Ammonia is a promising liquid-phase carrier for the storage, transport, and deployment of carbon-free energy. However, the realization of an ammonia economy is predicated on the availability of green methods for the production of ammonia powered by electricity from renewable sources or by solar energy. Here, we demonstrate the synthesis of ammonium from nitrate powered by a synergistic combination of electricity and light. We use an electrocatalyst composed of gold nanoparticles, which have dual attributes of electrochemical nitrate reduction activity and visible-light-harvesting ability due to their localized surface plasmon resonances. Plasmonic excitation of the electrocatalyst induces ammonium synthesis with up to a 15× boost in activity relative to conventional electrocatalysis. We devise a strategy to account for the effect of photothermal heating of the electrode surface, which allows the observed enhancement to be attributed to non-thermal effects such as energetic carriers and charged interfaces induced by plasmonic excitation. The synergy between electrochemical activation and plasmonic activation is the most optimal at a potential close to the onset of nitrate reduction. Plasmon-assisted electrochemistry presents an opportunity for conventional limits of electrocatalytic conversion to be surpassed due to non-equilibrium conditions generated by plasmonic excitation.

Buckypapers made with CNx nanotubes.

The oxygen reduction reaction (ORR) is of paramount interest, in the context of both alternative energy applications in fuel cells and for on‐site hydrogen peroxide (H2O2) production in environmental remediation applications. Using theoretical and experimental methods, the mechanism involved in the ORR is studied on nitrogen‐doped graphitic carbon materials. The two principal reaction pathways involved in the ORR are the four‐electron pathway producing water (H2O), or the two‐electron pathway leading to the formation of H2O2. An atomistic step by step ORR mechanism is proposed to understand the selectivity of the reaction toward the two principal pathways. The results show that graphitic N sites favor the two‐electron pathway, in a similar way to three pyridinic N sites. Meanwhile, the one or two pyridinic N sites lead to the four‐electron pathway. The calculations show the importance of dangling bonds and/or pentagonal C rings in selectivity toward the four‐electron pathway. The results are consistent with recent reports on the importance of topological defects in graphitic carbon materials. The understanding of the ORR mechanism is very important for the design and development of novel ORR electrocatalysts to favor the required pathway, according to the application.

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