Solid-Solution Engineering of Earth-Abundant Metal Borides of Y(TM1TM2)B4-Type as Durable High-Current-Density Electrocatalysts for HER

Abstract

Earth-abundant transition-metal borides are promising alternatives to noble-metal catalysts for the hydrogen evolution reaction (HER), but achieving high activity and durability under industrially relevant operating conditions remains challenging. Herein, we develop a series of arc-melted solid-solution transition-metal borides, YCr_1–xMo_xB₄, YCr_1–xW_xB₄, and YMo_1–xW_xB₄ (x = 0.25, 0.5, and 0.75), as robust HER electrocatalysts for acidic media. Through solid-solution engineering, the catalytic performance of the parent borides is significantly improved, with each composition outperforming commercial 20 wt % Pt/C at high current density. Notably, YCr_0.25W_0.75B₄ exhibits the best overall HER performance, requiring only 0.449 V overpotential to reach 1000 mA/cm², compared with 0.742 V for 20 wt % Pt/C. The enhanced activity is further supported by a high double-layer capacitance of 54 mF/cm², reflecting increased electrochemically accessible surface area and abundant exposed HER-active sites. The catalyst also shows excellent acid stability, retaining 92% of its activity after 5000 cycles and 24 h of continuous operation. Scanning electrochemical cell microscopy (SECCM) analysis reveals heterogeneous, composition-dependent local HER behavior, with YMo_0.25W_0.75B₄ exhibiting the least negative onset potential, followed closely by YCr_0.25W_0.75B₄, highlighting the importance of surface composition in controlling catalytic activity. These findings establish solid-solution transition-metal borides as a versatile platform for designing inexpensive, durable, and high current electrocatalysts for sustainable hydrogen production.