Preparation Of Metal Phosphide Nanomaterials And Their Catalytic Performance For Hydrogen Production

With the energy crisis and the increasingly serious environmental pollution problems, the development of renewable energy has become a global consensus. As a kind of clean and renewable resource, hydrogen is believed to be one of the most promising alternative energy carriers. Therefore, hydrogen is attracting more and more attention. Among numerous hydrogen production technologies, the production of hydrogen through water splitting is potentially of great importance in solving the energy crisis and environmental problems. Hydrogen can be generated by electrolysis or photoelectrolysis of water. Effective electrocatalysts for HER are essential for efficient hydrogen generation from electrolysis and photoelectrolysis. The efficient hydrogen evolution electrode should have high electrical conductivity, large surface area, low hydrogen evolution overpotential, high catalytic activity, good electrochemical stability, corrosion resistance, and etc. At present, noble metal nanoparticles（e.g. Pt） have shown to possess excellent catalytic activity for the HER,while the scarcity and high cost are likely to limit their broader application. Effective low-cost catalysts for the HER are therefore highly desirable.In this paper, the nickel phosphide（Ni₃P） porous hollow nanospheres（PHNs）,Co₂ P nanosheet（Co₂P/CuFoam）, and Molybdenum phosphide（Mo P） flakes electrode have been produced by different synthesis methods, and the crystal structures and the hydrogen evolution activity have been studied. The research achievements are listed as follows:（1） A facile and scalable approach was developed to synthesize nickel phosphide（Ni₃P） porous hollow nanospheres（PHNs）. The formation of the Ni₃ P PHNs was correlated with phase separation during the thermal annealing of the amorphous nickel-phosphorus nanospheres that affords crystalline Ni-Ni₃ P nanoparticles and the subsequent selective removal of nickel. The Ni₃ P PHNs show effective catalytic activity in the hydrogen evolution reaction. The overpotential required for the current density of 20 mA cm-2（η20） is as small as 99 mV in acidic solution and 338 mV in basic solution. The performance is comparable than that of other metal phosphides,and is superior to that of transition metal dichalcogenides, carbides, borides, and nitrides. The faradaic efficiency of the Ni₃ P PHNs is nearly 100%, and the Ni₃ P PHNs are stable during the long-term electrolysis of water. The scalable production, low cost,excellent catalytic activity, and long-term stability afford promising applicationpotential for the Ni₃ P PHNs.（2） A highly efficient bifunctional catalyst was introduced for both OER and HER, which was prepared via electrodeposition of mesoporous amorphous Co-P nanosheets onto macroporous CuFoam substrates without using chemical binders followed by thermal annealing and HCl etching. The Co₂P/CuFoam electrode can offer large active surface area, fast mass transport and fast electron transport in the electrode. The 20 mA cm-2 and 80 mA cm-2 is as small as 146 and 188 mV in acidic,with prominent durability under high current densities. As oxygen evolution electrode,the highest catalytic activity of Co₂P/CuFoam is obtained in a j of 100 mA cm-2 at an overpotential of 310 mV Co₂P/CuFoam is an ideal dual function material.（3） Molybdenum phosphide（Mo P） flakes were synthesized by the reduction of hexaammonium heptamolybdate tetrahydrate and ammonium dihydrogen phosphate.The flakes are porous and constructed by Mo P nanoparticles with ca. 100 nm diameters. The lateral size of flakes ranges from less than 1 μm to larger than 5 μm,and the thickness of Mo P fakes is ca. 200 nm. The mixture of Mo P flakes and carbon black exhibits effective catalytic activity in the hydrogen evolution reaction. The require overpotential required for 20 mA cm-2 current density is 155 mV in acidic solution and 184 mV in basic solution. The mixture can work stably in long-term hydrogen generation in both acidic and basic solution. The faradaic yield of mixture in hydrogen evolution reaction is nearly 100% in both acidic and basic solution. The Mo and P species in MoP flakes are found to have small positive and negative charge respectively. The catalytic activity of Mo P flakes is likely to be correlated with the charged nature.