In-situ Measurement Of The PH Change At Cathode/Solution Interface And Its Effects On The Composition Of Electrodeposits

In recent years, most documents touched on the rechargeable batteries because the necessity of overcoming the shortage of energy sources and the pollution of our environment has become more and more important. The reported composite materials of Nickel hydroxides have been shown effectively to have the capability to enhance battery capacity and power abilities of rechargeable alkaline batteries. This can be validated by the investigations of Ni-MH, Ni-Cd, Ni-Zn, Ni-Fe batteries. In addition, the compound, structure and topography of the nanostructure materials have extensive effects on the properties of nickel hydroxide. In principle, many methods capable of producing the nickel hydroxide have been reported. The cathodic electrochemical deposition was usually employed to synthesize nickel hydroxide because it has much advantage, such as, good homogeneity due to the atomic-level mixing of solution-phase precursors, good film structure.However, nanostructure nickel hydroxide made by electrochemical deposition is usually focused on improvement of the electrochemical parameters, such as deposition time, solution composition, current density and after-treatment technology. But the research with the electrode/solution interface microcosmic chemical environment and mechanism of electrodeposition is limited and we will concentrate on these in this work.In this work, two pH-microsensor systems were designed for in-situ measuring the pH change at the substrate/solution interface during the electrochemical deposition process. There are two kinds of method to design the pH system to in-situ measureing the pH change at of the substrate/solution interface of electrochemical codeposition.The one kind was a novel pH system which employed a flat pH electrode (type E-901) to monitor the pH change. This flat pH electrode was covered with a stainless steel mesh of 300 meshes per square inch. The other kind was compound micro pH electrode which was including a platinum filament and a silver filament. The platinum filament was coated by poly-o-phenylenediamine (PoPD) in acid media in the presence of triethanolamine (TEA).The silver filament which was coated by a Ag/AgCl layer and was used as the reference electrode.The two kinds of pH electrode showed a Nernstion response with a slope of 66.7mV/pH and 59.8 mV/pH at the room temperature, and linear responses within the pH range of 2～13and 5～11, respectively. The correlation coefficients R were up to 0.99. The flat pH electrode was more stability and reproducibility and faster of the potential response than the PoPD-modified pH microelectrode.The above equipment was used for in-situ measuring the pH change at the substrate/solution interface during the electrodeposition process of Ni (OH) 2 in 0.01 mol·L-1 Ni(NO3)2 electrolyte of the pH at 2.5,3.54.5 and 5.5. The results indicated that the lower of pH value of substrate/solution interface and higher current density of electrode, with the lower of pH of the electrolyte. The above equipment was used for in-situ measuring the pH change at the substrate/solution interface during the electrodeposition process of Ni (OH) 2 in 0.01 mol·L-1 Ni(NO3)2 electrolyte at the voltage of -1.00,-1.02,-1.04 and -1.06 V. The amounts of electrodeposited Ni (OH)2 were determined by inductively coupled plasma-atomic emission-spectrometry (ICP-AES) after dissolution of the compound. The results indicated that Electrodeposition Efficiency of Ni (OH) 2 has a functional relationship with pH values of substrate/solution interface in the electrochemical deposition process. In addition, the experimental results have a good agreement with the mathematical model by thermodynamic analysis.A series of nickel-cerium hydroxide compounds were prepared from aqueous solutions containing Ni (NO3)2 and Ce (NO3)3 by the potentiostatic technique using a three-electrode system. The pH changes at the cathode/solution interface were in-situ measured by the novel equipment during the electrodeposition process of mixed erbium-zinc hydroxide or oxide compounds. The solution- and solid-phase speciation distributions of the two metal ions and their hydroxides as a function of pH values, which were calculated and plotted according to the thermodynamic constants for these species, were used to explain the reaction mechanism for electrocodeposition of mixed nickel-cerium hydroxides on cathodic surfaces and predict the composition for the mixed nickel-cerium hydroxides compounds.