Ruthenium Phosphide Synthesis and Electroactivity toward Oxygen Reduction in Acid Solutions

Ruthenium phosphides are known to be highly stable and conductive materials. A new process was developed to prepare ruthenium phosphide catalysts for oxygen reduction in acid solutions. Several synthesis methods have been applied to form pure RuP and Ru₂P as well as mixed phases of Ru and Ru_xP (x ≥ 1). These methods utilize high-temperature solid-state synthesis and reaction under autogenic pressure at elevated temperature (RAPET). On the basis of rotating ring-disk electrode (RRDE) experiments, oxygen reduction activity was observed on all Ru_xP materials. Characteristic kinetic parameters show specific exchange current densities in the range of 0.4-1.4 mA mg^-1, Tafel slopes of 129-135 mV dec^-1, and %H₂O₂ of 3-11% of the total current. Complementary XPS and Raman spectral analysis reveals a highly oxidized surface with significant presence of PO₄^3- and RuO₂ species. To the best of our knowledge, this is the first report identifying oxygen reduction activity on Ru_xP.