Tandem devices for simultaneous CO2 reduction at the cathode and added-value products formation at the anode

Multi-win situation of wastewater purification, carbon emission reduction and resource utilization: Conversion of refractory organics and nitrate to urea and ammonia in a flow-through electrochemical integrated system

The advanced oxidation process is an efficient technology for the degradation and detoxification of refractory organics to ensure water safety. However, most researches focus on improving pollutant degradation but overlook carbon emission and resource utilization. In this study, a flow-through electrochemical integrated system was constructed to simultaneously realize bisphenol A (BPA) oxidation into small non-toxic organics and CO2, and generated CO2 coupled with nitrate-containing wastewater conversion to urea and ammonia on a porous cathode (Zr-Fe/CN). The synergistic effect between anodic BPA oxidation with cathodic CO2 and NO3-reduction improves the electron utilization efficiency and thus increasing the BPA degradation, urea yield rate (UYR) and NH3 yield rate (NYR) by 13.4 % 18.4 % and 8.3 %, respectively. Furthermore, the flow-through operation mode significantly increased the mass transfer efficiency and quickly carried generated CO2 from the anode into the cathode to improve CO2 utilization efficiency. Compared to the parallel plate electrode reactor, the BPA degradation efficiency, UYR and NYR in the flow-through reactor increased from 59.46 % to 84.49 % (the initial concentration of BPA was 40 mg/L), 9.94 mmol h-1g-1 to 19.55 mmol h-1g-1, and 80.31 mmol h-1g-1 to 106.06 mmol h-1g-1 within 60 min, respectively. Moreover, the total carbon conversion efficiency (from BPA to urea) increased from 20.2 % to 42.4 % and the total Faraday efficiency (FE) increased from 78.6 % to 96.3 %. This work provides a multi-win strategy of harmless, resource-based and carbon emission reduction for wastewater treatment.

Recent Progress in Modular Electrochemical Synthesis of Hydrogen and High-Value-added Chemicals based on Solid Redox Mediator

Electrochemical synthesis of H2 and high-value-added chemicals is an efficient and cost-effective approach that can be powered using renewable electricity. Compared to a conventional electrochemical production system, the modular electrochemical production system (MEPS) based on a solid redox mediator (SRM) can separate the anodic and cathodic reactions in time and space. The MEPS can avoid the use of membranes and formation of useless products, as well as eliminate the mutual dependence of production rates at anode and cathode. The SRM can temporarily store or release electrons and ions to pair with cathodic and anodic reactions, respectively, in MEPS. Designing of SRMs with large charge capacity and good cyclability is of great significance for constructing a high-performance MEPS. This work summarizes the design principles, recent advances in MEPS based on SRM, and application in redox flow cells. Moreover, structure design strategies as well as in situ characterization techniques and theoretical calculations for SRM is also proposed. It is expected to promote the vigorous development of MEPS based on SRM. Finally, the challenges and perspectives of MEPS based on SRM are discussed.

Multiscale CO2 Electrocatalysis to C2+ Products: Reaction Mechanisms, Catalyst Design, and Device Fabrication

Electrosynthesis of value-added chemicals, directly from CO2, could foster achievement of carbon neutral through an alternative electrical approach to the energy-intensive thermochemical industry for carbon utilization. Progress in this area, based on electrogeneration of multicarbon products through CO2 electroreduction, however, lags far behind that for C1 products. Reaction routes are complicated and kinetics are slow with scale up to the high levels required for commercialization, posing significant problems. In this review, we identify and summarize state-of-art progress in multicarbon synthesis with a multiscale perspective and discuss current hurdles to be resolved for multicarbon generation from CO2 reduction including atomistic mechanisms, nanoscale electrocatalysts, microscale electrodes, and macroscale electrolyzers with guidelines for future research. The review ends with a cross-scale perspective that links discrepancies between different approaches with extensions to performance and stability issues that arise from extensions to an industrial environment.

Coupling CO2-to-Ethylene Reduction with the Chlor-Alkaline Process in Seawater through In Situ-Formed Cu Catalysts

The overall commercial value of a CO₂ electroreduction system is hindered by the valueless product and high energy consumption of the oxygen evolution reaction (OER) at the anode. Herein, with an in situ-formed copper catalyst, we employed the alternative chlorine evolution reaction for OER, and high-speed formation of both C2 products and hypochlorite in seawater can be realized. The EDTA in the sea salt electrolyte can trigger an intense dissolution and deposition of Cu on the surface of the electrode, resulting in the in situ formation of dendrites of Cu with high chemical activity. In this system, a faradaic efficiency of 47% can be realized for C₂H₄ production at the cathode and a faradaic efficiency of 85% can be realized for hypochlorite production at the anode with an operation current of 100 mA/cm². This work presents a system for designing a highly efficient coupling system for the CO₂ reduction reaction and alternative anodic reactions toward value-added products in a seawater environment.

Coupling Value-Added Anodic Reactions with Electrocatalytic CO2 Reduction

Electrocatalytic CO₂ reduction features a promising approach to realize carbon neutrality. However, its competitiveness is limited by the sluggish oxygen evolution reaction (OER) at anode, which consumes a large portion of energy. Coupling value-added anodic reactions with CO₂ electroreduction has been emerging as a promising strategy in recent years to enhance the full-cell energy efficiency and produce valuable chemicals at both cathode and anode of the electrolyzer. This review briefly summarizes recent progresses on the electrocatalytic CO₂ reduction, and the economic feasibility of different CO₂ electrolysis systems is discussed. Then a comprehensive summary of recent advances in the coupled electrolysis of CO₂ and potential value-added anodic reactions is provided, with special focus on the specific cell designs. Finally, current challenges and future opportunities for the coupled electrolysis systems are proposed, which are targeted to facilitate progress in this field and push the CO₂ electrolyzers to a more practical level.