Synthesis Of Free-standing Nickel-based Cayalysts And Study Of Electrocatalytic Performance

In recent years,renewable energy sources such as solar energy and wind energy have been widely used in our daily life.However,these types of energy are subject to daily and seasonal intermittent and regional changes.That is to say,the current energy storage technology is not perfect,may restrict or reduce the efficiency of the use of these energy,leading to a series of energy shortage problems.One of the best ways to solve this problem is to convert unstable electric energy into stable chemical energy.As a relatively stable energy with high energy density,hydrogen energy can meet these demands.Electrocatalytic decomposition of hydrogen production is an important means of hydrogen production,and the other half reaction oxygen production reaction can also be used to produce a large amount of oxygen,is a green,efficient and pollution-free clean energy.Although precious metal elements such as Pt,Ir and Ru have good catalytic performance,their high price,rare earth reserves and difficult mining limit the large-scale application and commercialization of catalysts.Transition metals are relatively cheaper and abundant resources on the earth is expected to be low and high efficient catalyst.Ni-based catalysts have relatively good electrical conductivity.The surface of the rich in reserves and more easily obtained.As a result,the transition of development studies with cheap and have potential performance base catalyst materials is particularly important.In view of the above problems,this paper firstly summarizes the design principles that need to be considered for the low cost and high efficiency preparation of water decomposition catalyst.Firstly,in order to reduce the cost,the catalyst material was selected as Ni-based catalyst.Secondly,because the traditional coating method is easy to fall off the catalyst and the stability is not good enough,the process is more complicated,so the method of in-situ growth is chosen to prepare the catalyst.Finally,because bifunctional catalysts can save production costs and there are still few catalysts suitable for bifunctional catalysis,we decided to prepare bifunctional total water decomposition catalysts.First,consider the space for the introduction of the active site and its influence to the electronic structure,this paper adopted the carbon cloth as the base,using hydrothermal method,chemical vapor deposition method and the method of sodium borohydride reduction was prepared in situ Ni sulfide catalysts,by process parameters optimization to determine the best time to restore,success in getting the introduction of the sulphur vacancy NiS catalyst.The obtained samples can reach the current density of 10mAcm^-2 at 164mV for HER,26mV lower than that without the introduction of S vacancy.And 10mAcm^-2 at 240mV for OER,44mV lower than that without the introduction of S vacancy.And the current density of 10mAcm^-2 at 1.67 V for total water splitting.By means of X-ray photoelectron spectroscopy,the peak of Ni 2P is determined to have a large shift,which shows the regulating effect of vacancy introduction on the electronic structure.Density Functional Theory calculation further shows that the sulfur vacancy can increase the charge density of the corresponding sites,which is conducive to the improvement of the electron transport efficiency of the corresponding sites,so as to improve the electrical conductivity of the sample.The introduction of sulfur vacancy is more conducive to the absorption and desorption of H⁺,thus enhancing the intrinsic activity of the active sites.Furthermore,in order to further simplify the synthesis,increase the water splitting performance of the sample and prepare the bifunctional catalyst,polyvalent vanadium element was introduced,and a heterojunction catalyst strategy containing Ni and V metal cations was proposed.Self-supported NiS/VS catalysts were synthesized in situ by hydrothermal method and chemical vapor deposition.The catalyst still maintains the morphology of nanosheet after the introduction of vanadium.The interface of heterostruture brings strong electron interaction,which is beneficial to the improvement of catalytic performance.At the same time,the introduction of polyvalent vanadium brings more exposed active sites,which in turn improves the catalytic activity.NiS/VS showed excellent catalytic performance,and the current density of 10mAcm^-2 could be reached with only 158mV overpotential on the HER side,and the overpotential of OER was 240mV.The current density of 10mAcm^-2 at a low voltage of 1.64 V can be achieved when NIS/VS is present in a two-electrode cell for water splitting.Finally,in order to avoid the use of long process time,more by-products,high pollution,high energy consumption of the synthesis strategy,the synthesis method and synthesis route were optimized.The introduction of Rh element,through a simple in-situ etching method of preparation of Ni-based catalyst.The introduction of Rh leads to the improvement of catalytic performance.The rough surface improves the active surface area of the sample,which is conducive to the exposure of active sites.The current density of 10mAcm^-2 can be achieved with only 65mV overpotential for HER It was 169mV lower than that without Rh.On the OER side,the current density of 10m A cm^-2 can be reached with only 260mV,which is 103mV lower than that without the introduction of Rh.The current density of 10mAcm^-2 can be reached with only1.56 V when it is used for water splitting,showing excellent performance of total water splitting.In view of the high cost and poor applicability of in-situ self-supported catalysts,this paper provides a very useful experience for the rapid synthesis of high efficiency nickel-based bifunctional total water decomposition catalysts.