Abstract
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.