Grain Boundary Engineering of Mo₂C via Pulsed Laser for Enhanced Hydrogen Evolution

The production of clean hydrogen using water electrolysis is a crucial element in achieving sustainable energy production and utilization systems. A key challenge in using hydrogen as an energy source is to understand and control the hydrogen evolution reaction (HER) dynamics and develop low-cost and high-performance catalysts suitable. Although noble metal-based (e.g., platinum, iridium, ruthenium) catalysts show good performance in HER, they have limitations due to their high cost and scarcity. As an alternative, transition metal carbides, which are non-novle metals, have been studied extensively due to their good performance, stability, and low cost. Methods such as structural engineering, alloying, and heteroelement doping have been mainly used to improve catalyst performance, but strategies using grain boundaries (GBs), which account for most of the crystal defects in crystals, have not made much progress due to their complexity.<br/>Here, we report pulsed laser-based synthesis method for molybdenum carbide (Mo₂C) with high density of GBs. The method using a laser not only reduces the Mo₂C precursor to a Mo₂C crystal through a photothermal reaction, but can also create crystal defects through fast heating/cooling times.<br/>In particular, we fabricated a Mo₂C film with an ultrahigh GB density of 121.13 μm^-1 (at 20 μs pulse duration) by systematically controlling the heat accumulation effect depending on the pulse duration of the laser and the thermal properties of material.<br/>Consequently, Mo₂C films with high density of GBs not only enhance the activity by tensile/compressive stresses occurring at grain boundaries, but also provide abundant active sites, resulting in excellent HER catalystic performance (overpotential is 184 mV at 10 mA cm^-2 and Tafel slope is 78.4 mV dec^-1).<br/>In this study, we presented a new strategy to improve the performance of the HER through GBs density control using a pulsed laser.