Synthesis Of Heteroatom Doped Carbon Based Materials For Photo/Electro-catalytic Applications

The energy crisis caused by the depletion of fossil fuels is a serious problem to be solved in human society.The photo/electro-catalytic hydrogen production technology based on new materials is one of the most effective ways to solve the energy issues,and has received extensive attention in recent decades.The development of new efficient and low-cost non-noble metal catalysts that favor high photo/electro-catalytic performance is of great significance toward industrial application of hydrogen production.In this thesis,the preparation of heteroatom doped-carbon materials based composites and their photo/electro-catalytic hydrogen production performance were studied.Firstly,nitrogen and sulfur co-doped reduced graphene oxide?NS-rGO?was synthesized using a low temperature calcination method,which was then used as support and cocatalyst for the anchor of CdS to construct highly efficient CdS/NS-rGO binary composites.The CdS/NS-rGO exhibit high photocatalytic activity for hydrogen evolution and 4-NP reduction under visible light???420 nm?.Their activity could also be adjusted by changing the doping amount of S and N,or by changing the ratios between CdS and NS-rGO.The optimum percentage of NS-rGO is 5wt%,at which CdS/NS-rGO photocatalyst could achieve the highest H2 evolution rate of 1701?mol·h^–1·g^–1.Moreover,the reduction from 20 ppm of 4-NP to 4-AP could be completed within only 6 min over this optimized composite.Based on the experiment and DFT calculations results,we believe that the enhancement of photocatalytic activity is due to the better charge separation efficiency,wider light absorption range and decreased H*absorption free energy,better charge separation efficiency,wider light absorption range,smaller band gap,and decreased H*absorption free energy.In the second part,we report a one-step facile synthesis of a novel precious metal-free hydrogen evolution electrocatalyst Mo₂C/NP-C using starch and ammonium molybdate as precursors,ammonium nitrate as nitrogen doping and pore forming agent,which is composed of Mo₂C nanoparticles uniformly embedded within nitrogen-doped porous carbon?NP-C?layers.The results show that the Mo₂C/NP-C hybrid has a remarkable electrocatalytic activity toward hydrogen evolution reaction over a wide pH range?pH 0¹4?.The best catalytic performance of HER was obtained at a 1:1 ratio of precursors and 0.3 g amount of NH₄NO₃.Especially under alkaline conditions,the Mo₂C/NP-C hybrid afforded a current density of 10 mA·cm^–2 at relatively low hydrogen evolution overpotential of 101 mV vs.RHE.Furthermore,the reasons for NP-C enhanced electrocatalytic activity were also briefly discussed.By characterization analysis,we found that the improvement of catalytic activity of the composite was attributed to the large specific surface area induced by the porous structure and the decrease of interface impedance after doping.Based on the above two work,we have developed two non-prevcious catalysts with high catalytic activity for photo/electrocatalytic hydrogen evolution,which has a good application prospects due to their cost efficiency,simple preparation steps.In addition,we further deeply discussed their activity enhancement mechanism providing necessary theoretical basis for further optimization of catalysts.