Study Of Electrodeposition,Treatment And Catalytic Oxygen Evolution Of Nickel-Copper-Iron Alloys

The development of human society has a growing demand for new energy.Water electrolysis is an important electrochemical reaction in the field of new energy and environment.Oxygen evolution reaction?OER?,as a slower semi-reaction,requires an efficient catalyst to accelerate this slow kinetic process of water oxidation.Reducing the overpotential of the oxygen evolution reaction process and developing a high-performance non-noble metal oxygen evolution catalyst have become an urgent problem to be solved.In this thesis,nickel-copper-iron ternary alloys are prepared by using bipolar gradient electrodeposition and selective ion stripping.The electrochemical performance of the alloys is evaluated as an OER electrocatalyst.The Ni-Cu-Fe alloys with gradient composition and microstructure weresuccessfully prepared on nickel substrates by bipolar electrodeposition method.This technology is based on the potential gradient between the interface of bipolar electrode?BPE?and electrolytic solution.The gradient of interface potential makes the electrodeposition rate of different metal atoms change along the length of BPE,so that alloys with gradient composition can be prepared.Field emission scanning electron microscope?FESEM?was used to characterize the surface morphology of the electrodeposits,and energy dispersive X-ray spectrometer?EDS?was used to determine the chemical composition of the alloys.The analysis results show a gradient distribution in both size and composition.The obtained gradient alloys were tested as an OER electrocatalyst.The local OER activity of the gradient alloy was assessed in 1.0 M KOH using area-step cyclic voltammetry?ASCV?,without the need of splitting the BPE into separate partitions.This new approach is based on an idea of exactly controlling the contact area between the electrolyte and the electrode surface.The feasibility of the ASCV method was proved by parallel experiments.The parallel experiments consistently point to the same position on the gradient surface where presents the highest intrinsic OER activity.The surface roughness gradient can also be characterized using the same method.The experimental results show that the Fe content and surface roughness in Ni-Cu-Fe alloys play an important role in OER.Using conventional constant potential deposition techniques,the Ni-Cu-Fe alloys were prepared as master alloys by co-deposition in a mixed solution containing three metal ions of nickel,copper,and iron.According to the voltammetric curves of the parent alloys in 4.0 M NaOH,Cu was selectively etched for dealloying.The Ni-Cu-Fe electrode after the selective ion stripping exhibits a significantly increased activity to the water oxidation in alkaline medium.The Ni-Cu-Fe alloy obtained under the optimal stripping conditions can reach a very low overpotential of 213 m V for the OER at a current density of 10 m A cm^-2.On the above basis,iron was introduced onto the surface of Ni-Cu alloys in another way.The binary alloys only containing Ni and Cu were prepared as the parent alloy by using the constant potential method.Then the selective Cu stripping was performed in 4.0 M NaOH containing a certain amount of iron salt to obtain Ni-Cu-Fe ternary alloys.The alloys prepared in this way show a higher OER activity.The overpotential is only 199 m V at a current density of 10 m A cm^-2.FESEM and field emission transmission electron microscopy?FETEM?were used to observe the changes of electrode deposits before and after modification by selective ion stripping,and energy dispersive EDS was used to determine the changes in alloy chemical composition.It is proved that the non?noble metal alloy prepared by the selective ion stripping method exhibits significant activity on water oxidation in alkaline medium.In summary,the non-precious metal Ni-Cu-Fe alloys can be used as a very promising catalyst for oxygen evolution reaction,and it can replace the precious metal catalysts such as ruthenium and iridium to a certain extent,thereby reducing the catalyst cost for the hydrogen production from electrolyzed water.