Controllable Synthesis Of Ruthenium Phosphides?RuP And RuP₂? Their Performance In PH-universal Hydrogen Evolution Reaction

Hydrogen?H₂?is a sustainable and environmentally friendly fuel,and electrocatalytic reduction of water is an effective method to produce H₂ via hydrogen evolution reaction?HER?.Metal phosphides are promising efficient non-Pt electrocatalysts for hydrogen evolution reaction.In this study,we report a simple strategy to controllably synthesize RuP and RuP₂ and evaluate their HER performances in all pH range.The main results are summerized as follows:?1?Firstly,the pure RuP and RuP₂ could be selectively synthesized through a simple heat-treatment in different temperatures at H₂ atmosphere.The possible reaction mechanism between RuCl₃ and NaH₂PO₂ in H₂ and insert atmosphere was discussed.XRD pattern shows that temperature and gas atmosphere play a very important role in the synthesis.The pure phase of RuP₂ was synthesized at temperature above 500°C in H₂.When the temperature was between 425°C and 500°C,the pure phase of RuP was prepared.In contrast,the resulting product was a mixed phase of RuP and Ru₂P when hydrogen?H₂?was adjusted to an inert gas?N₂?.Then the samples were characterized by SEM,TEM and XPS,indicating the successful synthesis RuP and RuP₂.?2?The HER performance of RuP_x-N was systematically evaluated in all pH range.It is found that the RuP-475 exhibits the excellent HER performance in all pH range,especially in neutral and alkaline conditions.The RuP-475 exhibits excelent HER performance with small overpotential at a current density of 10 mA cm^–2?46,47,22mV in pH=0,7,and 14,respectively?.Besides,RuP-475 presents better HER performance than RuP₂-550 in all pH range,and RuP-475 has superior stability in a long-time electrochemical process and CV tests in all pH range.?3?The reason why RuP-475 presents better HER performance was systematically explored.The BET surface areas of RuP-475 and RuP2-550 measured by N2 adsorption and desorption are very close.Electrochemically active surface area?ECSA?test by using a typical CV method shows that RuP-475(16.2 mF cm^–2)exhibits the larger value of Cdl than RuP₂-550(3.0 mF cm^–2),indicating that RuP-475 exposes more active sites than RuP₂-550.Furthermore,the electrochemical impedance spectroscopy?EIS?analyses of RuP-475 and RuP₂-550 were also tested.And the RuP-475 catalyst shows a much smaler charge transfer impedance(R_ct=173?)than RuP₂-550(R_ct=1544?),indicating that the better electron transferring ability of RuP-475.In summary,the RuP-475 with more Ru had much better conductivity and more catalytically active sites than the P rich RuP₂-550.