Engineering efficient bifunctional catalysts for hydrogen production is crucial for advancing hydrogenation technologies and reducing infrastructure costs. However, the inferior kinetics of water dissociation during the hydrogen evolution reaction (HER) and the sluggish OH⁻ adsorption during oxygen evolution reaction (OER) under alkaline conditions greatly hinder their electrolytic efficiencies. Given this, we established Ni₃S₂-MoS₂ heterojunctions with a tunable built-in electric field (BEF) by integrating nitrogen-doped carbon (NC) to enhance water splitting. Specifically, NC-coupled Ni₃S₂-MoS₂ heterojunctions were synthesized by assembling chitosan, thiourea, and sodium molybdate onto nickel foam, followed by carbonization. The chitosan amount was adjusted to control the NC content, which in turn modulated the BEF of the Ni₃S₂-MoS₂ heterojunctions. Profiting from the strong electronegativity, N element serves as an electron acceptor, and the BEF of Ni₃S₂-MoS₂ is effectively manipulated by NC, facilitating fast electron transfer and targeted modulation of active sites. Consequently, the optimized NC-coupled Ni₃S₂-MoS₂ heterojunction with the robust BEF exhibits competitive overpotentials of 75 and 146 mV at 10 mA·cm⁻² for HER and OER, respectively. Relative to Ni₃S₂-MoS₂, theoretical calculations confirm that the robust BEF of NC-coupled Ni₃S₂-MoS₂ lowers the water dissociation energy by 0.62 eV and increases the OH⁻ adsorption energy by 0.22 eV for HER and OER, respectively. Moreover, the robust BEF of NC-coupled Ni₃S₂-MoS₂ contributes to reconstructing a highly active NiOOH phase. This pioneering study introduces a groundbreaking BEF architecture to effectively modulate the surface/interface charge states of electrocatalysts, opening new avenues for exploring robust homologous heterostructures in the future.

Surface-enhanced Raman Spectroscopy (SERS) is a nondestructive technique for rapid detection of analytes even at the single-molecule level. However, highly sensitive and reliable SERS substrates are mostly fabricated with complex nanofabrication techniques, greatly restricting their practical applications. A convenient electrochemical method for transforming the surface of commercial gold wires/foils into silver-alloyed nanostructures is demonstrated in this report. Au substrates are treated with repetitive anodic and cathodic bias in an electrolyte of thiourea, in a one-pot one-step manner. X-rays absorption fine structure (XAFS) spectroscopy confirms that the AuAg alloy is induced at the surface. The unique AuAg alloyed surface nanostructures are particularly advantageous when served as SERS substrates, enabling a remarkably sensitive detection of Rhodamine B (a detection limit of 10⁻¹⁴ ​M, and uniform strong response throughout the substrates at 10⁻¹² ​M).