An efficient visible light-driven double-well-based Pt/CdS/3D-graphene heterostructure for electrocatalytic and photo-electrocatalytic methanol oxidation†

In this article, the impact of the loading of CdS between Pt and 3D graphene was investigated determining enhanced visible light absorption and efficient charge separation at the interfaces that have improved methanol oxidation reaction activities. The structural, morphological, optical and electrochemical properties of photoanodes were investigated. The highest current density reached 264 mA cm⁻² at 0.28 V vs. Ag/AgCl under one sun illumination for Pt/10-CdS/3D-Gr@Ni-Foam as compared to 116 mA cm⁻² at 0.26 V for Ag/AgCl in the dark at a scan rate of 10 mV s⁻¹. The diffusion coefficient of electron transfer is also enhanced to 3.99 × 10⁻³ cm² s⁻¹ under illumination as compared to 2.971 × 10⁻³ cm² s⁻¹ under dark conditions for the Pt/10-CdS/3D-Gr@Ni-Foam heterostructure. The decrease in the charge transfer resistance (R_ct) from 34.31 Ω to 2.38 Ω indicated that the introduction of CdS enhanced the separation and transportation of photoexcited charges and also improved the kinetics of the electron transfer reaction. The Pt/10-CdS/3D-Gr@Ni-Foam exhibited a significantly enhanced net donor density (N_D) of 2.5 × 10²⁰, surpassing the donor density of 1.5 × 10²⁰ of the Pt/3D-Gr@Ni-Foam. Both Pt and 3D-graphene are being utilized as a well, for efficient charge separation and transportation at either side of the CdS sandwich, resulting in effective transfer of charges at the corresponding Pt/CdS/3D-Gr@Ni-Foam heterostructure interfaces and increased electron density on Pt showed its unprecedented potential to be utilized for electrocatalytic and photo-electrocatalytic applications.