The preparation of partially substitutional AB2 hydrogen storage alloy and the effect of the alloy modification by electroless nickel coating on the electrochemical performance of electrode

• Main Authors: Jenq; Shiang Ning, 鄭湘寧
• Other Authors: C. C. Wan; Y. Y..Wang
• Format: Others
• Language: en_US
• Published: 1995
• Online Access: http://ndltd.ncl.edu.tw/handle/65791486919523948406

碩士 === 國立清華大學 === 化學工程研究所 === 83 === AB2型Laves phase合金具有優異的儲氫量及吸氫速率等特性，適合作為鎳 氫二次電池的負極材料。本實驗將實驗計劃法得到的 Ti0.35Zr0.65Ni0.6 V1.4 以Mn置換部分V並適當調整比例，希望找到具單純結構和優異電容量 的合金組成，藉無電鍍鎳表面處理改善合金抗腐蝕能力及提高合金高速放 電容量，並探討無電鍍鎳對電極電化學性質的影響。從合金性質的實驗結 果的分析，我們發現添加Mn有助於合金結構的純化，使合金具有C14型式 六方(hexagonal)結構。將Ni化學計量提高至1.0和1.2，Mn化學計量定 為0.2和0.4，我們找到較佳的負極材料Ti0.35Zr0.65Ni1.2Mn0.2V0.6 其 放電容量在310mAh/g附近，放電時電壓保持平穩，並且合金具有相當優異 的放氫能力。經由表面無電鍍鎳處理後合金會保有高電容量的原有特性， 且具有優異的高速放電能力及抗腐蝕能力。鎳鍍層良好抗腐蝕能力能有效 增長電池循環壽命並且在過放電期間提供良好防護能力使電極免於過度氧 化所造成的電容量損失。此外，我們發現電極高速放電能力與電極表面催 化活性有關：電極催化活性（交換電流值）愈高，其高速放電能力愈佳。 相對於 Ni-P鍍層而言，純Ni鍍層能提供電極較佳的催化活性。但合金粉 末在純Ni電鍍期間，由於在鹼性環境中合金活性表面產生氧化層，造成電 極需要相當長的活化過程。而Ni-P鍍層合金所需活化次數較少，但其高速 放電能力較純Ni鍍層合金差。在合金粉末上先施以Ni-P表面無電鍍處理再 鍍上純Ni鍍層能兼具兩種鍍層之長而互補其短；即保有純Ni鍍層合金優異 的高速放電能力和具有Ni-P鍍層合金快速的的活化能力。 The P-C-T curves and electrochemical properties of Laves phase (AB2) hydrogen storage alloy based on Ti0.35Zr0.65Ni0.6V1.4 alloy by partial substitution or addition with Mn were examined. Besides, the electrochemical performances of AB2- type hydrogen storage alloy (Ti0.35Zr0.65Ni1.2V0.6Mn0.2) modified by electroless Ni-P and Ni coatings in acid hypophosphite and hydrazine baths, respectively, have been investigated . It was found that the addition of Mn into the original alloy contributed toward the uniformity of alloy exhibiting a C14 hexagonal structure. Based on the experimental results, the composition Ti0.35Zr0.65Ni1.2V0.6 Mn0.2 with large hydrogen storage and good reversibility for hydrogen desorption is recommended. We also found that electrochemical properties of the modified electrodes including high rate dischargeability, cycle life, retaining ability for discharge capacity during overdischarge, and electrocatalytic activity for hydrogen electrode reaction were improved by surface modification. The high rate dischargeability of the alloy coated with Ni in the hydrazine bath was better than that coated with Ni-P in the acid hypophosphite bath, but the activation cycles needed for reaching maximum capacity of the Ni coated electrode were four times as long as those coated with Ni-P. A compound nickel coating method was therefore developed. The compound nickel coated alloy ( i.e., alloy first coated with Ni-P and then with Ni ) retained the characteristics of better high rate dischargeability but needed fewer activation cycles when compared with Ni coated alloy.