Electrocatalysis and Electrocatalytic Processes

Electrochemical water treatment replaces chemical inputs with electricity, allowing for fine-tuning of unit processes through control of applied current and potential. The Tarpeh Lab has developed electrochemical stripping, a novel alternative to conventional ammonia stripping that selectively isolates nitrogen based on charge (NH4+) and volatility (NH3) using electricity, a cation exchange membrane, and a gas permeable membrane. Based on continuous-flow nitrogen fluxes, transport from the cathode to the trap chamber was identified as the rate-limiting step of electrochemical stripping. Building on electrochemical stripping, we have expanded both product and pollutant portfolios. For products, we have advanced flexible electrochemical stripping with an additional circuit and chamber to enable tailored extraction of both acidic and alkaline ammonia. For pollutants, we have recently expanded to nitrate reduction toward ammonia via electrodialysis and nitrate reduction, a novel unit process that leverages changes in location and degree of applied electrochemical bias.We have also pioneered electrocatalyst-in-a-box, which enables homogenous catalysts to extract nitrate from real wastewaters, convert it to ammonia and other products, and separate these high-purity products.

Beyond novel processes, we are investigating effects of electrolyte composition and electrode reconstruction (together often referred to as microenvironment characteristics) to maximize catalysis. We are particularly interested in using separations to control aqueous speciation that influences catalytic performance. Ongoing studies for nitrate reduction include the effects of mass transport on electrolyte composition, the structure of the electric double layer, and molecular catalysts for highly selective transformations. We envision electrochemical nitrogen refineries capable of producing several wastewater-derived products from both ammonia and nitrate. In addition to electrifying the nitrogen cycle, we also study electrochemical sulfide oxidation to circularize sulfur management and electrochemical water-salt splitting to valorize desalination brine.