Unveiling charge dynamics of Co3S4 nanowalls/CdS nanospheres n-n heterojunction for efficient photoelectrochemical Cr(VI) detoxification and N2 fixation

Photoelectrochemical (PEC) conversion of solar energy is a sustainable and ecological approach as it offers green energy carriers, renewable fuels as well as environmental remediation. Herein, a polyaniline-coated anodized stainless-steel mesh (PANI-ASSM) was supported n-n heterojunction of CdS nanosphere (NSs)-Co3S4 nanowalls (NWs) by a simple step by step electrochemical deposition method. The PEC performance of the developed photoanode was then assessed toward Cr(VI) detoxification and N2 fixation. The PL, UV-Vis, electrochemical impedance spectroscopy (EIS), intensity-modulated photocurrent spectroscopy (IMPS), cyclic voltammetry (CV), transient photocurrent (TPC), chronopotentiometry, and Bode phase tests also proved the excellent PEC performance and significant stability of this catalyst. UV-vis, Urbach energy (UE), Mott-Schottky (M-S), and linear sweep voltammetry (LSV) results coupled to the Robert Mulliken method confirmed the formation of robust n-n CdS-NSs-Co3S4-NWs heterojunction with viable band edge potential for Cr(VI) detoxification and N2 fixation; while PANI only acted as a powerful bridge to transfer the photo-generated electrons to ASSM support. The possible mechanism was investigated by experimental and electrochemical analysis which suggested a 3-electron-coupled Cr(VI) and 6-electron-coupled N2 reduction pathway. Such a PEC exhibited considerable electrocatalytic performance due to effective electron-hole separation with an ammonia yield and Cr(VI) reduction of 12.33 mu g/mol.h NH3 and 90.61%, respectively. This work presented a new paradigm for the illustrative design of promising photoanodes for renewable fuel production and detoxification performance.

Automated summary

This study presents a polyaniline-coated anodized stainless-steel mesh supported n-n heterojunction of CdS nanosphere-Co3S4 nanowalls photoanode for solar energy conversion. The photoanode demonstrates excellent performance in Cr(VI) detoxification and N2 fixation processes. Experimental and electrochemical analysis reveal a possible mechanism involving 3-electron-coupled Cr(VI) reduction and 6-electron-coupled N2 reduction pathways. The PEC exhibits considerable electrocatalytic performance with high ammonia yield and Cr(VI) reduction efficiency.