Environmental and economic potential of decentralised electrocatalytic ammonia synthesis powered by solar energy

Intense efforts have been devoted to developing green and blue centralised Haber-Bosch processes (gHB and bHB, respectively), but the feasibility of a decentralised and more sustainable scheme has yet to be assessed. Here we reveal the conditions under which small-scale systems (NH 3 -leaves) based on the electrocatalytic reduction of nitrogen (eN 2 R) powered by photovoltaic energy could realise a decentralised scheme competitive in terms of environmental and economic criteria. For this purpose, we calculated energy efficiency targets worldwide, providing clear values that may guide research in the incipient eN 2 R field. Even at this germinal stage, the NH 3 -leaf technology would compete favourably in sunny locations for CO 2 -related Earth-system processes and human health relative to the business-as-usual production scenario. Moreover, a modest 8% gain in energy efficiency would already make them outperform the gHB in terms of climate change-related impacts in the sunniest locations. If no CO 2 taxation is enforced, the lowest estimated ammonia production cost would be 3 times the industrial standard, with the potential to match it provided a substantial decrease of investment costs and very high selectivity toward ammonia in eN 2 R are achieved. The disclosed sustainability potential of NH 3 -leaf makes it a strong ally of gHB toward defossilised ammonia production. A planetary boundary analysis of decentralised electrocatalytic ammonia synthesis powered by solar energy reveals its potential and provides regional performance figures of merit. Conditions for economic viability are discussed.