Defect Engineed 2D Layered Double Hydroxide Electrocatalysts for Improved Water and Biomass Electro-Oxidation

Layered double hydroxides (LDHs) are promising materials due to their ability to modulate metal chemistries within 2D lattice that allows an optimized structure and electronics for the limiting oxygen evolution reaction (OER) and alternative biomass electro-oxidation. Substantial efforts have been devoted in developing transition metal (double) hydroxide based electrocatalysts for oxygen evolution reaction (OER) in alkaline electrolyte. Still, the fundamental understanding of electrocatalytic structure and its influence on reactivity is limited, particularly in electrochemical biomass conversion reactions. The most common LDHs for electrochemical conversions employ a base structure of M²⁺/M³⁺hydroxides using Co, Fe, and/or Ni, where reaction performance can be improved with the inclusion of high valency metal dopants, modulation of the interlayer spacing/anion chemistry and heterostructuring onto various substrates (e.g., graphene, carbon nanotubes). Though relatively understudied, the incorporation of oxygen vacancies (V_O) have also shown the ability to greatly improve the electrochemical performance. From a fundamental prospective, the precise role of V_O is not well elucidated, leading to lack of atomic-scale insights needed for further electrocatalyst development for OER and biomass electro-oxidation. Here we report, an alternative approach to elucidate electrocatalytic structure and activity relationships in Cerium and lanthanum doped transition metal (such as Co, Ni, Fe) based layered (double) hydroxide electrocatalyts. High resolution TEM, EDX mapping and AFM revealed layered structure with uniform incorporation of Cerium/Lanthanum in layered structure. High Energy XRD derived pair distribution function (PDF) analysis described the long range crystalline nature of as synthesized LDH materials. The electrochemical performance tests revealed Cerium/Lanthanum doping is not only beneficial for OER but also synergetic to biomass conversion. The atomic level structural insights through in-situ X-ray absorption spectroscopy allows density functional theory (DFT) to predict synergetic role of Cerium. These atomic level structural atrributes correlated with electrocatalyst activity are essential for rationally design low cost, able to generate high current density with low overpotential and long term stable electrocatalysts to meet practical requirements. Taken together, our work not only demonstrates the ease of V_O generation through Ce doping but provides further atomic scale insights needed to guide future LDH development for OER and other potential electrooxidation reactions.