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 x P (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 x P 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 x P.