Electrochemical deposition of thin bifunctional Co-P films and investigation of their electrocatalytic and corrosion properties in the hydrogen evolution reaction and oxygen evolution reaction

At present, the rapid growth of the global economy, together with the accelerated depletion of fossil fuel resources, has led to growing concerns about the availability and sustainability of energy. Therefore, renewable energy sources such as solar, hydrogen, and wind energy are of critical importance. Compared with other hydrogen production methods, water electrolysis offers several advantages, including sustainability, low cost, high efficiency, and the absence of harmful atmospheric emissions. In recent decades, water electrolysis as a hydrogen production technology has been extensively investigated. The development of new, efficient, and cost-effective electr­ocatalysts for water electrolysis remains a crucial challenge. Cobalt-phosphorus thin films are promising candidates for replacing expensive noble-metal-based electrocatalysts. In the present work, bifunctional Co-P thin films were synthesized via a one-step electrodeposition method from an acidic electrolyte. The as-deposited films were amorphous; however, after annealing, two ortho­rhombic phases, Co₂P and CoP, were identified by X-ray diffraction analysis. The prepared films were characterized using X-ray phase analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The electrocatalytic properties of the coatings were investigated before and after annealing in both neutral (0.5 M Na₂SO₄) and alkaline (1 M KOH) media for the hydrogen and oxygen evolution reactions. In addition, the corrosion behaviour of the Co-P thin films was examined, and it was established that the amorphous, non-annealed films exhibited superior corrosion resistance in alkaline media.