(476g) Probing the Performance and Mechanism of Nickel Iron Oxyhydroxides for Electrocatalytic Benzyl Alcohol Oxidation in Alkaline Media

Electrochemical oxidation of biomass can convert simple organic substrates, such as methanol and benzyl alcohol, into value-added products in a green and sustainable fashion. While nickel-based electrodes have been studied as electrocatalysts for benzyl alcohol oxidation (BAO), the role of impurities, pH, and ionic strength in performance are less understood by the community. Herein, we report BAO performance with a porous nickel-iron (oxy)hydroxide thin film under multiple electrolyte conditions and pHs with parallel computational studies to probe the mechanism. Prior to catalytic testing, the thin films were cathodically electrodeposited from an ultra-pure nickel nitrate solution. Notably, while no iron was intentionally added, x-ray fluorescence (XRF) post analysis suggests that 7 - 22 % iron incorporates into the reaction system during testing. This Fe incorporation was accompanied by small shifts in the Ni²⁺ to Ni³⁺ oxidation peak potential and can deconvolute, to some extent, the differences observed in BAO performances at pH 13 and pH 14. Notably we observe a strong linear correlation between the BAO onset potential and nickel redox potential, suggesting that the nickel-iron (oxy)hydroxide phase plays an important role in BAO catalysis. Parallel density functional theory computational studies support this conclusion and revealed that the rate-determining step is the adsorption of the deprotonated benzyl alcohol species and that bridge-like oxygens at edge-sites are more preferred.

By taking factors, such as impurities, pH, and ionic strength, into account with characterization and electrochemical testing, we can better understand the active material from the BAO catalytic system. By connecting theory to experiment, we can better probe the active sites and reaction mechanism with an aim of designing new specific enhanced active motifs. This study is a step forward in the understanding of nickel-iron electrodes for BAO, and in larger context, the electrocatalytic transformation of biomass.