Nanoporous Metal Compounds Supported Single-atom Catalysts And Their Water Electrolysis Application

Developing sustainable hydrogen energy technology is an important way to achieve the goal of carbon neutrality.Water electrolysis is one of the most promising hydrogen production approaches,which can convert water molecules into hydrogen using the electric energy generated by renewable and sustainable energy.The as-obtained hydrogen can be supplied as clean energy after storage.In the water electrolysis system,one of the core parts is the cathode and anode electrocatalysts,whose catalytic activities directly influence the efficiency of hydrogen production.Supported catalysts have been widely studied in the area of water splitting,which achieved high catalytic activity and low production cost by loading metal nanoparticles or nanoclusters on inexpensive substrate.The supported metal nanoparticles or nanoclusters exhibit different catalytic properties due to different size,morphology,and interaction with the substrate.However,only the surface atoms of supported metal nanoparticles or nanoclusters can catalyze the chemical reaction,leading to the low metal utilization.Reducing the size of nanoclusters to the level of atoms can achieve the ideal supported catalyst,namely,the single-atom catalysts.Single-atom catalysts are endowed with sharply increased surface free energy,quantum size effect,and unsaturated coordination environment,resulting in superior catalytic activity and selectivity.Moreover,the maximum metal utilization further reduces the production cost of single-atom catalysts.Although single-atom catalysts have prominent advantages,there are many challenges in the precise and large-scale preparation of high-loading single-atom catalysts.This work carried out the design and preparation of cathode and anode single-atom catalysts,optimized the electronic and atomic structure of single-atom sites to achieve highly efficient hydrogen production,and developed general synthetic method of high-loading single-atom catalysts.The main contents include the following four aspects:1.Single Pt atoms were embedded on the surface of nanoporous cobalt selenide through atomic-scale doping,leading to significantly improved catalytic activity for p H-universal hydrogen evolution reaction.The achieved catalysts exhibited high neutral hydrogen evolution reaction activity with a low overpotential of 55 m V,a low Tafel slope of 35 m V dec^-1,and a high Pt mass activity of 1.32 A mg^-1 at the overpotential of 100 m V,outperforming commercial Pt/C catalysts.In-situ X-ray absorption spectroscopy studies and density functional theory calculations revealed that the doping of single Pt atoms activates the neighbouring Co atoms into active sites for water adsorption and dissociation,thus facilitating the hydrogen evolution reaction kinetics.The enhancement mechanism of single Pt atoms doping opens up further opportunities for the design and preparation of efficient hydrogen evolution reaction catalysts.2.Engineering the electronic and coordinate structure of single atoms in single Ru atoms doped Mo S₂ catalysts via bending strain to achieve the improvement of alkaline hydrogen evolution reaction activity.The correlation between local strain and hydrogen evolution reaction activity was analyzed and discussed,which provides a pioneer method for modifying the electronic and atomic structure of single-atom catalysts.By using operando X-ray absorption spectroscopy and ambient pressure X-ray photoelectron spectroscopy techniques,it was clarified that the doping of single Ru atoms breaks the steric effect and allows the direct binding between Mo atoms and H₂O molecules,resulting in effective mass transfer of H₂O molecules to active Ru atoms.Significantly,the bending strain can accelerate water mass transfer and dissociation at the same time by tuning the electronic and atomic structure of catalysts.The as-obtained synergetic mechanism provides a new understanding for the active sites of single-atom catalysts.3.Nanoporous nickel-iron phosphides supported single Ir atoms were prepared by using a electrochemical deposition strategy.The single Ir atoms were stabilized in nickel-iron oxyhydroxides on the surface of nanoporous nickel-iron phosphides after surface self-reconstruction.The as-obtained catalysts exhibited excellent alkaline oxygen evolution reaction activity with a low overpotential of 197 m V and a low Tafel slope of 29.6 m V dec^-1.The Ir mass activity of our catalysts at the overpotential of 250 m V was calculated as 39.3 A mg^-1,which is131 times greater than that of commercial Ir O₂ catalysts.In situ X-ray absorption spectroscopy studies and density functional theory calculations identified the formation of dynamic active-sites and shrinkage structure on the surface of catalysts under reaction conditions,which is mainly responsible for excellent catalytic activity and stability.4.We developed a melt-quenching strategy for the large-scale preparation of high-loading single-atom catalysts.The combination of high-temperature melting and rapid-quenching enables the pinning of a larger number of noble-metal atoms in the metal compound phase of phase-separated alloy.The bicontinuous nanoporous morphology of metal compounds supported single-atom catalysts can be further fabricated by selectively chemical etching the metal phase.Guided by the phase diagram and standard electrode potentials,libraries of mono-or multimetallic single-atom catalysts can be synthesized by combining various supporting matrixes and single atoms.Considering the wide application of melt spinning system in metallurgy,the industrial production of single-atom catalysts based on melt-quenching strategy can be achieved by using the current industrial manufacturing platform.Besides,the single Ru atoms doped nanoporous Co₂P catalyst exhibited superior hydrazine oxidation reaction and hydrogen evolution reaction activities.Dramatically decreasing the input cell voltage of water electrolysis was realized by coupling the hydrazine oxidation reaction and hydrogen evolution reaction.