Electrocatalytic hydrogenation coupling oxidation using water in a highly efficient paired cell enabled by an oxygen defect-rich layered double hydroxide

Abstract

Using water as a hydrogen/oxygen source for electrocatalytic production of high-value chemicals is highly desirable from a sustainability perspective due to the pivotal role of reduction/oxidation reactions in chemical industry. However, competition from water splitting into H₂/O₂ typically limits the electron efficiency and process economy. In this work, an oxygen vacancy-rich NiFe-layered double hydroxide (NiFe-LDH)-derived catalyst was obtained by the reduction of monolayer NiFe-LDH (NiFe-mono) at 400 °C in a 10% H₂/Ar atmosphere. NiFe-400 showed outstanding activity for the electrocatalytic reduction of p-nitrophenol (p-NP) to p-aminophenol (p-AP) in 1 M KOH, delivering a faradaic efficiency (FE) above 99%. Under continuous electrolytic reduction conditions, 97% FE could be maintained even at 100 mM p-NP. In situ XAFS and DFT theoretical calculations revealed that the Fe site is the main active site, and the existence of oxygen defects promotes the interaction between the active site and the intermediate of the p-NP hydrogenation reaction. Furthermore, in order to utilize the oxygen evolved by water splitting, a paired electrolysis cell was developed that allowed the simultaneous reduction of p-NP to p-AP over NiFe-LDH at the cathode and 5-hydroxymethylfurfural (HMF) oxidation to 2,5-furandicarboxylic acid (FDCA) over a monolayered NiCo-LDH catalyst (NiCo-mono) at the anode, with the combined anode and cathode FE being >190%. Results encourage the wider use of defect-rich LDHs in green chemical synthesis with water as a hydrogen/oxygen source.