Photoelectrocatalytic oxidation of methane over three-dimensional ZnO/CdS/NiFe layered double hydroxide

The direct conversion of methane into methanol and other high value-added chemicals with low-energy consumption has always been an important goal and a major challenge for the sustainable chemical industry. In this paper, a three-dimensional (3D) ZnO/CdS/NiFe layered double hydroxide (LDH) shell/core/hierarchical nanowire arrays (NWAs) structure material was fabricated and utilized for photoelectrocatalytic oxidation of methane at room temperature under simulated sunlight. Results show that the ZnO/CdS/NiFe-LDH photoanode exhibites excellent photoelectrochemical performance and catalytic activity. The photocurrent density under the methane atmosphere reached 6.57 mA·cm⁻² at 0.9 V (vs RHE). Yields of methane oxidation products, which mainly are methanol (CH₃OH) and formic acid (HCOOH), catalyzed by the synthesized ZnO/CdS/NiFe-LDH composite are 5.0 and 6.3 times those of pure ZnO, respectively. The total Faraday efficiency of the two main products reach 54.87%. The deposition of CdS nanoparticles (NPs) significantly facilitates the absorption of visible light and promotes the separation of photo-generated carriers. The introduction of NiFe-LDH nanosheets with a three-dimensional porous structure improves the surface reaction kinetics of methane oxidation, acting as an excellent co-catalyst. It also effectively inhibites the production of O₂^•-, preventing O₂^•- from further oxidizing methanol and formic acid into CO₂, which improves the selectivity of methanol and formic acid. Finally, this paper proposed a mechanism of the photoelectrocatalytic oxidation of methane to methanol and formic acid over 3D ZnO/CdS/NiFe-LDH composite material, which provides a new idea for the conversion of methane into high-value chemicals with low-energy consumption.