Transition Metal Based Porous Ultrathin Two-Dimensional (2D) Nanosheets: Synthesis And Electrocatalytic Reduction Reaction Performances

Developing highly active and low-cost electrocatalysts is the key factor to achieve efficient electrocatalytic reduction.At present,transition metal based catalysts have showed excellent electrocatalytic performance,but the low atomic utilization of them will decrease the mass activity for practical use.Porous ultrathin two-dimensional(2D)nanomaterials with several nanometer-sized thickness are expected to solve above-mentioned problems well by virtue of ultrahigh specific surface area,abundent active sites and fast electron/carrier transfer rate.The exposed facet of catalysts has a great influence on the activity.Vacancy and heterostructure can also optimize the electronic structure and improve the performance.However,it is still a great challenge to synthesize porous ultrathin two-dimensional materials combined with facet effect,vacancy and heterostructure.Herein,a series of solid material chemical conversion methods have been developed in this work to synthesize porous ultrathin two-dimensional nanosheets regulated by crystal facet,vacancy and heterogeneous structure.The electrocatalysts prepared by these methods have shown high mass activity for hydrogen evolution from water-splitting and high selectivity and yield for transfer hydrogenation.The main study contents are summarized as below:1.A convenient solid gas chemical transformation approach was developed to synthesize porous ultrathin CoP nanosheets(denoted as CoP UPNSs)with a high proportion of exposed active facet and high mass activity for efficient HER in acid solution.The CoP UPNSs are highly efficient for HER with the huge mass activity of151 Ag^-1 at the overpotential of 100 m V and the mass activity is over 80 times higher than that of CoP NPs.Importantly,other metal selenide and sulifide ultrathin porous nanosheets(e.g.CoSe₂,CoS)with a specific exposed crystal surface can be achieved by using this chemical transformation strategy.Our generalized strategy may open a powerful route to synthesize porous ultrathin 2D materials that can't be prepared using the other reported methods.Furthermore,the work also did some exploration in improving the electrocatalytic performance through porous ultrathin two-dimensional structure and crystal surface engineering.2.A facile plasma-induced dry exfoliation strategy was developed to prepare non-layer structured Co₃S₄ ultrathin porous nanosheets with sulfur vacancies(denoted as Co₃S₄ PNS_vac)with high mass activity for efficient alkaline HER.Co₃S₄ PNS_vacpossess an extremely large mass activity of 1056.6 Ag^-1 at an overpotential of 200 m V,which is over 107 times higher than the value of Co₃S₄ NP.Interestingly,other nonlayered structured transition metal-based alkaline HER electrocatalysts(e.g.,CoSe₂,NiSe₂)with ultrathin,porous and vacancy-rich structure can also be prepared through this plasma-induced dry exfoliation strategy.Our findings could not only prepare nonlayered structured ultrathin porous nanosheets with sufficient vacancies which are difficult to obtain by other methods,but also provide a new way to regulate the electrocatalytic properties of two-dimensional nanomaterials through defect and porous ultrathin structure engineering.3.A facile convenient solid gas chemical transformation method to synthesize heterostructure MoNi₄/MoO₂ porous ultrathin nanosheets(denoted as MoNi₄/MoO₂PNS)for efficient electrochemical transfer hydrogenation reaction.We chose porous ultrathin NiMoO₄ nanosheets as the precursor and Mo Ni₄ nanoparticles were in situ grown on porous ultrathin MoO₂ nanosheets by gas solid reaction.The heterostructure electrocatalyst could convert nitroarenes into high value-added azoxy aromatic compounds with nearly 100%selectivity and efficiency through reduction reaction in gram-scale.Our study could not only offer a new perspective for electrochemical transfer hydrogenation reaction,but also provide a novel approach to control the electrochemical transfer hydrogenation performance of two-dimensional nanomaterials through heterostrcuture and ultrathin porous structure engineering.