Photoelectrochemical Nitrate Reduction to Ammonia on Ordered Silicon Nanowire Array Photocathodes.

As a new path to "green" ammonia production, photoelectrochemical nitrate reduction reaction (PEC NO3 RR) is investigated for the first time. An Au-decorated ordered silicon nanowire (O_SiNW) array photocathode demonstrates 95.6 % of Faradaic efficiency (FE) to ammonia at 0.2 VRHE , which represents a more positive potential than the thermodynamic reduction potential of nitrate by utilizing photovoltage. The high FE is possible because both Si and Au surfaces are inactive for competing water reduction to hydrogen. The O_SiNW array structure is favorable to promote the PEC NO3 RR relative to planar Si or randomly-grown Si nanowire, by enabling the uniform distribution of small Au nanoparticles as an electrocatalyst and facilitating the mass transport during the reaction. The results demonstrate the feasibility of PEC nitrate conversion to ammonia and would motivate further studies and developments.

Sodium-Containing Spinel Zinc Ferrite as a Catalyst Precursor for the Selective Synthesis of Liquid Hydrocarbon Fuels.

A microwave-assisted hydrothermal synthesis produces ZnFe2 O4 containing Na residue as a precursor to a CO2 hydrogenation catalyst that displays high CO2 conversion and high selectivity to liquid hydrocarbon products in the gasoline and diesel range with high olefin-to-paraffin ratios. Compared to reference catalysts derived from Fe2 O3 and a ZnO-Fe2 O3 physical mixture, the ZnFe2 O4 -derived catalyst contains well-dispersed iron particles with Zn serving as a structural promoter. A profound effect of the residual Na as an electronic promoter is also observed, which improves the selectivity for C5+ hydrocarbons and olefins. The ZnFe2 O4 -derived catalyst exhibits excellent performance in the CO2 Fischer-Tropsch reaction as it forms the active Hägg iron carbide (χ-Fe5 C2 ) phase readily through the in situ carburization of iron.