The electrochemical N 2 reduction reaction has attracted interest as a potential alternative to the Haber−Bosch process, but a significantly low conversion efficiency and a significantly low ammonia production rate stimulate the need for alternatives. Here, we represent the electrochemical reduction of nitric oxide (NO) on a nanostructured Ag electrode in combination with a rationally designed electrolyte containing the EDTA−Fe 2+ metal complex (EFeMC), which results in an ∼100% efficiency for NH 3 with a current density of 50 mA/cm 2 at −0.165 V RHE , without any degradation in catalytic activity or product selectivity up to 120 h. Economic analysis using itemized cost estimation predicted that the synthesis of ammonia from NO reduction in an EFeMC-designed electrolyte can be market competitive at an electricity price of $0.03 kWh −1 with a current density of >125 mA/cm 2 . Therefore, this approach opens an entirely new avenue of renewable electricitydriven ammonia synthesis.

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There has been debate on whether Ni(OH) is truly catalytically active for the photo/electrocatalytic oxygen evolution reaction. In this report, we synthesized a Ni(OH) cocatalyst on a hematite photoanode and showed that, as has been proposed in other studies, the current density varies as a function of scan rate, which arises due to a photoinduced capacitive charging effect. We discovered that this photoinduced charging of Ni can be overcome by mixing cerium nitrate into the Ni precursor solution. Under illumination, the NiCeO cocatalyst on a hematite photoanode exhibited an approximately 200 mV cathodic shift in onset potential and a ∼53% enhancement in photocurrent at 1.23 V vs RHE. Material characterization by electrochemical impedance spectroscopy revealed that the Ni species create a p-n junction across the charge space region, which facilitates collection of the photogenerated holes by the cocatalyst layer, and core level X-ray photoelectron spectroscopy showed that Ce incorporated into the Ni-based cocatalyst layer may possibly induce the oxidation of the Ni species. In addition, we observed a reduction in binding energies of Ni after photoelectrochemical water splitting reactions, which suggests that the lattice oxygen of the NiCeO is consumed in the catalytic cycle, forming oxygen vacancies. The NiCeO cocatalyst, however, was incapable of passivating the surface recombination centers of the hematite photoanode, as indicated by the unaltered flat-band potential determined with Mott-Schottky analysis.

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