Manipulating d-band center of bimetallic Sn-alloy coupling with carbon nanofibers for high-performance electrocatalytic production of ammonia from nitrate

The production of ammonia from electrochemical nitrate reduction reaction (NO3RR) has emerged as a highly promising approach to replace the conventional "Haber-Bosch" process, but the research progress of this field is still hindered by the absence of a structure-activity relationship for manipulating catalyst structure to promote its catalytic performance. In this study, we chose TMSn (M=Fe, Co, Ni) alloys as the models to evaluate the electronic structure and their NO3RR activity. Alloying various transition metals with Sn allows to regulate charge distribution, thereby modulating the d-band center of the catalysts and further regulating the catalytic activity of NO3RR. Density functional theory (DFT) simulation predicts that CoSn alloy, with the strongest NO3 adsorption and lowest thermodynamic energy barrier, is potentially considered as a highly efficient NO3RR catalyst. With this theoretical guidance, a series of TMSn alloy catalysts with carbon nanofiber (TMSn-CNF) as a support were synthesized via a two-step electrospinning/carbonization strategy. The CNF as a substrate ensures the excellent cycling performance. As a result, a significantly enhanced NO3RR activity with a NH3 yield rate of 42.20 mg h-1 cm-2 at -0.6 V vs. RHE is achieved on CoSn-CNF compared with NiSn-CNF (13.91 mg h-1 cm- 2), FeSn-CNF (13.81 mg h-1 cm- 2) and Sn-CNF (6.10 mg h-1 cm- 2), superior to most of the previously reported catalysts. We have further constructed an aqueous Zn-NO3 -battery using CoSn-CNF as the cathode, achieving a remarkable power density of 5.88 mW cm- 2. This battery not only generates large quantity of NH3, but also functions as an effective power source.