Electrochemical Oxidation of Primary Alcohols Using a Co₂NiO₄ Catalyst: Effects of Alcohol Identity and Electrochemical Bias on Product Distribution

Abstract

The electrochemical reduction of CO 2 and H 2 O to solar fuels remains a promising strategy for storing intermittent energy sources in the form of chemical bonds. These electrochemical reductions occurring at the cathode typically are coupled to the oxygen evolution reaction at the anode. The electrochemical oxidation of organic alcohols in the alcohol oxidation reaction is a promising alternative anode reaction that occurs at decreased operating potentials compared to the oxygen evolution reaction and that produces more valuable products than O 2 . Co 2 NiO 4 is a particularly promising catalyst for the oxidation of alcohols, able to promote alcohol oxidation at current densities of 10 mA cm −2 at potentials of only 1.42 V vs reversible hydrogen electrode (RHE) in alkaline aqueous conditions, significantly less positive than typical potentials required for the oxygen evolution reaction. In this work, we study the alcohol oxidation reaction by Co 2 NiO 4 for a series of straight-chain primary alcohols of increasing chain length from ethanol to n-pentanol. We show that the product distribution for alcohol oxidation depends on the alcohol chain length, changing from primarily aldehyde products for shorter-chain alcohols to primarily carboxylic acid products for longer-chain alcohols. These results suggest that alcohols are oxidized sequentially to first aldehydes and then carboxylic acids at Co 2 NiO 4 . During the oxidation of longer-chain alcohols, the aldehyde intermediates are retained at the catalyst surface for longer times, facilitating further oxidation to terminal carboxylic acid products. We also explored the potential-dependent activities and product distributions for nbutanol oxidation at Co 2 NiO 4 , and showed that alcohol oxidation is able to outcompete chloride oxidation in aqueous solutions containing Cl − at seawater concentrations. These studies provide further insight into the alcohol oxidation reaction at Co 2 NiO 4 and highlight its promise as an alternative anode reaction for the production solar fuels.

Microwave-assisted synthesis of ZIF-9@xGO composites as cooperative electrocatalysts for electro-oxidation of benzyl alcohols coupled with H2 production

“…Previous reports have claimed that electrochemical alcohol oxidation proceeds through a cascade catalysis mechanism, where alcohol gets converted to aldehyde via 2e − oxidation, followed by another 2e − oxidation to acid. 40 The benzoic acid selectivity vs. time plot shown in Fig. S14 † was consistent with the abovementioned claim, as at constant potential of 1.50 V vs. RHE, oxidation of BA to benzaldehyde was observed prior to its conversion to benzoic acid.…”

Selective electrosynthesis of platform chemicals from the electrocatalytic reforming of biomass-derived hexanediol

“…No study on the production of 6HA and AA from e-HOR is available currently, but the production of small acids, such as formic acid and acetic acid, from the electrochemical oxidation of alcohols at nickel-based electrocatalysts, has been intensively investigated since the 1970s. 6–15 For instance, the highly selective production of formic acid, in terms of faradaic efficiency of ∼100%, from the electrochemical oxidation of ethylene glycol, has been demonstrated using nickel oxyhydroxide-modified nickel phosphide in our previous work. 6 Therefore, it can be expected that nickel-based electrocatalysts may have electrocatalytic activity towards e-HOR.…”

Ternary Ni–Co–Se Nanostructure for Electrocatalytic Oxidative Value Addition of Biomass Platform Chemicals

“…32 Intrinsic catalytic activity of these hybrid oxyhydroxides could be potentially higher than that of NiOOH. 32 For example, Fe-doped NiOOH is more active than NiOOH for both water oxidation 33 and alcohol oxidation. 34 Inspired by recent advantages in this field, to develop a highperformance catalyst for electrooxidative conversion of biomass-derived chemicals to value-added chemicals, here we present a ternary nickel−cobalt selenide nanostructure for selective conversion of methanol to formate, ethanol to acetic acid, ethylene glycol to formic acid, GlyOH to formic acid, and malic acid to pyruvic acid and oxaloacetic acid.…”

“…Moreover, oxygen vacancy in NiO, , branching in Ni 3 C, facet exposer in Ni nanoparticles, and size of Ni electrocatalyst played a critical role in the methanol/alcohol oxidation reaction. Although NiOOH particularly is more active for water oxidation compared to other 3d metal OOH species (like CoOOH, FeOOH, CuOOH), , doping of secondary 3d metal ions (M) with Ni could be beneficial for the generation of hybrid Ni­(M)­OOH . Intrinsic catalytic activity of these hybrid oxyhydroxides could be potentially higher than that of NiOOH .…”

“…Although NiOOH particularly is more active for water oxidation compared to other 3d metal OOH species (like CoOOH, FeOOH, CuOOH), , doping of secondary 3d metal ions (M) with Ni could be beneficial for the generation of hybrid Ni­(M)­OOH . Intrinsic catalytic activity of these hybrid oxyhydroxides could be potentially higher than that of NiOOH . For example, Fe-doped NiOOH is more active than NiOOH for both water oxidation and alcohol oxidation …”