Electron-deficient cobalt nanocrystals for promoted nitrate electrocatalytic reduction to synthesize ammonia

Abstract

The Co-based electrocatalysts are promising for NO3− reduction reactions to synthesize NH3. However, NH3 yielding efficiencies over oxidation state Co compounds and electron-rich Co metal are still low due to the difficulties in simultaneously satisfying both NO3− adsorption and NHx hydrogenation. Herein, an electron-deficient Co nanocrystals is designed by interacting Co with pyridine nitrogen to promote the electrocatalytic NO3− reductions to synthesize NH3. Theoretical calculations predict that pyridine nitrogen modifications induce the electron-deficiency in Co nanoparticles, facilitating both the NO3− adsorption and energy-barrier decrease of *NH to *NH2. A pyridine nitrogen-doped carbon modified Co nanocrystals (Co/PN-C) are thus fabricated. The X-ray photoelectron and absorption near-edge spectroscopies confirm the electron-deficient state of Co metal in as prepared Co/PN-C materials. The Co/PN-C exhibits a high Faraday efficiency of 97.8 ± 2.0% toward NH3 generation, a remarkable NO3− removal efficiency of approximate 100%, and an outstanding NH3 yield rate of 109 mg h−1 cm−2 with a current density of 1.3 A cm−2. These performances are significantly higher than mostly reported Co-based electrocatalysts. In-situ Raman and Fourier-transform infrared spectra further confirm that Co/PN-C promotes NO3− adsorption and *NH hydrogenation to form NH3. This work gives effective strategy to tune electron-deficient Co nanocrystals for promoted NO3− electrocatalytic reduction to synthesize NH3.