Application Of 3D Printed Hierarchical Porous Graphene Based Electrodes In Water Splitting

Hydrogen energy is considered as the cleanest renewable energy at present,and it is one of the most important parts of the future energy system.The development of sustainable hydrogen production technology is critical to the future hydrogen energy economy.The hydrogen production technology by water splitting has received extensive attention and research due to the feature of green,simple and sustainable.The development of highly efficient electrocatalytic electrodes which can reduce the consumption of electrical energy in the production of hydrogen by water splitting is a very critical and extensively studied scientific issue in the field of hydrogen production by water splitting.Increasing the number of active sites on the electrocatalytic electrodes is an important strategy to improve the performance of water splitting and reduce energy consumption.Compared with traditional planar electrodes,three-dimensional(3D)bulk electrodes have become a research hotspot due to more active sites provided by their large surface area.However,the current 3D bulk electrodes are always limited in thin thickness by the demand of rapid mass transport in the water splitting process.Due to insufficient mass transfer speed,thick 3D bulk electrodes have the limitation in the effective utilization of the electrode's internal surface area and have no greater performance improvement compared with thin electrodes.Therefore,it is urgent to prepare a three-dimensional thick electrode with highly quality transfer speed to make full use of the internal surface area for increasing the active sites and greatly improve the performance of water splitting,which is still a challenge in the field of water splitting.In order to solve the above problems,we have used 3D printed graphene/carbon nanotube three-dimensional electrodes(3DP GC)with high conductivity and hierarchical porous structure to construct macro-micro hierarchical porous 3DP GC/NiCoP and 3DP GC/NiFeP three-dimensional self-supporting electrocatalytic electrodes by in-situ growth of NiCoP and NiFeP nanocatalyst arrays respectively in this paper.In water splitting,due to the macroscopic and microscopic porous structure,3DP GC electrodes can achieve faster mass transfer than the traditional bulk electrode as well as better performance than porous traditional bulk electrodes.In addition,the performance of water splitting can be significantly improved by a simple strategy to increase the thickness of the electrode and effectively increase the number of active sites.Detailed research contents and results are as follows:(1)3DP GC/NiCoP electrocatalyst electrodes were prepared by in-situ growth of NiCoP nanowire array on the high conductivity and hierarchical porous 3DP GC electrodes.The electrocatalyst electrodes conduct excellent catalytic performance for hydrogen evolution reaction and the overpotential was only 107 mV at a current density of 10 mA/cm2 in alkaline medium.Moreover,as-prepared 3DP GC/NiCoP electrocatalyst electrodes have good stability.(2)3DP GC/NiFeP electrodes were prepared by in-situ growth of NiFeP nanosheet arrays on the hierarchical porous and high conductivity 3DP GC electrodes.The prepared electrodes achieved efficient bifunctional water splitting.In alkaline of HER,the 3DP GC/NiFeP electrocatalyst electrodes have the overpotential of 149 mV at a current density of 10 mA/cm2.In alkaline of OER,the 3DP GC/NiFeP electrocatalyst electrodes have the overpotential of 234 mV at a current density of 10 mA/cm2.(3)We have achieved highly efficient overall water splitting by a simple strategy,which increase the thickness of the electrode and to effectively increase the number of active sites.Taking advantage of the rapid mass transfer,high conductivity and large specific surface area of the 3DP GC electrodes,we have prepared 3DP GC/NiFeP electrodes with different thickness by the in-situ growth of NiFeP nanosheet arrays on 3DP GC electrodes with different thickness.We use 3DP GC/NiFeP electrodes of different thickness directly as anode and cathode in double electrode electrolyzer.We have further improved the catalytic performance of the 3DP GC/NiFeP electrodes by a simple strategy to increase the thickness of the electrode and effectively increase the number of active sites.A low cell voltage of 1.58 V was required for 3DP GC/NiFeP-24L double electrode electrolyzer to obtain current density of 30 mA/cm2.It has achieved highly efficient and stable overall water splitting.In summary,the graphene/carbon nanotube three-dimensional electrode with hierarchical porous structure prepared by 3D printing technology is used in water splitting.The advantages of the 3DP GC/NiCoP electrocatalyst for water splitting are as follows:(?)High conductivity of the hierarchical porous 3DP GC electrodes are beneficial to the rapid electron transfer during the electrocatalytic process.The hierarchical porous structure provides a large specific surface area and rapid mass transfer capability.And the network skeleton with large pore channels can make electrolyte and gas diffuse smoothly.(?)Direct in-situ growth of highly active NiCoP and NiFeP catalysts on the 3DP GC electrodes avoids the use of adhesives,and promotes the electron transmission between catalysts and the conductive carrier,as well as the rapid and effective contact with the ions in the electrolyte.(?)The 3DP GC electrodes break through the limitation that traditional electrodes cannot improve the performance by increasing the thickness and realizes efficient water splitting under the thick electrodes.In addition,3D printed graphene/carbon nanotube electrodes can also be used in other fields of electrocatalysis and have great potential for improving catalytic performance.