Conference Agenda

Electrocatalytic water treatment has emerged into the limelight of scientific interest, yet their long-term viability remains largely in the dark. Despite the progress in materials development, little is known regarding their performance under real wastewater matrices, which contain a multitude of impurities at everchanging concentrations. In this talk, we present a comprehensive framework on how to tune the catalyst design and operating parameters to bolster impurity tolerance and overall longevity. We will first demonstrate how to rapidly identify wastewater constituents that are most detrimental to activity and selectivity. Using this information, we then explore pulsed electrolysis operation to periodically clean and regenerate the electrodes. This is further optimized by tuning the catalyst synthesis to better accommodate the pulsing sequences and minimize the extent of deactivation. Our methodical approaches improve electrode lifetimes to 300 h and 35 times that attainable under conventional operation, and they are versatile across various reactions (including H₂O₂ electrosynthesis and cathodic dechlorination). This presentation will delve into the application of these strategies, which remain critical for the development of more robust electrocatalytic technologies for water remediation.

Innovations of electrochemical carbon dioxide reduction reaction (CO₂RR) under the global awareness of CO₂ removal have prompted pioneering designs to promote carbon conversion. However, existing CO₂RR systems are operated under extreme pH environment (pH<3) and large overpotentials (>1V) to conquer the reaction barriers, posing constrains of high voltage and rapid material depletion when maintaining acceptable current densities (>100 mA/cm²). Therefore, it is vital to advance the efficiency of proton-electron utilization in CO₂RR through original theory and material innovations.

To solve this imminent challenge, our study makes breakthroughs at three folds (system profiling, reaction theory, and electrode/membrane material). Via state-of-the-art real-time K⁺-H⁺-electron sensory profiling, we obtain the first-ever system-scale mass-charge redox profiles for CO₂RR at an unprecedented spatiotemporal resolution. With such high-resolution profiles, we discover a new “proton-electron piston” theory based on proton-coupled electron transfer model (PCET), pioneeringly identify the existence of mutual driven force between electrons and protons, and unfold the electric-chemical energy conversion within the exchange membrane (EM)-electrode unit. Equipped with this groundbreaking theory, we develop a proton-promoted EM-Electrode Entity (E³) using nanometer-single-sided sulfonated polyamide cation exchange membrane and triply wedged gas diffusion electrode, which converts the cumulated non-Faradaic electrons into reductive Faradaic electrons, and thereby turns the electrochemical limitation into reaction benefit. Compared to previous studies, our innovative E³ system achieves sixfold boost of current density (298.2 mA/cm²). Our landmark discoveries can advance CO₂RR scalability and facilitate electrocatalytic system designs for broad environmental engineering applications (e.g., heavy metal recovery, value-added carbon products).

Recovering nitrogen from wastewater provides a unique opportunity to reduce harmful discharge while decreasing the dependence on Haber-Bosch fertilizer production. Selective adsorbents have the potential as a low-cost, modular technique to recover nitrogen as ammonium (NH₄⁺) from wastewaters via adsorbing onto negatively charged functional groups. Recent improvements to NH₄⁺-selective adsorbents involve modifying commercial cation exchange resins into metal-loaded ligand exchangers that adsorb via metal-ammine bond formation. Over 90% of the adsorbed ammonia was recovered after batch adsorption with acid regenerants, suggesting nitrogen-selective adsorbents could be utilized for nutrient recovery. However, metal elution at high NH₄⁺ and H⁺ concentrations can limit adsorbent effectiveness in wastewater, pose environmental risks, and exacerbate process costs. The goal of this study was to understand the operating parameters for a hybrid electrochemical ion exchange system that would minimize metal elution, maximize ammonium recovery, and reduce chemical demands compared to typical acid regeneration. We demonstrated that electro-assisted regeneration of metal-loaded ligand ion exchangers could facilitate in situ nutrient recovery using solutions from ideal ammonium salts to real urine. When comparing adsorption solutions, we observed that as the solution contained more non-NH₄⁺ cations, the recovery decreased substantially (63% reduction). Similarly, increasing the current density (1mA to 60mA) improved regeneration and recovery but resulted in higher zinc elution (<25%) across solutions. Further experiments will explore the feasibility of reforming metal-ligand bonds after elution. Our findings suggest that electro-assisted regeneration of NH₄⁺ selective adsorbents is a feasible option to enable nitrogen recovery and decrease energy consumption from conventional fertilizer production.

Selective ion separation plays a crucial role in environmental engineering and related fields. Examples include toxic ionic contaminant removal, resource recovery from various water resources, and scalant treatment for high recovery desalination. Electrochemical ion processes for ion separation have attracted increasing interest, as they can potentially be free of chemical additives and powered by renewable electricity. However, the complexity of operation schemes, particularly for newly developed processes, makes it challenging to evaluate their separation and energy efficiency. To address this challenge, we propose a theoretical framework for analyzing the thermodynamics and energy efficiency of electrochemical ion separation processes. We evaluate two prevalent electrically-driven processes, i.e., selective electrodialysis and electrosorption, with the framework. New performance metrics are formulated to assess the application of novel materials and process design. Our analysis reveals that varying applied current density results in a tradeoff between energy consumption and capital cost. Selectivity, conductivity, and scale determine the applicability of a novel material. Overall, the proposed theoretical framework provides a comprehensive evaluation of the thermodynamics and energy efficiency of electrochemical ion separation processes and offers valuable guidance for process design and material selection.

Eletrcomethanogenesis is a mechanism of methane generation by microbial biological conversion of carbon dioxide and electrical current. In this mechanism, electromethanogens can convert the waste organic materials to methane as energy supply. Therefore, the enrichment and cultivation of this group of microbes are important. Our study focuses on the enrichment environment for electromethanogens under four conditions: 1) disrupted negative potential (-0.6V vs.Ag/AgCl), 2) disrupted positive-negative pulsed potentials (+- 0.6V), 3) continuous negative pulsed potential, (-0.6V), 4) control-condition (0V). We monitored the carbon conversion via several parameters including biogas, methane gas, volatile fatty acid, soluble COD, pH, accumulative charges. Meanwhile, we collected biomass to analyze the microbiological species and abundance. The results indicated that the preferred enrichment conditions of eletromethnogens are the 2^nd and 3^rd. Under these condtions, methane is more concentrated (10 – 25%) in total gas produced than other conditions. In the last enrichment, the total gas produced from 2^nd condition is 10.3 % higher than the 3^rd condition, which had never been seen in the past four enrichment. The pH of 2^nd condition dropped periodically when positive potential applied whereas the pH of other three conditions kept at 7. And the soluble COD showed similar carbon consumption by microorganisms for all four conditions. The study provided an interesting insight on enrichment of electromethanogens during positive pulsed potentials. The application can be further used in various bioelectrode systems to boost methane production.