| Electrocatalytic water splitting,coupled with renewable energy power generation systems represented by photovoltaic and wind energy,can provide ideal technical means for future sustainable hydrogen energy supply.Water splitting reaction can be divided into two half reactions,hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).However,OER involves a slow kinetic four-electron transfer process and is regarded as a bottleneck reaction in water electrolysis.At present,alkaline electrolyzers are the most mature commercial water electrolysis technology.Due to the inherent low catalytic activity,the use of nickel as an anode electrode severely limits the efficiency of water electrolysis.Development of stable and highly active nickel-based OER electrodes is of great significance for the effective use of hydrogen and renewable energy in the perspective of hydrogen economic strategy.To improve the catalytic activity of the nickel electrode,a variety of high-performance nickel-based materials were prepared as alkaline water oxidation electrodes via boronization,electrochemical oxidation,rapid ion exchange surface modification strategies.We clarified the structure-activity relationship between the surface structure and activity of nickel electrode materials,revealed the true catalytically active phase in the catalytic process,and realized the extreme value of the intrinsic catalytic activity of the OER catalysts.The main research contents are as follows:1 We convert the nickel plate into a boronized Ni electrode via boronization method with amorphous boron powder.It is revealed that boronization improves the intrinsic catalytic activity of the nickel electrode.We describe the activation of boronized nickel sheets during the electrochemical OER test.Nanosheets were generated in situ on the electrode surface,and metaborate containing?-Ni OOH was found to be the main catalytic active phase in the catalytic process.The activated boronized Ni exhibited a catalytic activity nearly ten times higher than that of the pristine Ni,and maintained significant catalytic stability for more than 1500 hours.The enhanced catalytic performance of activated boronized Ni is attributable to the co-optimization of the thin nanosheet structure of hydrogen oxyhydroxide(ie,geometric optimization)and the modification of the electronic structure of the oxyhydroxides by metaborates(ie,electronic optimization).2 The realization of saline water electrolysis requires a stable,selective and high-performance OER catalytic electrode that can resist chloride ions.We prepared a multilayer oxygen-evolution electrode by two steps:(i)directly boronization of a commercially available Ni Fe alloy plate,(ii)electrochemical oxidation of boronized Ni Fe plate,to meet various needs of anode materials for saline water splitting.We pointed out that the electrode is composed of the surface oxidized Ni Fe B alloy layer as the catalytic active layer,the Ni Fe B alloy interlayer as the corrosion-proof layer and the Ni Fe alloy substrate as structural support.We reveal that the boron species in the oxidized Ni Fe Bx layer of the electrode surface layer exists in the form of metaborate.Corresponding experiments combined with theoretical calculation results prove that its existence contributes to the formation of the catalytically active phase?-(Ni,Fe)OOH during the catalytic reaction.At the same time,the intrinsic catalytic activity of the electrode material is improved by optimizing the electronic structure of the active phase.In addition,the stability results and corrosion behavior studies under the relevant chlorine-containing system confirmed that the Ni Fe Bx intermediate layer can effectively prevent the electrodes from excessive oxidation and corrosion in the chlorine-containing electrolyte.3 For industrial applications,achieving high OER current density with minimal overpotential and developing cost-effective high-performance OER electrodes are critical to improving the efficiency of electrolysis systems and achieving industrial hydrogen production.Square meters of surface-modified nickel mesh electrodes were rapidly realized via a cost-effective and industrially compatible method at room temperature and achieved current densities of 10 mA cm-2 and 100 mA cm-2 under an overpotential of 217 m V and 300 m V,respectively.This can electrode can be stable for more than 1900 hours.In the actual test of a commercial electrolyzer,the voltage required to reach a current density of 300 mA cm-2 is less than 2 V.The surface-modified nickel mesh electrode is expected to exert greater commercial value in practical industrial applications. |
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