Electroreduction of carbon dioxide to formate at high current densities using tin and tin oxide gas diffusion electrodes

Abstract We investigate tin (Sn) and tin oxide (SnO2) nanoparticle catalysts deposited on gas diffusion layers for the electrochemical reduction of carbon dioxide (CO2) to formate. The performance and durability of these electrodes was evaluated in a gas-fed electrolysis cell with a flowing liquid electrolyte stream and an integrated reference electrode. The SnO2 electrodes achieved peak current densities of 385 ± 19 mA cm−2 while the Sn electrodes achieved peak current densities of 214 ± 6 mA cm−2, both at a formate selectivity > 70%. The associated peak formate production rates of 7.4 ± 0.6 mmol m−2 s−1 (Sn) and 14.9 ± 0.8 mmol m−2 s−1 (SnO2) were demonstrated for a 1-h electrolysis and compare favorably to prior literature. Post-test analyses reveal chemical and physical changes to both cathodes during electrolysis including oxide reduction at applied potentials more negative than − 0.6 V versus RHE, nanoparticle aggregation, and catalyst layer erosion. Understanding and mitigating these decay processes is key to extending electrode lifetime without sacrificing formate generation rates or process efficiency. Graphic abstrac

Enhancing the stability and performance of a battery cathode using a non-aqueous electrolyte

For conductive polymers to be considered materials for energy storage, both their electroactivity and stability must be optimized. In this study, a non-aqueous electrolyte (0.2 M LiClO(4) in acetonitrile) was studied for its effect on the charge storage capacity and stability of two materials used in batteries developed in our laboratory, polypyrrole (pPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) doped with 2,2'-azino-bis(3-ethylbenzothiaxoline-6-sulfonic acid (ABTS). The results are compared to the performance of these materials in an aqueous electrolyte (0.2 M HCl/aq). Loss of ABTS dopant was eliminated principally due to the low solubility of ABTS in acetonitrile, resulting in cathode materials with improved stability in terms of load cycling and performance.close

Investigation of Pulse-Reverse Electrodeposited Copper Electrocatalysts for Carbon Dioxide Reduction to Ethylene

© The Electrochemical Society. This paper discusses the electrodeposition of thin copper (Cu) films on stainless steel substrates using pulse-reverse waveforms and the suitability of such films for electrocatalytic conversion of carbon dioxide (CO2to hydrocarbon products such as methane and ethylene. Activation of these Cu layers through thermal oxidation and subsequent electrochemical reduction is also explored as a means of tuning selectivity toward higher hydrocarbons. An appreciable benefit in terms of overall hydrocarbon selectivity versus hydrogen evolution and other undesirable side reactions was observed from the use of pulsed methods, and the use of thermal activation resulted in a strong shift in the hydrocarbon product distribution from methane to ethylene

Electrochemical Reduction of CO₂ at Copper Nanofoams

We report the electrochemical reduction of CO₂ at copper foams with hierarchical porosity. We show that both the distribution of products formed from this reaction and their faradaic efficiencies differ significantly from those obtained at smooth electropolished copper electrodes. We attribute these differences to be due to high surface roughness, hierarchical porosity, and confinement of reactive species. We provide preliminary evidence in support of these claims

Nickel Hydroxide Nanofluid Cathodes with High Solid Loadings and Low Viscosity for Energy Storage Applications

Nanofluid electrodes with high loading of active solid materials have significant potential as high energy density flow battery electrolytes; however, two key criteria need to be met: they must have a manageable viscosity for pumping and simultaneously exhibit good electrochemical activity. A typical dispersion of nickel hydroxide nanoparticles (~100 nm) is limited to 5–10 wt.% of solids, above which it has a paste-like consistency, incompatible with flow applications. We report on the successful formulation of stable dispersions of a nano-scale nickel hydroxide cathode (β-Ni(OH)2) with up to 60 wt.% of solids and low viscosity (32 cP at 25 °C), utilizing a surface graft of small organic molecules. The fraction of grafting moiety is less than 3 wt.% of the nanoparticle weight, and its presence is crucial for the colloidal stability and low viscosity of suspensions. Electrochemical testing of the pristine and modified β-Ni(OH)2 nanoparticles in the form of solid casted electrodes were found to be comparable with the latter exhibiting a maximum discharge capacity of ~237 mAh/g over 50 consecutive charge–discharge cycles, close to the theoretical capacity of 289 mAh/g

Surface Modification Approach to TiO₂ Nanofluids with High Particle Concentration, Low Viscosity, and Electrochemical Activity

This study presents a new approach to the formulation of functional nanofluids with high solid loading and low viscosity while retaining the surface activity of nanoparticles, in particular, their electrochemical response. The proposed methodology can be applied to a variety of functional nanomaterials and enables exploration of nanofluids as a medium for industrial applications beyond heat transfer fluids, taking advantage of both liquid behavior and functionality of dispersed nanoparticles. The highest particle concentration achievable with pristine 25 nm titania (TiO₂) nanoparticles in aqueous electrolytes (pH 11) is 20 wt %, which is limited by particle aggregation and high viscosity. We have developed a scalable one-step surface modification procedure for functionalizing those TiO₂ nanoparticles with a monolayer coverage of propyl sulfonate groups, which provides steric and charge-based separation of particles in suspension. Stable nanofluids with TiO₂ loadings up to 50 wt % and low viscosity are successfully prepared from surface-modified TiO₂ nanoparticles in the same electrolytes. Viscosity and thermal conductivity of the resulting nanofluids are evaluated and compared to nanofluids prepared from pristine nanoparticles. Furthermore, it is demonstrated that the surface-modified titania nanoparticles retain more than 78% of their electrochemical response as compared to that of the pristine material. Potential applications of the proposed nanofluids include, but are not limited to, electrochemical energy storage and catalysis, including photo- and electrocatalysis

<i>In Situ</i> Measurement of Voltage-Induced Stress in Conducting Polymers with Redox-Active Dopants

Minimization of stress-induced mechanical rupture and delamination of conducting polymer (CP) films is desirable to prevent failure of devices based on these materials. Thus, precise <i>in situ</i> measurement of voltage-induced stress within these films should provide insight into the cause of these failure mechanisms. The evolution of stress in films of polypyrrole (pPy), doped with indigo carmine (IC), was measured in different electrochemical environments using the multibeam optical stress sensor (MOSS) technique. The stress in these films gradually increases to a constant value during voltage cycling, revealing an initial break-in period for CP films. The nature of the ions involved in charge compensation of pPy­[IC] during voltage cycling was determined from electrochemical quartz crystal microbalance (EQCM) data. The magnitude of the voltage-induced stress within pPy­[IC] at neutral pH correlated with the radius of the hydrated mobile ion in the order Li⁺ > Na⁺ > K⁺. At acidic pH, the IC dopant in pPy­[IC] undergoes reversible oxidation and reduction within the range of potentials investigated, providing a secondary contribution to the observed voltage-induced stress. We report on the novel stress response of these polymers due to the presence of pH-dependent redox-active dopants and how it can affect material performance