| Hydrogen,with high calorific value and reproducibility,has been considered to be the cleanest energy source.The earth has abundant water reserves,and the method of preparing H2 and O2 by electrolyzing water(2H2O 2H2+O2)is considered to be the most direct and clean way.The best catalysts today are precious metals Ir and Ru,as well as their derivatives;however,their large scale applications are seriously hampered by their high cost,high scarcity and poor durability.Studies found that photothermal effect of metallic electrocatalysts will promote the mass transfer process and facilate the water splitting.Therefore,it is a good strategy to prepare efficient OER catalyst and apply it under light-assisted irradiation.In this paper,crystalline structured cobalt-based borides and carbides were prepared using ball milling method.They were further studied as OER catalysts in electrical/optical-assisted water-splitting devices.The main research contents are as follows:1.Crystalline CoB,Co2B and Co3B were prepared by ball milling method.Among these catalysts,Co2B exhibits the best OER performance due to its favorable Co content and the special structure.Benefited from this,it needs 287 mV overpotential to drive 10 mA cm-2 in a 1 mol L-1 KOH solution and maintains stability for 12 hours.Especially,the OER activity of Co2B is significantly enhanced with the aid of light,and the reasons for which was analyzed base on its light absorption characteristics2.Crystaline bimetallic(NixCo1-x)2B particles were prepared by ball milling method and were used as OER catalysts.For the first time,the chemical origins were identified by analyzing differences in hydrophilic and hydrophobic environment,and revealed that the enhanced activity of bimetallic boride is the activation of Co catalytic center by Ni element.Benefited from this,the prepared(Ni0.75Co0.25)2B can drive a current density of 10 mA cm-2 in a 1 mol L-1 KOH solution with overpotential of only 224 mV.In addition,the catalyst has an enhanced effect under light-assisted irradiation.We analyze the gain mechanism of OER according to the physical intrinsic characteristics of the material.3.Crystaline Co3C based material was prepared by ball milling method.In this work,NaBH4 was used to soak N-containing Co3C at room temperature,and the anchoring of N to B was used to achieve the first B doping under low temperature conditions.Benefited from the regulation of the electronic structure of the Co metal center by B and N,Co3C-NB obtained an improved OER and HER activities.It can drive OER and HER to current densities of 10 mA cm-2 with small overpotential of 358 mV and 154 mV in 0.1 and 1 mol L-1 KOH solutions,respectively.Based on the intrinsic ORR activity of Co3C,a solid-state Zn-air battery selfpowering a full water splitting system using a Co3C-NB electrode as the air cathode and anode was constructed,which realize the combination of these two systems.In addition,with the aid of light,the OER activity of Co3C-NB was further improved,and the enhancement mechanism of OER was analyzed according to its physical intrinsic characteristics.4.Crystaline(NixCo1-x)3C bimetallic catalysts was prepared by ball milling method.To drive a current density of 10 mA cm-2 in a 1 mol L-1 KOH solution,(Ni0.4Co0.6)3C needs only 323 mV overpotential,and which can be further decreased under light-assisted irradiation.The reasons for the enhancement of OER were analyzed according to the physical intrinsic characteristics of the material.Briefly,Co2B possesses considerable OER activity,where the activity of the Co catalytic center can be further enhanced by the activation of another metal Ni.In contrast,the intrinsic OER performance of Co3C is not as good as Co2B,but it can be improved by co-doping non-metallic B and N or introducing metal Ni.Both these two kinds of materials can absorb light in the visible light range,and can promote the mass transfer process through photothermal action,thus facilating water splitting. |
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