Nitrogen Reduction to Ammonia: Drawing a Path Toward Energy Efficiency
Authors: Tort Romain , Bagger Alexander , Westhead Olivia , Kondo Yasuyuki , Khobnya Artem , Winiwarter Anna , Davies Bethan J. V. , Katayama Yu , Yamada Yuki , Ryan Mary P. , Titirici Magda , Stephens Ifan 
Published: August 2024

Nitrogen reduction to ammonia stands amongst the hardest reactions to decarbonise, with the Haber-Bosch process dominating the market. In that regard, electrochemical ammonia synthesis can meet this unmet need, towards sustainable and decentralised production of fertilisers and carbon-neutral fuel.

On a solid electrode, only lithium and calcium have proven capable of splitting nitrogen selectively to ammonia yet.1–3 Tremendous progress has been made in just a few years, both in terms of the underpinning fundamentals4,5 or device engineering.6,7 However, these alkali metals require continuous operation at their plating potential, far beyond the equilibrium potential for ammonia synthesis (>3 V intrinsic overpotential, >70% energy losses to metal plating).7–9 This raises the following question: are such negative potentials a prerequisite to split the N2 triple bond
electrochemically?

One way to address this question is to look at new catalytic systems with lower intrinsic overpotential, which is highly challenging by nature.10 In this talk, we will provide a theory/experiment informed guide to the discovery of alternative electrochemical systems, considering energetics both from an electrode and electrolyte perspective.11 Theoretical analysis pinpoints many candidates energetically relevant to mediate ammonia synthesis, including some alkali-metals. Guided by the flourishing field of beyond-Li batteries, we will explore their chemistries through a series of ex or in situ characterisation of the electrolyte and solid-electrolyte interphase, model experiments and operando gas evolution measurements. This study will show how experimental validation of candidate catalysts requires control over not only the energetics of the electrode but the electrolyte too.

Learning from them, we will conclude on perspective towards catalytic systems with lower intrinsic overpotentials and how to achieve them experimentally. We hope to stimulate research paths towards breaking the inherent barrier of energy efficiency that nitrogen electroreduction is currently burdened with.

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(11) Tort, R.; Bagger, A.; Westhead, O.; Kondo, Y.; Khobnya, A.; Winiwarter, A.; Davies, B. J. V; Walsh, A.; Katayama, Y.; Yamada, Y.; Ryan, M. P.; Titirici, M.; Stephens, I. E. L. ACS Catal.
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Figure 1