Formate Over‐Oxidation Limits Industrialization of Glycerol Oxidation Paired with Carbon Dioxide Reduction to Formate

Abstract

Electrocatalytic CO 2 reduction processes are generally coupled with the oxidation of water. Process economics can greatly improve by replacing the water oxidation with a more valuable oxidation reaction, a process called paired electrolysis. Here we report the feasibility of pairing CO 2 reduction with the oxidation of glycerol on Ni 3 S 2 /NF anodes to produce formate at both anode and cathode. Initially we optimized the oxidation of glycerol to maximize the Faraday efficiency to formate by using design of experiments. In flow cell electrolysis, excellent selectivity (up to 90 % Faraday efficiency) was achieved at high current density (150 mA/cm 2 of geometric surface area). Then we successfully paired the reduction of CO 2 with the oxidation of glycerol. A prerequisite for industrial application is to obtain reaction mixtures with a high concentration of formate to enable efficient downstream separation. We show that the anodic process is limited in formate concentration, as Faraday efficiency to formate greatly decreases when operating at 2.5 M formate (~10 w%) in the reaction mixture due to over-oxidation of formate. We identify this as a major bottleneck for the industrial feasibility of this paired electrolysis process.

Single-Pass Electrooxidation of Glycerol on Bismuth-Modified Platinum Electrodes as an Anodic Process Coupled to the Continuous CO2 Electroreduction toward Formate

“…In this way, coupling more valuable anodic reactions with CO 2 electroreduction has been the subject of recent and valuable contributions − and has emerged as a promising approach to lower the overall cell voltage, and consequently the energy efficiency of the system, and also to simultaneously produce high-added-value products both at the cathode and anode. Among the different anodic processes used as paired reactions with CO 2 RR, the electrooxidation of glycerol (GOR, glycerol oxidation reaction) to high-added-value products is one of the most interesting alternatives. ,,,,− Glycerol is the major waste product from biodiesel production and can be electrochemically oxidized into a variety of valuable chemicals. − In this sense, Verma et al demonstrated that coupling CO 2 RR with the electrooxidation of glycerol reduced the power consumption of the system by 53% compared to use of the OER as anodic process. More recently, Junqueira et al reported the simultaneous production of formate both at the anode and cathode from the paired CO 2 RR and glycerol electrooxidation at high currents (200 mA cm 2 ) with FEs of about 96 and 45% at the anode and cathode, respectively.…”