Paired Electrocatalysis: Nitrate Reduction to Ammonia Coupled with Anodic Upcycling of Biomass and Plastic Waste

Electrocatalysis is pivotal for sustainable energy conversion and the efficient production of value-added chemicals and fuels. The development of innovative and cost-effective electrocatalytic technologies is critical to addressing global energy and environmental challenges. However, conventional electrocatalytic systems often suffer from low energy efficiency (EE) as they utilize only one-half-cell reaction while the counter half-reaction is neglected, leading to increased operational costs. Paired electrocatalysis offers a synergistic strategy by coupling two value-generating complementary half-cell reactions within a single electrolytic system. This approach reduces the cell voltage, enhances EE, and improves the economic viability of the process by enabling the simultaneous production of valuable products with higher yields and faster reaction kinetics. This review highlights recent advancements in paired electrocatalysis, with a focus on the electrochemical reduction of nitrate to ammonia, paired with the anodic oxidation of small molecules derived from biomass and plastic waste. Key performance metrics and the design of integrated paired electrolyzers are also discussed. Oxidation of small molecules such as ethylene glycol, glycerol, glucose, and methanol at the anode, when coupled with nitrate reduction reaction (NO 3 RR) at the cathode, significantly lowers the required cell voltage and improves overall EE. The catalytic performance of emerging electrocatalysts, including metallenes, intermetallics, single-atom catalysts, high-entropy alloys, and metalated-covalent organic frameworks, is reviewed in the context of NO 3 RR. Despite being in the nascent stage, paired electrocatalysis holds great promise for maximizing both atom and energy economy. Faradaic efficiency approaching 100% and high conversion rates are achieved at the laboratory scale. However, translation to industrial scales mandates further research work, comprehensive techno-economic assessments, and standardized benchmarking protocols. Current analyses underscore that the strategic pairing of cathodic and anodic reactions offers a highly cost-effective and scalable alternative to conventional unpaired electrochemical processes.