High-performance electrocatalytic CO2 reduction to CO using Ni single-atom catalyst in an anion membrane electrode assembly.

The surface electronic structures of catalysts need to be carefully engineered in CO 2 reduction reaction (CO 2 RR), where the hydrogen evolution side reaction usually takes over under a significant overpotential, and thus dramatically lowers the reaction selectivity. Surface oxides can play a critical role in tuning the surface oxidation state of metal catalysts for a proper binding with CO 2 RR reaction intermediates, which may significantly improve the catalytic activity and selectivity. Here, we demonstrate the importance of surface-bonded oxygen on silver nanoparticles in altering the reaction pathways and improving the CO 2 RR performances. A comparative investigation on air-annealed Ag (Air-Ag) catalyst with or without the post-treatment of H 2 thermal annealing (H 2 -Ag) was performed. In Air-Ag, the subsurface chemically bonded O species (O− Ag δ+ ) was identified by angle resolved X-ray photoelectron spectroscopy and X-ray absorption spectroscopy techniques, and contributed to the improved CO selectivity rather than H 2 in CO 2 RR electrolysis. As a result, though the maximal CO Faradaic efficiency of H 2 -Ag is at ∼30%, the Air-Ag catalyst presented a high CO selectivity of more than 90% under a current density of ∼21 mA/cm 2 .

Scaling up electrochemical water splitting is nowadays in high demand for hydrogen economy implementation. Tremendous efforts over the past decade have been focused on exploring alternative catalytic materials, including a variety of earth-abundant transitionmetal-based catalysts, to replace traditional noble metals such as Pt, Ir, or Ru. Nevertheless, few efforts have been carried out for (1) scalable catalyst synthesis on current collectors and (2) practical device design toward large-scale H 2 generation. Herein, we designed a modular alkaline water-splitting electrolyzer system with scaled-up metal foam electrodes covered by low-cost NiMo alloy and Ni 3 Fe oxide for efficient hydrogen evolution and oxygen evolution, respectively. An electrolyte circulation system facilitates the mass transport and thus can further boost the H 2 generation particularly under large currents. As a result, the overall water-splitting performance of one-unit cell with a dimension of 10 × 10 cm 2 under room temperature presents an early onset voltage of 1.54 V and delivered practical currents of 20 and 55 A (9.1 and 25.0 L/h H 2 generation) under 2.2 and 2.9 V without iR compensations, respectively. This demonstration could stimulate new focuses in water splitting toward more practical applications.