Preparation And Performance Study Of NiFe-based Catalyst For Seawater Electrolysis

Producing hydrogen by water electrolysis serves as an important technology for transforming the intermittent renewable energy sources to chemical energy.Electrolysis of water generates hydrogen at the cathode but highly dependent on efficient and stable oxygen evolution reaction(OER)at the anode.Currently,purified fresh water is used as electrolytes.However,large-scale freshwater electrolysis would put a heavy strain on vital water resources.The use of seawater instead of fresh water for hydrogen production is highly advantageous because of its abundance in nature(96.5%of the world’s total water resources).While the major issues are the electrode corrosion caused by Cl-(～0.5 M),and which is likely to occur oxidation at the anode then forms the competition with the OER.Herein,in this paper,transition metal(Ni,Fe)based nanomaterials as the main research object,combined with some excellent conductive substrates as carriers,and a new preparation method is adopted to develop a multi-level nanostructured OER catalyst for seawater electrolysis.The specific research work is as follows:1.Powdered NiFe-LDH nanosheet precursor was synthesized by water/solvothermal method.Then through calcining and phosphating at high-temperature,powdered Ni1-xFexP nanosheet catalysts were obtained to drop coating on the glassy carbon electrode.It was found that the OER performance of Ni0.80Fe0.20P/GC in alkaline seawater(1 M KOH+0.5 M NaCl)electrolyte was the best.dropcoating catalysts on a cheap carbon clothcan obtain Ni0.80Fe0.20P/CC,and its stability can be as long as 120 h at a current density of 10 mA·cm-2.2.In order to further optimize the problems in the long-term use of the powdered NiFeP catalyst in the structure-effect electrode and the seawater electrolysis with high currents,high-conductivity nickel foam with three-dimensional structure was chose as the substrate to prepare self-supported Ni1-xFexP/NF nano-array structure electrodes.The NiFe-LDH/NF precursors were synthesized by hydrothermal method,and then the self-supported Ni1-xFexP/NF nanoarray catalyst was obtained by phosphating.The study found that in 1 M KOH+0.5 M NaCl electrolyte,Ni0.75Fe0.25P/NF only needed 240 mV and 250 mV overpotentials at current densities of 200 mA·cm-2 and 500 mA·cm-2.The catalyst activity could last for more than 120 h.The in-situ reaction Raman characterization test showed that the continuously generating NiOOH and FeOOH on the surface of the material during the ORE process would resist the entry of Cl-in the seawater to corrode the catalyst,providing a new method for seawater electrolysis.3.On the basis of the continuous hydrothermal preparation of NiFe-LDH/NF,it was found for the first time that a self-supported S-NiFe-LDH/NF electrode catalyst could be prepared by low temperature sulfurization etching with Na2S solution.When the concentration of Na2S solution was 0.06 Mwith the temperature of 60℃ and the time of 120 min,the sulfur anion was inserted into the layered double hydroxide,which avoided the production of brittle metal sulfide.Besides,sulfide anion and hydroxide coexist,promoting the OER of seawater electrolysis.When it was 100 mA·cm-2 and 500 mA·cm-2 in 1 M KOH+0.5 M NaCl electrolyte,only 232 mV and 279 mV low potentials were required,respectively.After a stability test for up to 250 h,the voltage remained.And self-supported electrode still owned structure that maintained its own activity.At the same time,in the process of OER,the sulfur anion underwent oxidation reactions to produce sulfate ions,which could resist the corrosion of electrode materials by Cl-in seawater.It was simple and easy to operate without high temperature,high pressure and binderswith this method.And it could directly carry out large-scale seawater electrolysis to convert seawater into usable energy.