Iron Phosphide Nanobundles for Efficient Electrochemical Hydrogen Evolution Reaction in Acidic and Basic Media

Earth-abundant transition metal phosphide (TMP) nanomaterials have gained significant attention as potential replacements for Pt-based electrocatalysts in green energy applications, such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting. In particular, FeP nanostructures exhibit superior electrical conductivity and high stability. Moreover, their diverse composition and unique crystal structures position FeP nanomaterials as emerging candidates for HER electrocatalysts. However, the synthesis or fabrication method employed for FeP nanostructures can significantly affect their overall electrocatalytic properties. For example, the solution synthesis of pure-phase FeP nanostructures remains challenging due to the formation of multiple binary phases and undesirable agglomeration. In this work, we use a simple approach to synthesizing FeP nanobundles by reacting β-FeOOH (iron oxyhydroxide) with trioctylphosphine (TOP). FeP nanobundles were evaluated as HER electrocatalysts in both acidic and basic conditions, demonstrating good HER activity with overpotential values of 170 and 338 mV at a current density of -10 mA cm^-2 in acidic and alkaline solutions, respectively. Additionally, they exhibited low values of Tafel slopes in both acidic and alkaline environments. In acidic media with a pH of 0.45, the nanobundles showed no signs of deterioration for up to 15 h (-50 mA cm^-2). In basic media with a pH of 13.69, the nanobundles remain stable for up to 8 h (-50 mA cm^-2). These results demonstrate a simple and effective method for producing highly efficient earth-abundant and cost-effective TMP-based electrocatalysts, which could play a vital role in the hydrogen economy of the future.