Unveiling the formation of bismuth silicate phase through thermal annealing and application for enhanced hydrogen evolution reaction

Abstract Earth-abundant electrocatalysts for the alkaline hydrogen evolution reaction (HER) need to offer low overpotentials, good stability and scalability. Bismuth-based materials are a promising non-noble alternative electrocatalyst because of their good electrochemical characteristics. This research explores the phase transformation of a bismuth system by means of thermal annealing to form bismuth silicate (Bi 2 SiO 5 ) as the major phase. Precursor samples were prepared using a solvothermal reaction and then annealed at temperatures of 400°C, 600°C, 800°C and 1000°C. X-ray diffraction studies showed that Bi 2 SiO 5 with pure phase and sharp diffraction peaks is formed by annealing at 600°C, at which temperature phase stabilization occurs. Annealing at higher temperatures leads to partial decomposition and phase distortion, likely caused by distortion of the silicate structure. Electrochemical HER measurements conducted in 1 M KOH solution shows that the (BSO-600) catalyst exhibits best performance with overpotential of 104 mV at 100 mA cm −2 and a Tafel slope of 31.4 mV dec −1 , suggesting effective charge transfer and fast reaction kinetics. Electrochemical impedance spectroscopy indicated a low charge transfer resistance (Rct) of 0.69 Ω (compared to nickel foam at 15.2 Ω and Pt/C at 3.85 Ω), implying good conductivity and robust interaction with HER intermediates. This was confirmed by cyclic voltammetry, showing a high electrochemically active surface area (ECSA) 242.3 cm 2 for BSO-600, with improved surface accessibility. In conclusion, this study suggests bismuth silicate as a promising material for alkaline HER and phase engineering as an important factor in catalyst design.