Preparation And Performance For Hierarchical Structure Electrode Materials Based On Two-Dimensional Nanomaterials

Two-dimensional nanomaterials have aroused extensive attention in electrochemical field due to their unique layered structure,excellent physical and chemical properties.However,their restacking or aggregation during the electrode fabrication process has greatly hindered their further developments and applications in electrochemical field.Under this background,our studies mainly focus on the design and development of a series of hierarchical structures electrode materials based on two novel two-dimensional nanomaterials——Ti₃C₂T_x and MoS₂,and systematically exploring their potential practicability in electrochemical applications,including electrocatalytic oxygen evolution reaction(OER),electrocatalytic hydrogen evolution reaction(HER)and aqueous zinc-ion battery.The main conclusions are as follows:A strategy is developed to fabricate the hierarchical cobalt borate/Ti₃C₂T_x MXene(Co-B_i/Ti₃C₂T_x)hybrid through simple and fast chemical reactions at room temperature.This unique hierarchical structure of Co-B_i/Ti₃C₂T_x hybrid is beneficial for exposing more active sites,improving mass diffusion and charge-transfer pathways for electrochemical reaction.Moreover,a strong interaction between Co-B_i and Ti₃C₂T_xensures efficient charge transfer and facilitates the electrostatic attraction of more anionic intermediates for a fast redox process.Consequently,the hierarchical Co-B_i/Ti₃C₂T_x hybrid shows extraordinary OER catalytic activity to deliver a current density of 10 mA cm^–2 at an overpotential of 250 mV,and a low Tafel slope of 53 mV dec^–1.A unique method is designed to prepare the hierarchical“nanoroll”like MoS₂/Ti₃C₂T_x hybrid by combining liquid nitrogen-freezing and subsequent annealing.The quick freezing of the Ti₃C₂T_x nanosheets and ammonium tetrathiomolybdate mixture causes a sudden change in the strain of Ti₃C₂T_x,which leads to form a novel“nanoroll”like hierarchical structure.After annealing at H₂/Ar atmosphere,vertically aligned MoS₂ crystallites are in situ formed in and on the nanoroll like Ti₃C₂T_x.Notably,this hierarchical MoS₂/Ti₃C₂T_x hybrid exhibits excellent HER catalytic activity with a small onset overpotential of 30 mV,and a more than 25-fold increase in the exchange current density compared with MoS₂ was observed.The hierarchical“nanoflower”like MoS₂ with different phase contents was successfully prepared through a simple and effective controllable phase engineering.The study found that the obtained“nanoflower”like MoS₂ with different phase contents showed distinct performance when used as cathode materials for rechargeable aqueous zinc-ion battery.It's worth noting that the“nanoflower”like MoS₂ with high 1T phase content displays excellent specific capacity and shows outstanding cyclic stability.Besides,the mechanisms involved were systematically explored by not only comprehensive characterizations,but also the density functional theory(DFT)simulations.A hierarchical high-content 1T phase MoS₂ self-supported electrode was successfully prepared by a simple one-pot hydrothermal method.This unique hierarchical electrode structure can not only shorten the reaction pathways of ions and electrons,expose more active sites,but also significantly improve the stability of MoS₂.When this free-standing electrode was directly used as rechargeable aqueous zinc-ion cathode electrode,it exhibits outstanding capacity and stability.Even though after 1000and 2000 cycles at a high current density of 2000 mA g^–1,the capacity retention rates are still up to 97.2%and 87.8%,respectively.