Cascaded photonic-electronic junction based plasmonic Mott–S scheme heterojunction photoelectrodes for water splitting and Zn-air battery technology

Photo-assisted electrochemical systems present a sustainable pathway for water splitting and metal–air batteries, yet their performance is hindered by poor visible-light utilization, short carrier lifetimes, and sluggish redox kinetics. This work introduces a novel concept of a plasmon-enhanced Mott–S-scheme heterojunction AgCo-Fe 2 O 3 /g-C 3 N 4 , designed to overcome these limitations through a synergistic integration of photonic and plasmonic mechanisms. Nitrogen-deficient g-C 3 N 4 (g-CN) acts as a light-harvesting scaffold, while coupling with Fe 2 O 3 forms an S-scheme junction enabling directional charge migration and selective carrier separation. AgCo nanoparticles introduce localized surface plasmon resonance, simultaneously serving as electron sinks to suppress recombination and as hot-carrier generators that accelerate catalytic turnover. Collectively, these structural and electronic synergies lead to significantly enhanced activity with reduced overpotentials of 78 mV for HER and 174 mV for OER at 10 mA/cm 2 , and a half-wave potential of 0.855 V vs. RHE for ORR in alkaline media; outperforming commercial Pt/C and IrO 2 references. Durable operation is demonstrated in industrial-level water splitting (500 and 1000 mA/cm 2 for 120 h) and extended Zn-air battery cycling (>100 h). Altogether, these findings highlight a mechanistically guided approach to plasmonic Mott–S-scheme heterojunction design, enabling light-assisted redox catalysis across multiple reaction pathways. The study presents a cascaded plasmonic Mott–S-scheme heterojunction, constructed by integrating AgCo nanoparticles with Fe 2 O 3 /g-CN. This architecture synergistically enhances light absorption, charge separation, and catalytic activity within a unified photoelectrocatalytic framework. Hot electron generation from the plasmonic AgCo domain couples with directional charge transfer across the S-scheme interface, while redox-active sites accelerate catalytic turnover. Collectively, these processes extend spectral utilization, suppress carrier recombination, and improve interfacial kinetics, thereby enabling efficient photo-assisted hydrogen evolution (HER), oxygen evolution (OER), and oxygen reduction (ORR). • AgCo-Fe 2 O 3 /g-CN unites photonic and plasmonic effects for enhanced photoactivity. • g-CN/Fe 2 O 3 forms an S-scheme; Ag LSPR adds hot carriers, limits recombination. • Delivers η 10 of 78 mV (HER), 174 mV (OER); ORR E 1/2 = 0.855 V, beating Pt/C, IrO 2 . • Shows long-term stability of 120h for water splitting and >100h Zn–air cycling.