Unleashing the Power of P‐N Heterojunctions: Optimizing Water Electrolysis Efficiency Through a Cathode‐Driven Electrocatalyst Synergy

ABSTRACT In water electrolysis, the oxygen evolution reaction (OER) at the anode requires a higher overpotential than the hydrogen evolution reaction (HER) at the cathode; thus, the activity of the anode catalyst is crucial to the overall energy consumption and reaction rate. We demonstrate an exfoliated molybdenum diselenide nanosheet (MoSe ₂ )/polyaniline (PANI) system with a P‐N heterojunction that exhibits excellent HER activity as the cathode catalyst in alkaline conditions, and effectively balances the overall water electrolysis reaction and significantly enhances OER performance and anode stability. Specifically, in a dual‐electrode H‐cell, the Tafel slope of the MoSe ₂ /PANI anode decreased from 115.81 mV/dec to 65.17 mV/dec, and resistance dropped from 2.5 to 0.5 Ω, indicating the MoSe ₂ /PANI cathode significantly enhances the anode's catalytic ability compared to commercial platinum‐based precious metal catalysts. Importantly, this system exhibits an exceptionally low total overpotential of 1.48 V at 10 mA/cm ² , with no significant changes in the total overpotential or Tafel slope after long‐term constant current density and cyclic voltammetry treatments. In contrast, precious metal catalyst systems degraded significantly. This groundbreaking discovery confirms that the P‐N heterojunction in the cathode catalyst is key to optimizing water electrolysis performance and provides valuable insight for future water electrolysis and emerging energy technologies.