reduction is a promising approach to remediate nitrate (NO3 –), one of the world’s most widespread water pollutants. In the present work, we elucidate activity and selectivity trends of transition metals for electrocatalytic nitrate reduction to benign or value-added products such as N2 and NH3. Using density functional theory (DFT) calculations, we find that the adsorption strengths of oxygen and nitrogen atoms act as descriptors for the overall activity and selectivity of nitrate reduction electrocatalysts. Nitrate reduction rates, volcano plots, surface species coverages, and the degree of rate control were predicted for transition metal electrocatalysts as a function of applied potential using DFT-based microkinetic modeling. Our microkinetic model rationalizes a number of experimental observations including the activity trends of pure metals and our in situ X-ray absorption spectroscopy measurements of competitive adsorption between hydrogen and nitrate on Pt/C. We also predict that Fe3Ru, Fe3Ni, Fe3Cu, and Pt3Ru are promising catalysts for nitrate electroreduction toward N2 with relatively high activity and selectivity. Ultimately, this work gives insight into nitrate reduction on transition metal surfaces and can guide the design of improved electrocatalysts for nitrate remediation.

Reactor and particle design considerations of particle suspension reactors for solar photoelectrochemical water splitting.