WOx nanoparticles coupled with nitrogen-doped porous carbon toward electrocatalytic N2 reduction.

The electrocatalytic nitrogen reduction reaction (eNRR) is a sustainable and green alternative to the traditional Haber-Bosch process. However, the chemical inertness of nitrogen gas and the competitive hydrogen evolution reaction significantly limit the catalytic performance of eNRR. Although tungsten oxide-based eNRR catalysts could donate unpaired electrons to the antibonding orbitals of N2 and accept lone electron pairs from N2 to dissociate NN triple bonds, the low electrical conductivity and the influence of the variable valence of W still affect the catalytic activity. Herein, a high-performance eNRR catalyst WOx nanoparticle/nitrogen-doped porous carbon (WOx/NPC) was prepared by a one-step thermal pyrolysis method. The results reveal that WOx gradually changes from the dominant WO2 phase to the WO3 phase. WOx/NPC-700 °C with WO2 NPs anchored on the surfaces of NPC via W-N bonding could deliver a high NH3 yield of 46.8 µg h-1 mg-1 and a high faradaic efficiency (FE) of 10.2%. The edge W atomic site on WOx/NPC is demonstrated to be the active center which could activate a stable NN triple bond with an electron-donating ability. Benefiting from the covalent interaction between the WOx nanoparticles and NPC, WOx/NPC also shows high electrocatalytic stability.

NaCl template-assisted construction of a CoP-MoP heterostructured electrocatalyst for electrocatalytic nitrogen reduction.

The electrocatalytic nitrogen reduction reaction (NRR) to ammonia is a promising technology to store renewable energy and mitigate greenhouse gas emissions. However, it usually suffers from low ammonia yield and selectivity because of the lack of efficient electrocatalysts. Herein, we report that the construction of metal phosphide heterojunctions is an efficient strategy for NRR activity enhancement. A CoP-MoP heterojunction electrocatalyst, which is fabricated by a facile NaCl template-assisted strategy, exhibits a favorable ammonia yield rate of 77.8 µg h-1 mgcat-1 (38.9 µg h-1 cm-2) and a high faradaic efficiency of 11.16% at -0.50 V versus the reversible hydrogen electrode. The high NRR electrocatalytic activity can be attributed to the electronic coupling effects and interfacial synergistic effects of CoP and MoP at the heterojunction interface, which accelerates the electron transfer rate. Moreover, Mo doping changes the d-band centers of metal sites on the CoP surface, which is conducive to N2 adsorption and promotes N2* adsorption in the competition of occupying active sites, thus inhibiting the HER. This work manifests the high potential of phosphide electrocatalysts and opens an alternative route toward NRR electrocatalysis.