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Abstract
Using renewable electricity to synthesize ammonia from nitrogen paves a sustainable route to making value-added chemicals but yet requires further advances in electrocatalyst development and device integration. By engineering both electrocatalyst and electrolyzer to simultaneously regulate chemical kinetics and thermodynamic driving forces of the electrocatalytic nitrogen reduction reaction (ENRR), we report herein stereoconfinement-induced densely populated metal single atoms (Rh, Ru, Co) on graphdiyne (GDY) matrix (formulated as M SA/GDY) and realized a boosted ENRR activity in a pressurized reaction system. Remarkably, under the pressurized environment, the hydrogen evolution reaction of M SA/GDY was effectively suppressed and the desired ENRR activity was strongly amplificated. As a result, the pressurized ENRR activity of Rh SA/GDY at 55 atm exhibited a record-high NH3 formation rate of 74.15 μg h-1⋅cm-2, a Faraday efficiency of 20.36%, and a NH3 partial current of 0.35 mA cm-2 at -0.20 V versus reversible hydrogen electrode, which, respectively, displayed 7.3-, 4.9-, and 9.2-fold enhancements compared with those obtained under ambient conditions. Furthermore, a time-independent ammonia yield rate using purified 15N2 confirmed the concrete ammonia electroproduction. Theoretical calculations reveal that the driving force for the formation of end-on N2* on Rh SA/GDY increased by 9.62 kJ/mol under the pressurized conditions, facilitating the ENRR process. We envisage that the cooperative regulations of catalysts and electrochemical devices open up the possibilities for industrially viable electrochemical ammonia production.
Highlights
Using renewable electricity to synthesize ammonia from nitrogen paves a sustainable route to making value-added chemicals but yet requires further advances in electrocatalyst development and device integration
Through extensive electrocatalytic nitrogen reduction reaction (ENRR) test using adequately cleaned N2, we found that the as-prepared M SA/GDY electrocatalysts render prominently enhanced ammonia electroproduction with obvious hydrogen evolution reaction (HER) inhibition at the pressurized electrocatalytic system, suggesting positive cooperation between SAC and the pressurized environment
A record-high ammonia yield rate of 74.15 μg h−1·cm−2, a Faraday efficiency (FE) of 20.36%, and a NH3 partial current density of 0.35 mA cm−2 were achieved for Rh SA/GDY at 55 atm of N2, which shows 7.3, 4.9, and 9.2-fold enhancement in comparison with those obtained in ambient conditions, outperforming the state-of-art ENRR catalysts
Summary
Using renewable electricity to synthesize ammonia from nitrogen paves a sustainable route to making value-added chemicals but yet requires further advances in electrocatalyst development and device integration. Given that the reductive N2 adsorption (N2 + e− + H+ → *N = NH) is usually regarded as the potential limiting step, novel metal single-atom catalysts (SACs, e.g., Ru, Rh, Co) with a favorable ENRR kinetics guarantee a great promise to circumvent the N2 activation energy barrier [24,25,26,27].
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