Cobalt-based Nanosheet Array Electro-catalysts For Overall Water Splitting

Energy crisis and environmental pollution greatly threatened the sustainable development of human society,only the development of a clean,renewable,safe and efficient new energy can solve this problems.Hydrogen have advantages of clean,high efficiency,storable,cheap and easy to get,is an ideal,the most potential for the development of secondary energy.In several methods of preparing hydrogen,electrolysis of water is the most promising for large-scale application of hydrogen technology in future,therefore,the design and development of a high catalytic activity,high stability of electrocatalyst for water splitting,is the key step of this clean energy to commercial applications,to solve the energy crisis and environmental pollution problems.The noble metal represented by platinum is a high performance electrolytic water catalyst,but the precious metal are scarce and expensive,which directly restricts its application.Therefore,it is necessary to study electrocatalyst for water splitting based on non-precious metal materials.Transition metal cobalt is rich in source,low in price,its simple substance and compounds with good electrochemical catalytic performance,is expected to replace the precious metal catalyst.In this paper,we have prepared a cobalt-based electrochemical catalyst with a nanosheet array structure for the catalytic electrolysis of water by a simple and easy electrochemical deposition method,which activity is higher and the stability is better than noble metal catalyst represented by platinum and iridium oxide.The main research contents are as follows:1.The porous Co0.85Se precursor was prepared by a simple electrochemical deposition method,and then make anodic or cathodic reactions in 1 M KOH solution,respectively.In this process,Se in the precursor was "sacrificed",the Co0.85Se precursor was converted into Co3O4 ultrathin-nanosheet arrays(Co3O4 UNA)and Co(OH)2 ultrathin-nanosheet arrays(Co(OH)2 UNA).The thickness of Co3O4 UNA is only 1.20 nm,and Co(OH)2 UNA is 1.40 nm.Co3O4 UNA and Co(OH)2 UNA have advantages of large electrochemical active area,good electrical conductivity and outstanding permeability compared with other electrocatalyst for water splitting.We made an electrolytic cell using Co3O4 UNA and Co(OH)2 UNA as anode and cathode,respectively.In alkaline media,the Co3O4 UNA 1 Co(OH)2 UNA electrolyzer reached 10 and 50 mA·cm-2 at a voltage of 1.41 and 1.69 V,respectively.In 1 M neutral phosphate buffer media,the Co3O4 UNA 1 Co(OH)2 UNA electrolyzer reached 10 and 50 mA·cm-2 at a voltage of 1.80 and 2.03 V,respectively.In addition,the electrolytic cell are tested in a large current density for 10 hours continuous electrolysis,the performance did not occur attenuation.These data show that the electrolytic cell composed of Co3O4 UNA and Co(OH)2 UNA is superior to the electrolytic cell composed of iridium dioxide and platinum as the anode and cathode,respectively,on the activity and stability.At the same time,the morphology,structure and composition of Co0.85Se precursor,Co3O4 UNA and Co(OH)2 UNA were characterized by SEM,TEM,XRD,XPS,BET,AFM and ICP.The effects of the structure and morphology of the two catalysts on the catalytic performance were analyzed.2.Co-Ni-Fe-Se composite OER catalyst and Co-Ni-Fe-Se composite HER catalyst were prepared by electrochemical deposition method respectively.Both catalysts have a nanosheet array structure with excellent OER,HER activity and stability in KOH solution.The two nanosheet array catalyst was assembled into an electrolytic cell for electrolysis of water.When 1 M KOH was used as the electrolyte,the electrolytic cell reached 50 mA·cm-2 at a voltage of 1.61 V.The voltage of electrolytic cell was basically maintained at 1.76 V for 150 hours water splitting test at a current density of 120 mA cm-2,indicating that the catalyst has high activity and excellent stability.The morphology,structure and composition of the catalysts were characterized by SEM,TEM,XRD,XPS,BET,ICP and so on.The effects of the structure and morphology of the catalysts on the catalytic performance were analyzed.