On the performance of a polymer electrolyte membrane electrochemical reactor for electrosynthesis of carboxylic acids in alkaline media

A novel polymer electrolyte membrane electrochemical reactor (PEMER) configuration has been employed for the direct electrooxidation of propargyl alcohol (PGA), a model primary alcohol, towards its carboxylic acid derivatives in alkaline medium. The PEMER configuration comprised of an anode and cathode based on nanoparticulate Ni and Pt electrocatalysts, respectively, supported on carbonaceous substrates. The electrooxidation of PGA was performed in 1.0 M NaOH, where a cathode based on a gas diffusion electrode was manufactured for the reduction of oxygen in alkaline conditions. The performance of a novel alkaline anion-exchange membrane based on Chitosan (CS) and Poly(vinyl) alcohol (PVA) in a 50:50 composition ratio doped with a 5 wt.% of poly (4-vinylpyridine) organic ionomer cross-linked, methyl chloride quaternary salt resin (4VP) was assessed as solid polymer electrolyte. The influence of 4VP anionic ionomer loading of 7, 12 and 20 wt.% incorporated into the electrocatalytic layers was examined by SEM and cyclic voltammetry (CV) upon the optimisation of the electroactive area, the mechanical stability and cohesion of the catalytic ink onto the carbonaceous substrate for both electrodes. The performance of the 4VP/CS:PVA membrane was compared with the commercial alkaline anion-exchange membrane FAA -a membrane generally used in direct alcohol alkaline fuel cells- in terms of polarisation plots in alkaline conditions. Furthermore, preparative electrolyses of the electrooxidation of PGA was performed under alkaline conditions of 1 M NaOH at constant current density of 20 mA cm-2 using a PEMER configuration to provide proof of the principle of the feasibility of the electrooxidation of other alcohols in alkaline media. PGA conversion to Z isomers of 3-(2-propynoxy)-2-propenoic acid (Z-PPA) was circa 0.77, with average current efficiency of 0.32. Alkaline stability of the membranes within the PEMER configuration was finally evaluated after the electrooxidation of PGA.This work has been funded by the Spanish MINECO through grants CTQ2013-48280-C3-3-R, at the University of Alicante, and CTQ2012-31229 and RYC2011-08550, at the University of Cantabria. L.G.C. for her PhD fellowship BES-2011-045147 at the University of Alicante and the EEBB-14-09094 mobility grant for a research stay at the University of Cantabria. The authors gratefully thank Dr. José Solla Gullón for his advice on the synthesis of platinum nanoparticles, from the Institute of Electrochemistry at the University of Alicante

Gas-liquid-solid reaction system for CO2 electroreduction to formate without using supporting electrolyte

The use of bismuth-based catalysts is promising for formate production by the electroreduction of CO2 captured from waste streams. However, compared to the extensive research on catalysts, only a few studies have focused on electrochemical reactor performance. Hence, this work studied a continuous-mode gas-liquid-solid reaction system for investigating CO2 electroreduction to formate using Bi-catalyst-coated membrane electrodes as cathodes. The experimental setup was designed to analyze products obtained in both liquid and gas phases. The influence of relevant variables (e.g., temperature and input water flow) was analyzed, with the thickness of the liquid film formed over the cathode surface being a key parameter affecting system performance. Promising results, including a high formate concentration of 34 g/L with faradaic efficiency for formate of 72%, were achieved.Ministerio de Economía y Competitividad (MINECO) through the projects, Grant/Award Numbers: CTQ2016‐76231‐C2‐1‐R, CTQ2016‐76231‐C2‐2‐R (AEI/FEDER, UE).; Vicerrectorado de Investigación y Transferencia de Conocimiento (VITC) of the; University of Alicante, Grant/Award Number: (UTALENTO16‐02)

Continuous carbon dioxide electroreduction to formate coupled with the single-pass glycerol oxidation to high value-added products

CO2 electroreduction has been considered a promising alternative to simultaneously reduce CO2 emissions and produce value-added products. Among others, the production of formic acid/formate is particularly attractive. Although promising results have already been obtained in the literature, one of the recent approaches to improve the process deals with the use of an alternative reaction at the anode instead of the traditional oxygen evolution reaction (OER). In this context, this work reports, for the first time, the study of the CO2 electroreduction to formate coupled with the electrooxidation of glycerol to high-added value products where both half-reactions operate in a continuous mode with a single pass of the reactants through the electrochemical cell. Interestingly, at the cathode, similar results to those previously reported were obtained, reaching formate concentrations of about 18 g·L-1 at a 200 mA·cm-2. In addition, at the anode, promising dihydroxyacetone productions of 196 µmol·m-2·s-1 were simultaneously achieved in the output stream of the anodic compartment. These findings represent a significant step forward for the development and application of the technology.The authors gratefully acknowledge financial support through projects PID2019–108136RB-C31, PID2019–108136RB-C32 and PID2020–112845RB-I00 (AEI/10.13039/501100011033)

PH effects on molecular hydrogen storage in porous organic cages deposited onto platinum electrodes

Hydrogen absorption is a crucial process in energy storage (microscopic or macroscopic) and management and here a porous organic cage (POC) material is shown to bind and release hydrogen when deposited directly onto a platinum electrode and immersed into aqueous electrolyte. Preliminary voltammetry experiments for the POC CC3 deposited onto a platinum disc electrode reveal uptake and release of hydrogen gas (probably coupled to water release and uptake, respectively) in the vicinity of the electrode. Significant pH effects on the rate of binding and release are reported and explained with a change in H2 binding rate. In future, “wet” POCs or POCs dispersed in aqueous solution could be employed for enhancing hydrogen capture/transport in energy applications.N.H. and J.I. thank MINICINN, Spain (projects CTQ2013-48280-C3-3-R and CTQ2016-76231-C2-2-R (AEI/FEDER, UE)) for financial support and the University of Alicante for support for a PhD exchange visit. J.-S.M.L., M.E.B., and A.I.C. thank EPSRC (EP/H000925/1) for financial support

PH effects on molecular hydrogen storage in porous organic cages deposited onto platinum electrodes

Hydrogen absorption is a crucial process in energy storage (microscopic or macroscopic) and management and here a porous organic cage (POC) material is shown to bind and release hydrogen when deposited directly onto a platinum electrode and immersed into aqueous electrolyte. Preliminary voltammetry experiments for the POC CC3 deposited onto a platinum disc electrode reveal uptake and release of hydrogen gas (probably coupled to water release and uptake, respectively) in the vicinity of the electrode. Significant pH effects on the rate of binding and release are reported and explained with a change in H2 binding rate. In future, "wet" POCs or POCs dispersed in aqueous solution could be employed for enhancing hydrogen capture/transport in energy applications.</p

Improving trade-offs in the figures of merit of gas-phase single-pass continuous CO2 electrocatalytic reduction to formate

The electrochemical conversion of CO2 is gaining increasing attention because it could be considered as an appealing strategy for making value-added products at mild conditions from CO2 captured. In this work, we report a process for the electrocatalytic reduction of CO2 to formate (HCOO-) operating in a continuous way, employing a single pass of the reactants through the electrochemical reactor and using Bi carbon supported nanoparticles in the form of a membrane electrode assembly composed by a Gas Diffusion Electrode, a current collector and a cationic exchange membrane. This contribution presents the best trade-off between HCOO- concentration, Faradaic Efficiency and energy consumption in the literature. We also show noteworthy values of energy consumption required of only 180 kWh·kmol-1 of HCOO-, lower than previous approaches, working at current densities that allow achieving formate concentration higher than 300 g·L-1 and simultaneously, a Faradaic Efficiency close to 90%. The results here displayed make the electrochemical approach closer for future implementation at the industrial scale.The authors of this work would like to acknowledge to the financial support from the MINECO, through the projects CTQ2016-76231-C2-1-R and CTQ2016-76231-C2-2-R (AEI/FEDER, UE). J.S.G acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UTALENTO16-02). G.D.S, M.A.G and A.I filed a patent application on the experimental reaction system discussed here

CO2 electroreduction to formate: continuous single-pass operation in a filter-press reactor at high current densities using Bi gas diffusion electrodes

Electrocatalytic reduction of CO2 has been taken into consideration as a fascinating option to store energy from intermittent renewable sources in the form of chemical value-added products. Among the different value-added products, formic acid or formate is particularly attractive since it can be used as a fuel for low-temperature fuel-cells and as a renewable hydrogen carrier. Very recently, a rapidly increasing number of studies have revealed Bi as a promising electrocatalytic material for the CO2 electroreduction to formate, but the performance of Bi electrodes operating in a continuous mode and high current density (j) has been hardly investigated yet. Thus, this work aims at studying the CO2 electroreduction to formate working in a continuous mode in a filter-press-reactor at a j up to 300 mA·cm-2 using Bi electrodes. Bismuth Gas Diffusion Electrodes (Bi-GDEs) were fabricated from carbon-supported Bismuth-nanoparticles. The influence of j and the electrolyte flow/area ratio in the performance of the Bi-GDEs towards formate were evaluated. Working at j of 300 mA·cm-2, a concentration of 5.2 g formate·L-1 with a faradaic efficiency (FE) and rate of 70% and 11mmol·m-2·s-1, respectively were achieved. Lowering the j to 90 mA·cm-2, formate concentrations of up to 7.5 g·L-1 could be obtained with an excellent FE of 90%. Interestingly, the highest concentration of formate obtained was 18 g·L-1, but at expenses of an important decrease in FE. Although the results of this study are interesting and promising, further research is required to increase formate concentration for a future implementation at industrial scale.The authors of this work would like to show their gratitude to the financial support from the MINECO, through the projects CTQ2016-76231-C2-1-R and CTQ2016-76231-C2-2-R (AEI/FEDER, UE). Jose Solla-Gullón also acknowledges the financial support from VITC of the University of Alicante (UTALENTO16-02)

Carbonization of polymers of intrinsic microporosity to microporous heterocarbon:Capacitive pH measurements

A nitrogen-containing polymer of intrinsic microporosity (PIM-EA-TB-H2; nitrogen adsorption surface area 846 m2 g−1) is vacuum carbonized at 700 °C and thereby directly without post-treatment converted into a microporous heterocarbon (cPIM; N2 adsorption surface area 425 m2 g−1). Nitrogen functionalities in the polymer backbone are retained in the heterocarbon and appear responsible for unusual time-, electrolyte-, and pH-dependent properties. Electrochemical characterization suggests a high specific capacitance (typically 50 F g−1) but only after prolonged immersion in aqueous HClO4. The time-dependent increase in capacitance during immersion is assigned to slow hydration and ingress of HClO4 into hydrophobic micropores (H2SO4 or H3PO4 are more hydrophilic and much less effective). Once hydrated, the microporous heterocarbon exhibits pH-dependent capacitance “switching” over a wide pH range and analytical applications as “capacitive” pH sensor are proposed.</p

Coupling glycerol oxidation reaction using Ni-Co foam anodes to CO2 electroreduction in gas-phase for continuous co-valorization

Electrocatalytic reduction of CO2 is a promising alternative for storing energy and producing valuable products, such as formic acid/formate. Continuous gas-phase CO2 electroreduction has shown great potential in producing high concentrations of formic acid or formate at the cathode while allowing the oxygen evolution or the hydrogen oxidation reactions to occur at the anode. It is advantageous to use a more relevant oxidation reaction, such as glycerol which is a plentiful by-product of current biodiesel production process. This work successfully manages to couple the glycerol oxidation reaction with continuous gas-phase CO2 electroreduction to formate with the implementation of Ni-Co foam-based anodes. The MEA-electrolyzer developed can achieve significantly high formate concentrations of up to 359 g L-1 with high Faradaic efficiencies of up to 95%, while also producing dihydroxyacetone at a rate of 0.434 mmol m−2 s−1. In comparison with existing literature, this represents an excellent trade-off between relevant figures of merit and can remarkably contribute to a future implementation of this coupled electrochemical system approach at larger scales.The authors gratefully acknowledge financial support through projects PID2019-108136RB-C31, PID2019-108136RB-C32 and PID2019-108136RB-C33, PID2020-112845RB-I00, TED2021–129810B-C21 and PLEC2022-009398 (MCIN/AEI/10.13039/501100011033 and Unión Europea Next GenerationEU/PRTR). This project has received funding from the European Union’s Horizon Europe research and innovation programme under grant agreement No 101118265​