Insights into the Reaction Energetics and Phase Stability of Electrocatalysts for Upgrading Sustainable Alcohols

The energy efficiency of ambient electrolyzers is currently impacted by oxygen evolution reaction (OER) which not only consumes a significant amount of energy, but also produces oxygen, an intrinsically low value product. When paired with a desired cathodic reaction, such as CO 2 conversion to value-added hydrocarbons, it is imperative to choose an anodic reaction that can utilize the energy supplied to the electrolyzer efficiently. Biomass alcohol oxidation has the potential to not only decrease the overall electrolyzer energy input by >50%, but also address critical needs for biomass conversion, another important 21 st century non-fossil carbon resource. Here, we present the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) as an alternative to OER, as this pathway not only decreases the theoretical overall energy input into the electrolyzer, but also produces FDCA, an important biomass-derived chemical building block for the sustainable polyester PEF, a compelling alternative to fossil-based PET which has a global market size of >30 Mt/yr. In this work, we show a synergistic experimental and computational catalysis framework to gain mechanistic insights into the reaction energetics of HMF oxidation on Ni-based catalysts. We experimentally evaluate the redox features of Ni on supports such as Au in a pH range of 10-13 as a function of Ni film thickness (<1-5 nm) to understand the intrinsic kinetics of HMF oxidation and the support effects on the reaction. Computationally, we compare the reaction energetics of OER and hydride transfer reaction of the HMF oxidation to understand the competing pathways on the anode and perform a bulk Pourbaix analysis as a function of strain caused by the presence of the support lattice to understand the phase stability of Ni oxides under oxidizing conditions. This systematic analysis could potentially serve as new guiding principles to design more energy efficient anodes to upgrade sustainable alcohols. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.