Construction Of High Efficiency Catalyst For Water Splitting Based On Metal Cobalt Organic Frameworks Derivatives

With the growth of global population,human demand for energy is increasing.At present,the vast majority of energy sources come from fossil fuels such as coal,oil and natural gas.However,fossil fuels belong to non-renewable energy sources,and they also produce by-products harmful to the environment in the combustion process.Solar energy,wind energy and hydrogen energy belong to sustainable and clean energy.Among them,hydrogen energy is the future energy that human beings dream of with the properties of non-toxic,harmless,high burning calorific value and non-pollution of combustion products.Obtaining hydrogen from electrolytic water is a green,simple and sustainable development technology.At present,the main commercial electrocatalysts for hydrolysis are platinum-based electrocatalysts for hydrogen evolution reaction?HER?,like platinum carbon electrocatalyst?Pt/C?,and ruthenium/iridium-based electrocatalysts for oxygen evolution reaction?OER?,like ruthenium dioxide?RuO₂?/iridium dioxide?IrO₂?electrocatalysts.However,the electrocatalytic stability of these materials is poor,and the content of precious metals is high,which leads to high prices and can not be widely used.Therefore,there is an urgent need to find alternative materials with low cost and high stability.In this study,two relatively inexpensive metal-organic frameworks?MOF?-derived hydrolysis electrocatalysts were developed by optimizing and modifying MOF.The main research contents are as follows.?1?Based on the controllable synthesis strategy of MOF materials,a small number of Pd nanoclusters were embedded in MOF-derived cobalt single atoms?Co SAs?carbon-nitrogen nanocages to synthesize Pd@Co SAs with super high hydrogen evolution electrocatalytic activity.Benefit from the strong adsorption capacity of metal Pd for hydrogen and the cubic porous structure of Co SAs carbon-nitrogen nanocages,Pd@Co SAs catalyst possess excellent electrocatalyactivity and stability at all pH values.When the current density is 10 mA cm^-2,its hydrogen evolution overpotential is 10 mV in 0.5 M H₂SO₄,8 mV in 1.0 M KOH and 53 mV in 1.0 M PBS.Its overall performance is superior to that of commercial platinum carbon?Pt/C?catalyst.In addition,the relative content of Pd in Pd@Co SAs is only 3.09%,which is much lower than that Pt?20%?in commercial Pt/C,indicating that Pd@Co SAs is a relatively inexpensive and highly active hydrogen evolution electrocatalyst.?2?Bifunctional Co-NC@Mo₂C composite electrocatalysts were prepared using ZIF-67 as precursor.Unlike traditional carbon packaging functional materials,nitrogen-doped carbon-coated cobalt nanoparticles?Co-NC?derived from ZIF-67 are encapsulated by Mo₂C.Benefit from the unique reverse-encapsulation structure and synergetic effects of Mo₂C and Co-NC,the Co-NC@Mo₂C catalyst shows superior hydrogen evolution reaction and oxygen evolution reaction performance.In alkaline media,it affords the current density of 10 mA cm^-2 at low overpotentials of 99 mV and 347 mV for hydrogen evolution reaction and oxygen evolution reaction performance,respectively.Interestingly,due to a reverse encapsulation structure where Co NPs are protected by Mo₂C,it leads to an outstanding HER electrocatalytic activity?a low overpotential of 143 mV?and stability in acidic solutions.Remarkably,when employed as both the cathode and anode for overall water splitting,a low cell voltage of 1.685 V is required to reach the current density of 10 mA cm^-2 in alkaline media with excellent stability,making the Co-NC@Mo₂C an efficient non noble metal bifunctional electrocatalyst toward water splitting.