Regulating The Charge And Spin Ordering Of Two-dimensional Solids For Electrocatalytic Water Splitting

Focusing on the restraining factors?reaction energy barrier,the number of active site and electrical conductivity?of non-noble metal catalysts and sticking to the essential structure-activity relationship between inorganic solid catalyst?surface,charge and spin nature?and catalytic performance properties,this dissertation originally developed an ingenious strategy by constructing defect-confined two-dimensional atomic nanosheets?including vacancy,distortion and doping?to synergistically modulate the above three restraining factors.In this dissertation,we emphasize the mechanism of defect for the improved electrocatalytic performance at atomic scale.Moreover,the original concept of coordinated regulation presented in this work can broaden horizons and provides new dimensions in the design of newly highly efficient catalysts.Details are listed as below:1.According to Yang Shao-Horn's principle,CoSe₂ has been identified as an efficient,affordable and sustainable alternative electrocatalyst for oxygen evolution reaction benefiting from its well-suitable electronic configuration of Co ions.However,the catalytic efficiency of pure CoSe₂ is still far below what is expected,which suffers from its poor active sites exposure yield.Herein,we successfully overcome the disadvantage of insufficient active sites in bulk CoSe₂ by reducing its thickness into atomic scale rather than any additional modification?such as doping,hybriding with graphene or noble metals?.The insights gained from Positron annihilation spectrometry,XAFS spectra,and first principle calculations provide clear evidence that the easily formed VCo" vacancies can serve as active sites to efficiently catalyze the oxygen evolution reaction,manifesting an OER overpotential as low as 0.32 V at a current density of 10 mA cm^-2 in pH 13 medium,which is superior to its bulk counterparts as well as the most reported Co-based electrocatalysts.Considering the outstanding performance of the simple,unmodified ultrathin CoSe₂ nanosheets as the only catalyst,further improvement of the catalytic activity is expected when various strategies of doping or hybriding are used.These results not only strongly suggest the promise of an efficient,robust,and economic OER electrocatalyst based on ultrathin CoSe₂ nanosheets,but also open up a promising avenue into the design of highly active and stable catalysts towards replacing noble metals for oxygen electrocatalysis.2.We successfully constructed atomically-thin Co₃S₄ nanosheets with Jahn-Teller distorted octahedral exclusively exposed,which is clearly confirmed by the high-angle annular dark field?HAADF?image.Even more importantly,the spin states of Co³⁺ in the exposed octahedral self-adapted from low spin to high spin states as the nanosheets configurations thinning atomically-thick.Benefiting from the synergistic effect of the atom structural and electronic configuration modulations,these atomically-thin Co₃S₄ nanosheets manifest an OER onset overpotential as low as 0.31 V and superlarge polarization current?3.97 mA cm^-2 large at the overpotential of 0.7 V at neutral pH,which the integrated performance outperforms most of pure spinel OER electrocatalysts even held the state-of-the-art record among the inorganic non-noble metal compounds.What's more,the success of simultaneous optimization exposed octahedral active planes and self-adapted spin states by innovative establishing atomically-thin nanosheets features in this work undoubtedly provide profound perspective in pursuing efficient electrocatalysts.3.The exploration of efficient nonprecious metal eletrocatalysis of the HERis an extraordinary challenge for future applications in sustainable energy conversion.The family of first-row-transition-metal dichalcogenides has received a small amount of research,including the active site and dynamics,relative to their extraordinary potential.In response,we developed a strategy to achieve synergistically active sites and dynamic regulation in first-rowtransition-metal dichalcogenides by the heterogeneous spin states incorporated in this work.Specifically,taking the metallic Mn-doped pyrite CoSe₂ as a self-adaptived,subtle atomic arrangement distortion to provide additional active edge sites for HER will occur in the CoSe₂ atomic layers with Mn incorporated into the primitive lattice.Synergistically,the DFT simulation results reveal that the Mn incorporation lowers the kinetic energy barrier by promoting H--H bond formation on two adjacently adsorbed H atoms,benefiting H₂ gas evolution.As a result,the Mn-doped CoSe₂ ultrathin nanosheets possess useful HER properties with a low overpotential of 174 mV,an unexpectedly small Tafel slope of 36 mV/dec,and a larger exchange current density of 68.3 ?H cm^-2.Moreover,the original concept of coordinated regulation presented in this work can broaden horizons and provide new dimensions in the design of newly highly efficient catalysts for hydrogen evolution.