The electrochemical conversion of 5-Hydroxymethylfurfural, especially its reduction, is an attractive green production pathway for carbonaceous e-chemicals. We demonstrate the reduction of 5-Hydroxymethylfurfural to 5-Methylfurfurylalcohol under strongly alkaline reaction environments over oxide-derived Cu bimetallic electrocatalysts. We investigate whether and how the surface catalysis of the MOx phases tune the catalytic selectivity of oxide-derived Cu with respect to the 2-electron hydrogenation to 2.5-Bishydroxymethylfuran and the (2 + 2)-electron hydrogenation/hydrogenolysis to 5-Methylfurfurylalcohol. We provide evidence for a kinetic competition between the evolution of H2 and the 2-electron hydrogenolysis of 2.5-Bishydroxymethylfuran to 5-Methylfurfurylalcohol and discuss its mechanistic implications. Finally, we demonstrate that the ability to conduct 5-Hydroxymethylfurfural reduction to 5-Methylfurfurylalcohol in alkaline conditions over oxide-derived Cu/MOx Cu foam electrodes enable an efficiently operating alkaline exchange membranes electrolyzer, in which the cathodic 5-Hydroxymethylfurfural valorization is coupled to either alkaline oxygen evolution anode or to oxidative 5-Hydroxymethylfurfural valorization.

Anion exchange membrane water electrolysis (AEMWE) is an attractive emerging green hydrogen technology. However, the scaling of trends in activity of anode catalysts for the oxygen evolution reaction (OER) from a liquid-electrolyte, three-electrode environment to the two-electrode single-cell format has remained poorly considered. Herein, we critically investigate the scaling of kinetic and catalytic properties of a family of highly active Ni foam (NF) supported, anion (A–)-tuned NiFe(-A–)-OER catalysts. Trends in catalytic activity suggest impressive improvements of up to 91-fold in three-electrode setups (3LC) compared to uncoated NF. While we demonstrate the successful qualitative structure–performance tunability in a 5 cm2 AEMWE single cell, we also find serious limitations in the quantitative predictability of three-electrode setups for single-cell performance trends. Cell environments appear to equalize the cell performances of designer catalysts, which has important ramifications for electrode development. We succeed in analyzing and discussing some of these translation limitations in terms of previously overlooked effects summarized in the activity improvement factor f.

Determination of the electrochemically active surface area (ECSA) is essential in electrocatalysis to provide surface normalized intrinsic catalytic activity. Conventionally, ECSAs of metal oxides and hydroxides are estimated using double layer capacitance (Cdl) measured at nonfaradaic potential windows. However, in the case of Ni-based hydroxide catalysts for the oxygen evolution reaction (OER), the nonfaradaic potential region before the Ni(II) oxidation peak is nonconductive, which hinders accurate electrochemical measurements. To overcome this problem, in this work, we have investigated the use of electrochemical impedance spectroscopy (EIS) at reactive OER potentials to extract the capacitance that is hypothesized to arise due to reactive OER intermediates (O*, OH*, OOH*) adsorbed on the catalyst surface. This allowed the estimation of ECSA and intrinsic activity of NiFe layered double hydroxide (NiFe LDH), the most active, state-of-the-art OER electrocatalyst in alkaline media. We analyzed the OER adsorbates capacitance (Ca) on NiFe LDH and Ni(OH)2 at different electrode potentials and identified a suitable potential range for accurate ECSA evaluation. Finally, we validated our method and the choice of potential range through rigorous catalyst loading and support studies.

Layered double hydroxides (LDHs) are promising catalysts for the oxygen evolution reaction (OER) given their modular chemistry and ease of synthesis. Herein, we report a facile strategy for inclusion of oxygen vacancies (VO) using Ce as a promoter in Co–Ni LDHs that significantly enhances the activity for OER. In situ X-ray absorption spectroscopy (XAS) uncovers an increase in octahedral Co sites and VO upon addition of Ce that promotes the transformation of the LDH into an oxyhydroxide-reactive phase more readily. The presence of an OER-active oxyhydroxide phase along with the generation of VO facilitated by the partial reduction of Ce4+ to Ce3+ under oxidizing conditions results in a better electrochemical activity of Ce-doped electrocatalysts. Density functional theory calculations further corroborate the in situ XAS experimental findings by showcasing that the presence of both Ce and VO reduces the free-energy barrier of the rate-limiting OH* deprotonation step during OER. This work showcases how an enhanced understanding of the role of VO promoters in LDH electrocatalysts can provide insights for future catalyst design in anodic reactions.