Bifunctional Phosphide Catalysts With Ultralow Amount Of Noble Metals

The energy density of hydrogen is 2-3 times higher than that of fuel oil.Developing hydrogen fuel cell is an important method to solve the problem of current energy shortage and environmental pollution.Fuel cells can directly convert chemical energy into electrical energy,which is not restricted by the Carnot cycle.At the same time,the reaction process is noiseless and the products are not polluted.It is a clean and efficient energy conversion device.The research of HER and fuel cell catalysts is also a hot issue that attracts much attention.The commonly used catalysts are Ir and Pt based catalysts.But,the price and reserves of noble metal have limited our large-scale application.However,noble metal catalysts have significant advantages compared with other catalysts,which is our most efficient choice for catalytic work.Therefore,we need to reduce the load of precious metals,and at the same time improve the catalyst recovery ability and stability.Ultra-low precious metal catalyst is one of the main current research trends of hydrogen evolution reaction（HER）and oxygen reduction reaction（ORR）.Therefore,two metal phosphide catalysts with low noble metal loading,high catalytic efficiency,and a wide range of applications were proposed.Results of the innovative researches are as follows:（1）A synthesis method of PtP₂@PC nanocatalyst with ultra low Pt loading has been reported,and applied the catalyst to the hydrogen evolution reaction for the first time.The synthesis method is as follow:Chloroplatinic acid was poured into phytic acid solution,with ultrasonic dispersion.The mixture was heated by the tube furnace.In the electrochemical test,PtP₂@PC-2.35 only needs an overpotential of 23 m V to drive a cathode current density of 10 m A/cm²,which is 10 m V lower than Pt/C（33m V）.Its Tafel slope is 30.8 m V/dec,which is close to the Tafel slope of Pt/C.It is worth noting that the electrocatalytic activity of the PtP₂@PC-2.35 remains stable for 50,000s continuous electrolysis at a constant potential,indicating that the catalyst has a good endurance stability.Besides,in the oxygen reduction reaction test under alkaline conditions,the half-wave potential of PtP₂@PC-2.35 is very close to the commercial Pt/C catalyst,indicating that the catalyst also has an excellent ORR performance.（2）In view of Ir-based catalysts are also widely used in the field of electrocatalysis,according to the above method,by changing the metal source,a phosphorus-doped carbon-coated IrP₂ catalyst（IrP₂@PC）with Ir content only 1 wt%was synthesized.It has very high HER performance,exceeding commercial Pt/C and most reported transition metal catalysts across the entire p H range.In alkaline electrolyte,only 10m V overpotential is needed to reach the current density of 10 m A/cm²,the Faraday efficiency of hydrogen production is close to 100%.At the same time,in acidic and neutral electrolytes,only 15 and 32 m V are required to reach the current density of 10m A/cm².It is worth noting that in the oxygen reduction reaction test under alkaline conditions,the half-wave potential of IrP₂@PC is 0.81 V,which is very close to the commercial Pt/C catalyst,indicating that the catalyst also has an excellent ORR performance.Comparison of high-power transmission electron microscope and XPS patterns before and after 3000 cycles showed that the IrP₂@PC catalyst had high electrochemical stability during the acceleration of HER.