Unveiling Electrode–Electrolyte Design-Based NO Reduction for NH₃ Synthesis

Abstract

The electrochemical N 2 reduction reaction has attracted interest as a potential alternative to the Haber−Bosch process, but a significantly low conversion efficiency and a significantly low ammonia production rate stimulate the need for alternatives. Here, we represent the electrochemical reduction of nitric oxide (NO) on a nanostructured Ag electrode in combination with a rationally designed electrolyte containing the EDTA−Fe 2+ metal complex (EFeMC), which results in an ∼100% efficiency for NH 3 with a current density of 50 mA/cm 2 at −0.165 V RHE , without any degradation in catalytic activity or product selectivity up to 120 h. Economic analysis using itemized cost estimation predicted that the synthesis of ammonia from NO reduction in an EFeMC-designed electrolyte can be market competitive at an electricity price of $0.03 kWh −1 with a current density of >125 mA/cm 2 . Therefore, this approach opens an entirely new avenue of renewable electricitydriven ammonia synthesis.

Green ammonia as a spatial energy vector: a review

“…It is possible for the green ammonia cost to fall if new synthesis technologies are designed which are superior to Haber-Bosch synthesis, but these receive little attention in the literature due to their low technology readiness level, as discussed in Section 1.1. 6,17,70 One key development which may signicantly reduce the cost of green ammonia, LOHCs and synthetic hydrocarbons is the technical readiness of solid oxide electrolyser cells (SOECs) for fuel production. Many papers consider SOECs to have a low technology readiness level and to be unable to handle dynamic load variations; however, Hauch et al 71 and Posdziech et al 72 both report substantial technological growth in the area in the past two years and indicate that dynamic load exibility may be possible.…”

Advances in Electrochemical Ammonia Synthesis Beyond the Use of Nitrogen Gas as a Source

“…As shown in Figure 6b, d, we ascribed the turnover as a result of the larger charge transfer coefficient ( ) in the Volmer step ( =0.89 in Volmer vs =0.56 in HNOH* NH*+H 2 O), making HER kinetically more favorable than ammonia synthesis as the potential decreases (becomes more negative). Overall, our theoretical work provides a clear explanation of the potential‐dependent selectivity trend observed in the experiments, [54] and highlights the importance of regulating potential for desired product selectivity.…”

“…The experimental j tot and FE were obtained on a nanostructured Ag electrode in PBS, taken from the Figure S24d,f in the Supporting Information of ref. [54], respectively. b) Free energy diagrams for NH 3 production at different potentials.…”

“…A recent paper reported electrochemical NORR in an EFeMC‐designed electrolyte (an NO‐capturing agent) on a nanostructured silver (Ag) electrode that showed 100 % Faradaic efficiency and partial current density of 48 mA/cm 2 for NH 4 + , corresponding to the rate of 3.6 mol m −2 h −1 (at −0.165 V vs RHE) [54] . On the other hand, when the authors employed nanostructured Ag in the absence of the EFeMC‐designed electrolyte, they observed significantly reduced partial current density of NH 4 + (current density less than 1 mA/cm 2 at −0.165 V vs RHE).…”

“…“n” is the electron transfer number for corresponding total reactions. The inset shows the partial current densities ( ) from experiment, [54] which were obtained with the equation , where is the total current density. The experimental and FE were obtained on a nanostructured Ag electrode in PBS, taken from the Figure S24d,f in the Supporting Information of ref.…”