Effect of Additives in the Stabilization of the α Phase of Ni(OH)[sub 2] Electrodes

Abstract

The present work deals with the voltammetric and electrogravimetric behavior of Ni͑OH͒ 2 electrodes in alkaline solutions and the effect of some additives, such as Co 2ϩ , Cd 2ϩ , and Zn 2ϩ , in the active material. The electrochemical behavior of the ␣ or ␤ phases with the incorporation of the additives is analyzed by use of the electrochemical quartz crystal microbalance. Only Zn 2ϩ as additive leads to the complete stabilization of the ␣ phase avoiding, since the first cycle, the insertion of alkaline cations from the electrolyte. In all other ␣ phases, the electroneutralization of charge is achieved by a small but representative participation of cations. In the case of ␤ electrodes, protons are the responsible for charge compensation, the cations movement being negligible.The use of additives in the active material of batteries in order to improve the performance of the electrodes is a widely used treatment. The performance of the electrodes may be limited by chemical problems related to the species participating in the electrode process or by the aging of the materials produced by repetitive charge/ discharge cycles, storage, and battery operation.Among the additives most used in alkaline batteries, we can enumerate carbon, Co͑OH͒ 2 , CuO, Co, CdO, Zn͑OH͒ 2 , Zn, and ZnO. 1 The effect of these additives is to improve electric conductivity of the active material and to give rigidity to the structure to minimize volume changes produced during cycling. Other additives act polarizing the oxygen evolution reaction, which is a parasite process that consumes the available capacity of the battery. 2 There are other kinds of additives, which are incorporated in the electrolyte, such as cellulose or LiOH. Moreover, during the preparation methods of electrodes, contamination with impurities present in the materials can occur, that would modify the electrochemical performance of the electrodes. These impurities are: organic compounds, anions like nitrate or metallic cations such as Tl ϩ , Fe 3ϩ , Mg 2ϩ , Ca 2ϩ , Al, or Si. 1 The purpose of the use of additives in the special case of Ni͑OH͒ 2 electrodes is to avoid three major problems: 3 ͑i͒ improve the charge efficiency by separating the redox couples O 2 /OH Ϫ and Ni͑II͒/Ni͑III͒, ͑ii͒ improve mechanical properties avoiding the socalled ␥ effect, and ͑iii͒ improve the electrical conductivity of the active material, specially, in the reduced state.It is well known that ␣-Ni͑OH͒ 2 is unstable in strong alkaline solutions and it transforms into ␤ form; so that, the expansion of the electrodes ͑␤/␤ transformation͒ and contraction ͑␣/␤ transformation͒ during charge/discharge cycling, will lead to the deterioration of the electrodes. This phenomenon is called the ␥ effect and is considered as detrimental for accumulators. Some metallic cations have been studied, and it was found that most of them improve some properties and worsen others. Cobalt and cadmium hydroxides are the most popular additives used in Ni͑OH͒ 2 electrodes. Cyclic voltammetry studies have shown that Co͑OH...

Study of the influence of the template concentration under homogeneous precepitation on the properties of Ni(OH)2 for supercapacitors

“…Usually, for the synthesis of ultrafine nickel hydroxide, the homogeneous precipitation is carried out at very high temperatures of 140-180 °С. Also, the microwave heating can be used for this purpose [26].…”

“…The second route can be realized by using surfactants [26] or template synthesis. Template synthesis is a synthesis of compounds in a template (matrix).…”

Template-assisted synthesis of Ni–Co bimetallic nanowires for urea electrocatalytic oxidation

“…2a) for NCNE, indicating the incorporation of cobalt in nickel catalysts can effectively decrease onset potentials of urea electro- oxidation. It has been reported that doping cobalt in nickel can increase the structural defects of nickel and thus provide more active sites for urea oxidation and decrease the reaction overpotential [11,[18][19][20]. In addition, the presence of cobalt allows nickel to achieve a higher oxidation state and inhibit water electrolysis, and thereby promoting the urea oxidation [10,21,22].…”

Eletrodos modificados por hidróxido de níquel: um estudo de revisão sobre suas propriedades estruturais e eletroquímicas visando suas aplicações em eletrocatálise, eletrocromismo e baterias secundárias

“…Na Tabela 1 estão sumarizados alguns dos trabalhos publicados envolvendo a utilização de aditivos nos eletrodos de hidróxido de níquel. [27][28][29][30][31][32][33] Sem dúvida, devido à sua importância, o estudo envolvendo a incorporação de aditivos à matriz do hidróxido de níquel é um assunto extremamente abrangente, com diferentes técnicas de caracterização e aplicações, independentemente da aplicação tecnológica do hidróxido de níquel e indispensável à utilização destes.…”