Black-silicon (b-Si) nanowire photocathodes provide excellent light trapping; however, their high-area interfaces frequently

accelerate charge recombination and photocorrosion during photoelectrochemical (PEC) hydrogen evolution in 

strong acid. We present a multifunctional thermal TiN-centered interfacial engineering approach for fabricating p-Si (100)-

based nanowire photocathodes, enhancing the PEC water-splitting efficiency for solar hydrogen production. TiN was 

selected as the interfacial layer because it combines electrical conductivity, conformal ALD growth, chemical robustness, 

and protective passivation, thereby addressing the limitations of insulating oxide-based protection layers. An ultrathin TiN 

layer deposited by thermal atomic layer deposition (ALD) acts as a conductive passivation/protection structure, facilitating 

the durable incorporation of a solution-processed MoSx co-catalyst (derived from (NH4)2MoS4) and sparsely distributed Pt 

nanoparticles. A systematic TiN thickness series (3 to15 nm) identifies 5 nm as an optimal window, increasing the photocurrent

at 0 V vs. RHE from −0.143 mA cm−2

 for bare b-Si to -0.288 mA cm−2

 after TiN passivation. Following MoSₓ 

functionalization and the electrodeposition of a small amount of Pt, the optimized photocathode achieves a photocurrent 

density of -3.7 mA cm−2

 at 0 V vs. RHE and shows significantly improved photocurrent retention over 6 h of operation 

in a harsh acidic electrolyte. This study reveals that the conformal 5 nm TiN interlayer acts as a critical multifunctional 

platform, simultaneously providing efficient charge extraction, effective surface passivation, and robust chemical protection

against acid corrosion. This nanoscale interface engineering strategy effectively separates surface passivation from 

catalytic activity, overcoming the conventional trade-off between optical transparency and long-term chemical durability 

in silicon-based PEC photocathodes.