Alsac, Elif PinarSmith, Rodney2023-05-012023-05-012022-09-28https://doi.org/10.1021/acscatal.2c03645http://hdl.handle.net/10012/19376This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Catalysis, copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see https://doi.org/10.1021/acscatal.2c03645The improved electrocatalytic property of disordered metal hydroxides relative to that of crystalline layered double hydroxides remains a poorly understood phenomenon. We use a hydrothermally synthesized series of mixed metal hydroxides to study these composition-dependent structural similarities and electrochemical behavior differences. X-ray diffraction, X-ray absorption spectroscopy, and Raman spectroscopy provide complementary perspectives on the structure of the FexNi1–x(OH)2 series. These techniques reveal near quantitative incorporation of Fe(III) into the Ni(OH)2 lattice at low Fe-content but also that Fe(III) is distributed into a contaminating iron oxide phase and a non-traditional coordination environment atop the layered double hydroxide structure as the Fe-content increases. Systematic lattice contraction is observed with increasing Fe-content, similar to structurally disordered analogues, but the electrochemical behavior is markedly different. The characteristic anodic shift of pre-catalytic redox peaks does not occur, and electron transfer kinetics exhibit a much more gradual improvement. Measured Tafel slopes are found to possess a linear relationship with the O–Ni–O bond angles within the lattice across the full composition series. The asymmetric Marcus–Hush theory is used to explain this unexpected result, where Fe(III) ions systematically introduce a lattice strain that alters the reaction coordinate for the nickel oxidation reactions.enhydrothermal synthesislattice strainelectron transfer kineticselectrocatalystsiron-nickel hydroxideMarcus-Hush theoryArticle