Synthesis Of 2D Nanocomposites And Their Catalytic Performance In Water Splitting

With the fossil energy increasingly dried up and the human environment polluted gradually serious,exploiting clean and renewable energy is already in the extremely urgency.Water splitting may offer an economic and efficient solution to produce a sustainable and environmentally benign H2 fuel.This process will involve a series of reaction combined with the hydrogen evolution reaction（HER）in cathode and the oxygen evolution reaction（OER）in anode.Up to date,Pt-group metal and metal oxide,are acknowledged as the best catalysts for water splitting.However,their commercial use as water splitting catalysts is prohibited due to their expensive cost and scarcity.Therefore,a cost-effective alternative of HER/OER catalysts should be developed as an aim for the future of hydrogen economy.Two-dimensional（2D）nanomaterials have been paid much attention due to their rich reserves,large surface area and unique quality.In addition,further nanostructure engineering can make 2D nanomaterials full of active sites and surface defects.In this paper,2D nanomaterials with different morphologies and structures were synthesized and their catalytic properties were investigated.The main points are shown as follows:1.An ultrathin Co₃O₄ nanosheet is uniformly deposited on the chemical exfoliated MoS2 nanosheet（ex-MoS2）via an in-situ hydrolysis and epitaxial growth.These novel noble-metal-free OER catalysts were proposed as an excellent platform for water splitting to promote the oxygen evolution activity and stability.MoS2 introduction can improve the conductivity of Co₃O₄ nanosheets,generate more Co3+species in Co₃O₄ nanosheets during electrochemical activation and render high durability against dissolution of Co₃O₄ nanosheets in high potential polarization.As a result,these novel Co₃O₄/ex-MoS2 hybrids exhibit an excellent OER activity with a remarkable low Tafel slope（ca.36 mV dec-1）,and a substantially small overpotential（ca.290 mV required for 10 mA cm-2）.Their OER stability is also outstanding,with 95.2%OER activity retention for 10000 potential cyclings.2.Ultrathin molybdenum sulfide（MoSx）nanosheets were uniformly grown on multiwalled carbon nanotubes（MWCNTs）via a solvothermal process.These MoSx nanosheets possess high density of active sites,full of the basal MoSx edges and unsaturated S atoms,and their one-dimensional（1D）core-shell architecture facilitates electron transfer and charge transport,leading to a superior performance in HER.These caterpillar-like MoSx@MWCNT hybrids show a high HER capability in 0.5 M H2SO4 solution with a low overpotential of 102 mV vs standard hydrogen electrode（SHE）and a small Tafel slope of 35 mV dec-1 at 10 mA cm-2.Their HER activity presents no significant decay during potential polarization at 150 mV vs SHE for over 5h.3.Porous NiCo diselenide nanosheets array on carbon cloth（CC）is synthesized via ion exchange with a hydroxide precursor.This bind-free three-dimensional（3D）architecture possesses the huge specific surface area and facilitates ion transport and charge transfer,leading to a superior performance in water splitting as a bifunctional catalyst for both HER and OER.The as-prepared NiCo diselenide/CC composites show a high HER capability in 0.5 M H2SO4 solution with a Tafel slope as small as 31.6 mV dec-1.They offer a HER current of 10 mA cm-2 at a low overpotential of 108 mV.Their OER efficiency is also remarkable in 1 M KOH solution with a small Tafel slope of 42.3 mV dec-1 and a low overpotential of 258 mV at 10 mA cm-2.This 3D porous NiCo diselenide nanosheet array holds a promise as an attractive alternative to precious catalysts of water splitting with high activity and long-term stability.