Phase Transition Assisted Photo-, Electro- and Photoelectrocatalytic Hydrogen Evolution in B/MoS<sub>2</sub>─Mechanistic Insight
Daria Baranowska, Tomasz Kędzierski, Grzegorz Leniec, Beata Zielińska, Ewa Mijowska
Abstract
High Resolution Image Download MS PowerPoint Slide Electrocatalytic water splitting is recognized as one of the most effective methods for sustainable hydrogen production, with visible light integration recently emerging as a promising enhancement strategy. To address this, we developed a 2D/2D heterostructure of borophene and molybdenum disulfide (B/MoS 2 ) to investigate its efficiency in photo-(photo), electro-(HER), and photoelectro-(PEC) catalytic hydrogen evolution reactions under acidic conditions. Optimizing the MoS 2 -to-boron mass ratio revealed significantly reduced overpotential, achieving 281.1 mV and a Tafel slope of 56.0 mV/dec in PEC, compared to 312.5 mV and 160.9 mV/dec in conventional HER, indicating boosted activity and kinetics of the hydrogen evolution process. Additionally, a long-term stability test at a constant current density of 10 mA/cm 2 confirmed the high durability of B/MoS 2 and maintained stable performance for up to 120 h. The B/MoS 2 demonstrated an improved hydrogen evolution rate reaching ∼2.5 mol/g in PEC, representing a 1.4-fold, 1.8-fold, and 3152-fold increase compared to pristine MoS 2 in photoelectro-, electro-, and photocatalytic hydrogen evolution process, respectively. Moreover, comprehensive material characterization elucidated the underlying PEC mechanism, including in situ and ex situ analyses. It highlighted the potential of borophene-enriched MoS 2 as an efficient catalyst for solar and/or electricity-driven hydrogen production, confirming that borophene presence substantially promotes the 2H-to-1T phase transition of MoS 2 by creating strain and defects, destabilizing the 2H phase, and favoring the formation of the 1T phase, thus significantly enhancing catalytic performance. Interestingly, the 2H-to-1T phase transition of MoS 2 is detected in all three processes: photo-, electro-, and photoelectrocatalytic hydrogen evolution reactions. However, its efficiency follows the order: PEC > HER > photo indicating that visible light irradiation is a missing activity descriptor revealing a puzzle of hydrogen evolution mechanism during PEC water splitting.