Tuning Electrolyte Composition to Modulate Catalytic Performance in Molecularly Catalyzed Electrochemical Nitrate Reduction
Year: 2025
Type: article
Abstract: In molecular electrocatalysis, the turnover frequency (TOF) plateaus at applied potentials beyond the half-wave potential of the catalyst ( E cat /2 ), limiting the achievable catalytic rate for a given overpotential ( η ). This phenomenon remains a longstanding challenge for multielectron, multiproton reactions including the electrochemical nitrate reduction reaction (NO 3 RR), which generally requires large overpotentials for ammonia production ( η N O 3 − / N H 3 > 1.5 V). Thus, strategies to lower η N O 3 − / N H 3 while increasing TOF are needed for a more energy-efficient NO 3 RR. In this study, we investigate the molecular electrocatalyst [Co III (DIM)Br 2 ]ClO 4 (DIM = 2,3-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,3-diene), which selectivity catalyzes NO 3 RR to NH 3 . Through electroanalytical studies, we demonstrate that electrolyte pH and counteranion concentration can be synergistically tuned to lower η N O 3 − / N H 3 (up to 0.50 V) while increasing TOF (up to 5.2×). We therefore tailor electrolyte composition to achieve a TOF of (5.3 ± 0.4) s –1 at −0.13 V RHE ( η N O 3 − / N H 3 ≈ 0.85 V) in a solution of (0.01 M KBr + 80 mM KNO 3 + 2 mM [Co III (DIM)Br 2 ]ClO 4 ) adjusted to pH 11.1. This catalytic performance surpasses both the activities and overpotentials of state-of-the-art NO 3 RR molecular electrocatalysts. Our results reveal that even in complex reactions such as NO 3 RR (8 e – and 10 H + transfers to produce NH 3 ), electrolyte composition provides a simple handle for promoting catalytic performance.
Source: ACS electrochemistry.
Institution: Stanford University
Language: English
Subfield: Catalysis
Field: Chemical Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W4413847248