Yuchun Ren

Abstract NiCo 2 O 4 nanowire array on carbon cloth (NiCo 2 O 4 /CC) is proposed as a highly active electrocatalyst for ambient nitrate (NO 3 − ) reduction to ammonia (NH 3 ). In 0.1 m NaOH solution with 0.1 m NaNO 3 , such NiCo 2 O 4 /CC achieves a high Faradic efficiency of 99.0% and a large NH 3 yield up to 973.2 µmol h −1 cm −2 . The superior catalytic activity of NiCo 2 O 4 comes from its half‐metal feature and optimized adsorption energy due to the existence of Ni in the crystal structure. A Zn‐NO 3 − battery with NiCo 2 O 4 /CC cathode also shows a record‐high battery performance.

Abstract Seawater electrolysis is an attractive way of making H 2 in coastal areas, and NiFe‐based materials are among the top options for alkaline seawater oxidation (ASO). However, ample Cl − in seawater can severely corrode catalytic sites and lead to limited lifespans. Herein, we report that in situ carbon oxyanion self‐transformation (COST) from oxalate to carbonate on a monolithic NiFe oxalate micropillar electrode allows safeguard of high‐valence metal reaction sites in ASO. In situ/ex situ studies show that spontaneous, timely, and appropriate COST safeguards active sites against Cl − attack during ASO even at an ampere‐level current density ( j ). Our NiFe catalyst shows efficient and stable ASO performance, which requires an overpotential as low as 349 mV to attain a j of 1 A cm −2 . Moreover, the NiFe catalyst with protective surface CO 3 2− exhibits a slight activity degradation after 600 h of electrolysis under 1 A cm −2 in alkaline seawater. This work reports effective catalyst surface design concepts at the level of oxyanion self‐transformation, acting as a momentous step toward defending active sites in seawater‐to‐H 2 conversion systems.

NH3 is an essential feedstock for fertilizer synthesis. Industry-scale NH3 synthesis mostly relies on the Haber-Bosch method, however, which suffers from massive CO2 emission and high energy consumption. Electrocatalytic NO3− reduction is an attractive substitute to the Haber-Bosch method for synthesizing NH3 under mild conditions. As this reaction will produce a variety of products, it highly desires efficient and selective electrocatalyst for NH3 generation. Here, we report in situ grown Fe3O4 particle on stainless steel (Fe3O4/SS) as a high-efficiency electrocatalyst for NO3− reduction to NH3. In 0.1 M NaOH with 0.1 M NaNO3, such Fe3O4/SS reaches a remarkable Faradaic efficiency of 91.5% and a high NH3 yield of 10,145 µg·h−1·cm−2 at −0.5 V vs. reversible hydrogen electrode (RHE). Furthermore, it owns robust structural and electrochemical stability. This work provides useful guidelines to expand the scope of metallic oxide electrocatalysts for NH3 synthesis. The catalytic mechanism is uncovered and discussed further by theoretical calculations.