Preparation And Strain Effects Of Thin Films With CO₂ Electroreduciton Activity Or Oxygen Evolution Reaction Activity

CO₂ reduction（CER）and oxygen evolution reactions（OER）have aroused extensive attention due to their important role in the field of new energy.In recent years,"elastic strain engineering"has become one of the important means to improve the electrocatalytic reactivity of materials.Because elastic strain can change the electronic structure and surface adsorption strength of materials,so as to effectively regulate their CER and OER activities.However,the traditional methods of inducing elastic strain rely on the lattice mismatch between core-shell structure of nanoparticles or epitaxial nanofilms-substate system.And the elastic strain that can be imposed was small by this method.In addition,the elastic strain effect and the ligand effect exist simultaneously.It is difficult to study the mechanism of the elastic strain effect on the electrocatalytic activity of nanofilms individually,which limits the design and development of high-performance electrocatalytic materials.In order to study the sole elastic strain effect on the catalytic activity of materials,Cu films with CO₂ reduction activity and MnO_x films with OER activity were prepared on the NiTi substrate by electrodeposition.The NiTi shape memory alloy has a two-way shape memory effect and can successfully impose the relative larger elastic strain to thin films.The surface morphology of the film was characterized by SEM.The elastic strain of the film was analyzed by XRD.The products of CO₂ reduction were qualitatively and quantitatively analyzed by gas chromatography.Electrochemical analytical techniques including linear sweep voltammetry（LSV）and cyclic voltammetry（CV）together with chronoamperometric i-t curve were used for analyzing the strain effect on the CER activity of Cu film and the OER activity of MnO_x films.The strain engineered mechanism for the electrocatalytic activity modulation was also explored.The main conclusions include:（1）For CO₂ electrocatalytic reduction,the CER activity of Cu film was affected by the surface morphology of the film,the reduction reaction potential and the CO₂ flow rate.The optimal CER experimental parameters were:bias potential at-2.1V and CO₂ flow rate of 40 mL/min,formed copper nanowhiskers;（2）0.51%compressive strain and 0.28%tensile strain were successfully imposed to the Cu thin films,and the compressive strain was favorable for the formation of CH₄,and the tensile strain preferentially generated C₂H₄;（3）NiSO₄ or Ni（NO₃）₂ solution could dope Ni into MnO_x film successfully as the doping Ni solution,and the doping of Ni greatly improved the OER catalytic activity of the film;（4）The substrate surface of Ni-MnO_x film was dense and homogeneous.The composition of MnO_x wasα-Mn₂O₃ and MnO₂ and the corresponding OER potentials of 10mA/cm² current density were 1.799 V,1.815 V（vs.RHE）,respectively.（5）The OER catalytic activity of the MnO_x film was reduced by the effect of compressive strain and NiTi substrate.