A porous network of boron-doped IrO nanoneedles with enhanced mass activity for acidic oxygen evolution reactions.

While proton exchange membrane water electrolyzers (PEMWEs) are essential for realizing practical hydrogen production, the trade-off among activity, stability, and cost of state-of-the-art iridium (Ir)-based oxygen evolution reaction (OER) electrocatalysts for PEMWE implementation is still prohibitively challenging. Ir minimization coupled with mass activity improvement of Ir-based catalysts is a promising strategy to address this challenge. Here, we present a discovery demonstrating that boron doping facilitates the one-dimensional (1D) anisotropic growth of IrO crystals, as supported by both experimental and theoretical evidence. The synthesized porous network of ultralong boron-doped iridium oxide (B-IrO) nanoneedles exhibits improved electronic conductivity and reduced charge transfer resistance, thereby increasing the number of active sites. As a result, B-IrO displays an ultrahigh OER mass activity of 3656.3 A g with an Ir loading of 0.08 mg cm, which is 4.02 and 6.18 times higher than those of the un-doped IrO nanoneedle network (L-IrO) and Adams IrO nanoparticles (A-IrO), respectively. Density functional theory (DFT) calculations reveal that the B doping moderately increases the d-band center energy level and significantly lowers the free energy barrier for the conversion of *O to *OOH, thereby improving the intrinsic activity. On the other hand, the stability of B-IrO can be synchronously promoted, primarily attributed to the B-induced strengthening of the Ir bonds, which help resist electrochemical dissolution. More importantly, when the B-IrO catalysts are applied to the membrane electrode assembly for PEM water electrolysis (PEMWE), they generate a remarkable current density of up to 2.8 A cm and maintain operation for at least 160 h at a current density of 1.0 A cm. This work provides new insights into promoting intrinsic activity and stability while minimizing the usage of noble-metal-based OER electrocatalysts for critical energy conversion and storage.