Preparation Of Carbon-Based Non-Noble Metal Catalysts And Their Applications In Hydrogen Evolution Reaction

Environmental issues have been turned to be one of the major problems during the current world development process.The sustainable energy supply has been proved to be essential to the social development.At present,the most widely used energy sources are still dominated by traditional fossil energy sources,and the use of fossil energy sources can cause serious environmental problems such as acid rain,greenhouse effect,and ozone holes.Therefore,it is particularly important to develop sustainable,green and friendly clean energy.Hydrogen is the most abundant element in nature,and the combustion value of hydrogen is much higher than traditional fossil energies.Most importantly,the final product of hydrogen combustion is only water,which is a real green energy.Among all the currently developed strategies,electrocatalytic decomposition of water has been proved to be a simple method to produce hydrogen with high purity.The required electricity in the catalytic process can directly use the off-peak power in the power supply system as well as unstable solar-produced electricity and wind-generated electricity,which are less stable but are of low cost.Rational use of these unstable electric energy and converse it into hydrogen energy for storag.To maintain the high catalytic performance of catalytic materials with low costs,this paper employs non-precious metals that are cheap and easily available.In addition,carbon materials were used as carriers to reduce the metal content.The highly-efficient non-precious metal carbon-based composite electrocatalysts were synthesized by a simple and easy preparation method,and the catalysts were well characterized and employed in HER process.Firstly,graphene was employed as the support and PVP as the nitrogen source and template to grow cobalt and nickel ions onto the surface of graphene by high temperature calcination.A carbon-coated CoNi@N-C/rGO-n composite catalytic material was successfully prepared and further applied in HER process in acidic solution.Among the prepared catalysts,CoNi@N-C/rGO-3 holds an exchange current density and maintains good stability.It was found that the nitrogen-doped carbon layer provides an excellent protection to the cobalt-nickel alloy nanoparticles,while the graphene promoted the catalytic reaction.A series of CoNi@N-C/rGO-n composite catalytic materials were further obtained by adjusting the graphene amount.Compared with the catalytic properties of CoNi@N-C,N-C/rGO and rGO,it was found that graphene can effectively promote the catalytic performance.The efficient charge transfer was also increased during the process.At the same time,the synergy between cobalt-nickel alloy nanoparticles and graphene is also an important factor to the improvement of the HER performance.The effects of electrolyte temperature and scanning rate on the HER performance were also investigated.The experimental results showed that the increase of electrolyte temperature has a significant effect on the Tafel slope,and the effect of scanning rate on Tafel slope is not obvious.In addition,a novel metal carbide was further prepared as a highly-active HER catalyst.The CTAB surfactant was used as the nitrogen source for dispersion of Fe ions and Zn ions in solution.Since there are numerous oxygen-containing functional groups on the surface of the graphene oxide,the metal ions can be well adsorbed onto the surface.The thin layer structure of graphene oxide was frozen dried and further carbonized in a nitrogen atmosphere at 600^oC to obtain Fe₃ZnC@N/rGO-n catalysts,surpisingly.As an electrochemical HER catalyst,it holds an exchange current density and maintains good stability.Additionally,XRD,XPS,Raman,BET and some other characterizations showed that the Fe₃ZnC exhibited an excellent HER catalytic performance.By adding appropriate amount of graphene,the HER performance can be boosted remarkably.The increased HER activity is attributed to the synergy between the nitrogen-doped graphene and Fe₃ZnC and the excellent charge transfer.The effects of electrolyte temperature and scanning rate on the catalytic performance of HER were investigated.The experimental results show that the increase of electrolyte temperature has a significant effect on the lowering the Tafel slope,but the effect of scanning rate is not obvious.Furthermore,the morphology was further controlled by adjusting the prescusors.During the preparation process,the layered structure of graphene was preserved by a freeze-drying method,and then calcined in an inert gas atmosphere at 600°C to obtain a three-dimensional flower-like Co/ZnO@N/rGO-n catalysts material.The HER activity of the three-dimensional Co/ZnO@N/rGO-n composite in an acidic solution is very nice,and a good stability during the10-hour i-t test was obtained.Comparing the HER catalytic properties of Co/ZnO,ZnO@N/rGO and N/rGO,it was found that the high HER catalytic activity of the composite catalytic material is originated from the combination of chemical interaction and electronic synergy between Co/ZnO and N/rGO.The conclusion was supported by XRD,Raman,BET and other characterizations.The effect of electrolyte temperature and scanning rate on the catalytic performance of HER was further investigated.The experimental results showed that the scanning rate has little influence on the HER activity,and the increase of electrolyte temperature can obviously increase the HER performance.Then,we tried to prepare carbon nanotubes on the surface of rGO to form a confining effect for an enhanced catalytic performance and stability.In this section,a nickel induced carbon nanotubes on the graphene were developed by a one-step calcination method to obtain a HER catalytic material(Ni-Ni₁₂P₅@CNT/rGO-n).The products at different temperatures were investigated to determine the formation process.Among them,the obtain of elemental nickel was obtained by the reduction of dicyandiamide.The elemental nickel played an important role in the formation of carbon nanotubes the improvement of HER activity.When the total nickel content was 0.5 mmol,the HER performance is better than others.In addition,the catalyst maintained a good stability within 10 hours.The electrolyte temperature and scan rate also have a key effect on the catalytic HER performance.The experimental results showed that the increase of electrolyte temperature can significantly reduce the Tafel slope.The CV cycling and i-t tests showed that the Ni-Ni₁₂P₅@CNT/rGO-0.5 has a good stability.Lastly,the above-mentioned strategy was further employed in a cobalt-based catalytic system,that a single-sided graphene surface growed phosphating cobalt-catalyzed carbon nanotube composite HER catalytic material?Co-Co₂P@CNT/rGO-n?was obtained by a one-step calcination process.During the preparation process,dicyandiamide can reduce part of cobalt ions into elemental cobalt,and conclusion was experimentally proved.In order to verify the effect of elemental cobalt,a Co₂P@CNT/rGO composite catalyst material was obtained by replacing the carbon source in the precursor.The HER performance of the composite catalyst was adjusted by adjusting the content of cobalt.When the total content of cobalt reached 0.7mmol,the performance of Co-Co₂P@CNT/rGO-0.7 was the most excellen.Compared with Co₂P@CNT/rGO,the boosted HER performance was originated from the synergy between cobalt phosphide and carbon nanotubes and graphene.The effect of electrolyte temperature and scanning rate on the catalytic performance of HER was also investigated.The increase of electrolyte temperature significantly lowered the Tafel slope,while the effect of scanning rate is not significant to the HER activity.The Co-Co₂P@CNT/rGO-0.7 composite catalytic material also has a good stability during CV cycles and i-t test.