Oxygen Vacancy Engineering in Layered Double Hydroxides Modulates Cascade Conversion of Glycerol to Lactic Acid

Abstract

Selective conversion of glycerol to lactic acid having critical economic and environmental value remains a challenge because it requires multiple reaction steps including oxidation, isomerization, and rearrangement, as well as the prevention of C–C cleavage. Herein, we achieved oxygen vacancy engineering in layered double hydroxide (LDH) modified BiVO₄ photoelectrodes to yield a high selectivity for cascade conversion of glycerol to lactic acid in a neutral electrolyte. Operando Raman spectroscopy and in situ Fourier-transform infrared adsorption spectroscopy confirmed the dehydrogenation of the secondary hydroxyls of glycerol and the formation of a key intermediate 1,3-dihydroxyacetone via photoinduced Co²⁺–OH dynamic evolution. Theoretical calculations and time-resolved infrared spectra revealed that the adsorption of 1,3-dihydroxyacetone terminal hydroxyls on Co²⁺–OH sites adjacent to oxygen vacancy defects reduced the energy barrier of the dehydration step, leading to isomerization and hydration rearrangement to lactic acid. This study provides unique insights into the dehydrogenation–isomerization cascade of glycerol on the oxygen vacancies of LDH via a photoelectrochemical pathway, which directs an alternative means of alkali-free glycerol conversion to lactic acid.