(Invited) Reshaping Resource Flows Via Electrochemically Driven Processes: Opportunities for Anode Co-Valorization Combined with Scalable Water and CO2 Electrolysis

Abstract

Understanding and advancing the water-energy-climate nexus is key to mitigating the immense threats of climate change and solving many of the related environmental issues we face today. Due to the rapid decrease in the cost of renewable energy, it is now practical to design devices that use renewable electrons in electrochemical processes to drive the transformation of CO2 and other waste feedstock (wastewater, food waste, biomass) into high-value products while also recovering important resources such as water, nutrients, and energy. Nevertheless, the bulk of current electrolyzer designs rely on the traditional oxygen evolution reaction (OER) to extract electrons from water, which has been expensive, location limited, high-risk, and generates low value (O2) product. In light of these limitations, several OER alternatives have been proposed to decrease energy consumption and/or generate high-value products that can offset operation costs and improve sustainability. These reactions can tackle a range of objectives including raw chemical generation (e.g.H2O2), waste oxidation, and molecule upgrade. By coupling worthwhile oxidation reactions at the anode with cathode electrosynthesis, industries can leverage existing infrastructure for purification, distribution, and waste-management, and even produce feedstock chemicals required for parallel processes housed at the same facility. Employing such co-valorization tactics can indeed address current drawbacks of the OER by increasing revenues and the value proposition of the overall process.In this presentation, we discuss state-of-the-art electrolysis processes that use alternative anode reactions to improve the economic viability and scalability of water or CO2 electrolysis. In particular, we will deliver a quantitative comparison of a wide range of inorganic and organic electron donors that be used in the anode to lower energy costs and/or produce value-added products. This includes the prospect of upgrading abundant waste streams such as N- containing urea and ammonia into green energy carriers. In addition, we assess the use of various transition-metal based and molecular catalysts and discuss the feasibility of using low-grade water sources such as seawater and wastewater as electrolytes. Through this wide-ranging analysis, we will include an example study for large-scale electrolysis in California, USA, provide long-term perspectives on OER substitutes for anode co-valorization, and deliver insight on future research directions. In the latter portion of the presentation, we will also discuss recent progress towards the development of cutting-edge integrated electrochemical-biological technologies that can be applied in diverse environmental and chemical applications including wastewater treatment, water reuse, desalination, remediation, and CO2 capture and conversion. Overall, the culmination of these studies can help guide future R&D efforts towards safe and efficient water, nutrient, and energy recovery.