Continuously Producing Highly Concentrated and Pure Acetic Acid Aqueous Solution via Direct Electroreduction of CO₂

Abstract

It is crucial to achieve continuous production of highly concentrated and pure C 2 chemicals through the electrochemical CO 2 reduction reaction (eCO 2 RR) for artificial carbon cycling, yet it has remained unattainable until now. Despite one-pot tandem catalysis (dividing the eCO 2 RR to C 2 into two catalytical reactions of CO 2 to CO and CO to C 2 ) offering the potential for significantly enhancing reaction efficiency, its mechanism remains unclear and its performance is unsatisfactory. Herein, we selected different CO 2 -to-CO catalysts and CO-to-acetate catalysts to construct several tandem catalytic systems for the eCO 2 RR to acetic acid. Among them, a tandem catalytic system comprising a covalent organic framework (PcNi-DMTP) and a metal−organic framework (MAF-2) as CO 2 -to-CO and CO-to-acetate catalysts, respectively, exhibited a faradaic efficiency of 51.2% with a current density of 410 mA cm −2 and an ultrahigh acetate yield rate of 2.72 mmol m −2 s −1 under neutral conditions. After electrolysis for 200 h, 1 cm −2 working electrode can continuously produce 20 mM acetic acid aqueous solution with a relative purity of 95+%. Comprehensive studies revealed that the performance of tandem catalysts is influenced not only by the CO supply−demand relationship and electron competition between the two catalytic processes in the one-pot tandem system but also by the performance of the CO-to-C 2 catalyst under diluted CO conditions.

Interparticle Distance Matters for Selectivity Control in Industrially Relevant CO Electrolysis

“…Here we adapt a facile method for the preparation of Cu nanoparticle gas diffusion electrodes (GDEs) with tunable average interparticle distances by physically mixing Cu nanoparticles with carbon black and investigate the effect of the interparticle distance on the product selectivity of CO electrolysis at industrially relevant current densities. Remarkably, increasing the average interparticle distance of Cu nanoparticles in catalyst layers increases the selectivity toward acetate (a specific C 2+ product), which has previously been achieved via manipulating surface structures of Cu catalysts. − ,− Our experimental and numerical calculation results indicate that a larger interparticle distance increases the local pH near Cu nanoparticles and the local CO concentration owing to weakened interparticle CO diffusion at the mesoscale, thus resulting in improved acetate production from CO electrolysis. By further coupling external reaction conditions (i.e., elevated CO pressure and anolyte concentration), the maximum acetate Faradaic efficiency (FE) and acetate partial current density reach 77.5% and 705 mA cm –2 , respectively.…”

“…Efforts for selectivity control in CO 2 /CO electrolysis focus on catalyst structures such as size, shape, composition, defect, oxidation state, and low-coordination sites at the nanoscale and atomic scale. − Meanwhile, factors affecting species transport at the mesoscale such as proximity effect , are of equal importance but often overlooked. The proximity effect has been first reported to tune catalytic activity and selectivity of bifunctional catalysts with two separate active components in thermal catalysis. − The nanoparticle proximity (namely, interparticle distance) effect has recently been revealed in supported metal nanoparticle catalysts for some electrocatalytic reactions, e.g., Pt nanoparticles for oxygen reduction reaction. − Depending on the ratio of interparticle distance and particle size, an overlapping effect in electric double layer , and a shielding or diffusion effect of close nanoparticles ,,, have been proposed for negative and positive effects of larger interparticle distances on catalytic activity and selectivity, respectively.…”

Solid Electrolytes for Low-Temperature Carbon Dioxide Valorization: A Review

“…In addition to the generation of charged liquid products from solid electrolyte-based CO 2 RR, neutral products such as ethanol can also be produced at high concentrations by blocking both convective and diffusive routes . Furthermore, the use of a solid electrolyte layer has been explored in electrocatalytic CO reduction (CORR), enabling the production of pure acetic acid. , CORR has gained significant attention recently due to its numerous advantages compared to the CO 2 RR for the generation of C 2+ chemicals. Furthermore, CO remains stable in alkaline electrolytes, and a higher carbon utilization is expected.…”