Transition metals have been recognized as excellent and efficient catalysts for transforming gaseous molecules into value-added chemicals. Electrochemical ammonia synthesis through the atmospheric reduction of nitrogen and nitrogen oxide is a promising method for sustainable fertilizer and carbon-free hydrogen energy carriers. However, it is a great challenge to main the activity and stability of the catalyst due to its corrosive nature and vigorous reaction conditions involved in the electrochemical transformations.

We report stable core-shell electrocatalysts that utilize transition metal nanoparticles in the core and nitrogen-doped porous carbon architecture in the shell for the efficient electroreduction of N₂ and NO to ammonia (NH₃). The carbon shell prevents the dissolution of Ni nanoparticles. It ensures the long-term stability of the catalyst, whereas the Ni nanoparticles involve in the catalytic reduction of NO to NH₃ during electrolysis. The catalyst images reveal a core-shell structure composed of dark metallic spherical particles at the core and layered carbon as a shell surrounding the nanoparticles (Fig. 1a). A broad particle size distribution of 15 nm to 50 nm was observed, and the core-shell particles were interconnected by a smooth carbon matrix. The heteroatom content and the shell thickness strongly influence the catalytic activity. A high faradaic efficiency (FE) of 72.3% at 0.16 V_RHE is achieved (Fig. 1b). Moreover, the full-cell electrolyzer was constructed by coupling developed cathodes and commercial RuO­₂ as anode for oxygen evolution reaction, which delivered a stable performance over several cycles at 1.5 V. Further, we demonstrate the solar to fuel transformation by integrating with a PV-electrolyzer cell, it presented an appreciable FE of >50%.

Fig. 1. (a) TEM image of core-shell catalyst, (b) comparison of FE and NH₃ yields on various electrocatalysts for the nitric oxide reduction reaction.