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Abstract Nitrate (NO3 ‒) pollution poses significant threats to water quality and global nitrogen cycles. Alkaline electrocatalytic NO3 ‒ reduction reaction (NO3RR) emerges as an attractive route for enabling NO3 ‒ removal and sustainable ammonia (NH3) synthesis. However, it suffers from insufficient proton (H+) supply in high pH conditions, restricting NO3 ‒-to-NH3 activity. Herein, we propose a halogen-mediated H+ feeding strategy to enhance the alkaline NO3RR performance. Our platform achieves near-100% NH3 Faradaic efficiency (pH = 14) with a current density of 2 A cm–2 and enables an over 99% NO3 –-to-NH3 conversion efficiency. We also convert NO3 ‒ to high-purity NH4Cl with near-unity efficiency, suggesting a practical approach to valorizing pollutants into valuable ammonia products. Theoretical simulations and in situ experiments reveal that Cl-coordination endows a shifted d-band center of Pd atoms to construct local H+-abundant environments, through arousing dangling O-H water dissociation and fast *H desorption, for *NO intermediate hydrogenation and finally effective NO3 ‒-to-NH3 conversion.

Dye-sensitized photocatalysis has been extensively studied for photocatalytic solar energy conversion due to the advantage in capturing long-wavelength photons with a high absorption coefficient. The rational integration of photosensitizer with semiconductor and cocatalyst to collaboratively operate in one system is highly desired. Here, we fabricate a Ni(OH)2-loaded titanate nanosheet (Ni(OH)2/H2Ti6O13) composite for high-performance dye-sensitized photocatalytic CO2 reduction. The ultrathin H2Ti6O13 nanosheets with negative surface charge provide an excellent support to anchor the dye photosensitizer, while the loaded Ni(OH)2 serves as an adsorbent of CO2 and electron sink of photoelectrons. As such, the photoelectrons derived from the [Ru(bpy)3]Cl2 sensitizer can be targeted transfer to the Ni(OH)2 active sites via the H2Ti6O13 nanosheets linker. A high CO production rate of 1801 μmol g-1 h-1 is obtained over the optimal Ni(OH)2/H2Ti6O13, while the pure H2Ti6O13 shows significantly lower CO2 reduction performance. The work is anticipated to trigger more research attention on the rational design and synthesis of earth-abundant transition metal-based cocatalysts decorated on ultrathin 2D platforms for artificially photocatalytic CO2 reduction.

Summary: Ammonia occupies a significant standing in the global economy. As a promising alternative to the energy-intensive Haber-Bosch process, electrochemical nitrogen reduction could achieve sustainable ammonia synthesis. However, the attractive alternative suffers from the bottleneck of insufficient activity and low electron selectivity. Here, we report an efficient electrocatalyst using phosphotungstic acid as platforms to anchor bismuth species on the 4-fold hollow site and anchor lithium species on the 3-fold hollow site, which reaches high ammonia yield rates of 61 ± 1 μg h−1 mgcat.−1 and Faradaic efficiencies of 85% ± 2% at −0.1 V versus reversible hydrogen electrode (RHE). Experiments and theoretical calculations reveal that the Biδ+ species can promote the activation and hydrogenation of nitrogen at adjacent unsaturated tungsten active sites, and the incorporated lithium species reduce the hydrogen reduction rate in undesired water splitting. This synergistic functionalization of bismuth and lithium species contributes to the high-efficient catalyst.