銅與SS304不銹鋼基材電鍍披覆Cr-C後在釩電池正極電解液中之腐蝕行為

Corrosion Behavior of the Cr-C Coatings Electroplated on Copper and SS304 Substrates in the Solution of Positive-electrode Compartment of Vanadium Redox Flow Battery (VRFB)

本論文在探討銅與不銹鋼基材上經無毒三價鉻鍍浴電鍍Cr-C披覆後，浸泡於釩電池正極電解液中（2.04 M H2SO4 + 2.0 M VOSO4）之電化學法腐蝕行為，藉以評估其作為釩電池雙極板可行性。研究結果顯示：基材種類與電鍍條件對於Cr-C披覆層之表面形貌造成影響，在低電流密度（6 A/dm2）下，銅基材鍍層不會顯示裂痕，但在高電流密度（18 A/dm2）下兩種基材上所得鍍層表面皆出現裂痕，裂痕數量與密度隨電鍍時之電流密度之增高而增加。披覆層之成分經電子微探儀（EPMA）分析顯示：電鍍電流密度上升時所得披覆層之含碳量減少，X光電子成分分析儀（XPS）測得高含碳量之鍍層Cr-C含量也高。陽極動態極化法（APDP ）評估銅與不銹鋼兩種基材上Cr-C鍍層在模擬釩電池正極電解液中之腐蝕行為，顯示不銹鋼在電鍍電流密度10 A/dm2下電鍍10分鐘所得鍍層之腐蝕速率最低。另以電化學阻抗頻譜（EIS）偵測在此模擬溶液中施加1.0 VSCE（釩電池之理論充電電位）之阻抗，結果顯示在經電流密度為10 A/dm2下電鍍不銹鋼10分鐘後所得之鍍層，擁有最大之阻抗半圓（6600Ω），耐蝕性最佳。相對而言，為基材電鍍Cr-C披覆層之耐蝕能力較差，其在釩電池正極電解液中的耐蝕能力不如不銹鋼的Cr-C披覆。

Cr-C coatings were carried out electrochemically by means of non-toxic trivalent chromium bath on both copper and SS304 to evaluate their availability as bipolar plates in the vanadium redox flow battery (VRFB). In this work, the coatings were immersed in a simulated solution (i.e., 2.04 M H2SO4 + 2.0 M VOSO4) of the positive-electrode compartment in VRFB to evaluate their corrosion behavior. Examination through (SEM) indicated that the surface morphology of the coatings depended upon the substrate and current density of the electrochemical deposition. No obvious cracks could be observed in the coating of copper substrate electrochemically deposited at lower current density (6 A/dm2); however, cracks were distributed apparently in the coating of both substrates. The size of cracks and their distribution density on the surface were determined by the current density in the electrochemical deposition. Crack size and distribution density of the cracks increased with increasing the current density (18 A/dm2) of the electrodeposition. Analysis through EPMA demonstrated that the carbon content in the coatings increased with the current density in the electroplating process. XPS result revealed that Cr-C composition was proportional to the C-content. Anodically, potentiodynamic polarization (APDP) was conducted in the simulated positive-electrode solution to estimate different Cr-C coatings indicated that Cr-C coating on SS304 resultant from electroplating at 10 A/dm2 for 10 minutes was more corrosionresistant than that on copper. Electrochemical impedance spectroscopy (EIS) showed that that the coating on SS304 (electroplated at 10 A/dm2 for 10 minutes) revealed the highest corrosion impedance (6600 Ω) while it acted as the electrode charged at 1.0 V(i.e., theoretical charging voltage of the VRFB ) in the simulated solution. The corrosion behavior of the coating on SS 304 is similar to that of graphite electrode currently used. In contrast, the Cr-C coatings on copper were inferior to those on SS304 with respect to the corrosion resistance.