본 연구에서는 리튬이온커패시터의 음극으로 polyaniline (PANI)/WO3 전극을 제조하고, 이의 전기화학적 특성을 측정, 분석하였다. WO3 전극 표면에 PANI를 전기화학적으로 담지 하였을 때 PANI의 용량이 더해져 WO3 전극보다 충, 방전 용량이 향상되었다. 한편, 충, 방전 시 태양광을 조사하여 충, 방전 용량과 쿨롱 효율(coulombic efficiency)에 빛조사가 미치는 영향을 파악하였다. WO3 전극과 PANI/WO3 전극에 태양광을 조사하였을 때, 두 전극의 충, 방전 용량과 쿨롱 효율은 태양광을 조사하지 않았을 때보다 증가하였다. 이는 WO3가 빛 조사에 의해 광전자를 생성하여 전극의 전기화학적 특성에 영향을 주기 때문으로 해석되며, PANI/WO3의 경우 PANI 또한 빛에 의해 여기 될 수 있어 전극의 특성이 변하게 된다. 빛 조사에 의해 추가로 생성된 광전자가 Li+ 이온의 삽입(intercalation)에 사용되어 용량을 증가시킬 수 있을 뿐 아니라, 전극의 전도성을 높여 쿨롱 효율을 향상 시키는 것으로 여겨진다. PANI/WO3는 충, 방전을 반복하여 진행하게 되면 PANI의 불안정성으로 인해 용량이 점차 감소되게 되지만, 빛 조사 시에는 생성된 광전자와 정공으로 인한 산화-환원 반응에 의해 PANI의 안정성이 크게 향상되어 충, 방전 용량의 감소없이 안정적으로 유지되었다.

In this study, polyaniline (PANI)/WO3 electrode was prepared as an anode of a lithium ion capacitor, and its electrochemical characteristics were measured and analyzed. When PANI was electrochemically deposited on the surface of WO3 electrode, the capacity of PANI/WO3 was improved with increase of the deposited amounts of PANI. Furthermore, the effect of light irradiation on capacity and coulombic efficiency was examined by irradiating sunlight during charging and discharging. When the light was irradiated to the WO3 electrode and the PANI/WO3 electrode, those capacities and coulombic efficiencies were increased compared to that measured under the dark condition. It is attributed to the photocatalytic property of WO3 that can generate photoelectrons by light irradiation. In PANI/WO3 electrode, PANI also can be excited under the light irradiation with affecting the electrochemical property of electrode. The photoelectrons improve the capacity by participating in the intercalation of Li+ ions, and also improve the coulombic efficiency by facilitating electrons’ transport. Under the dark condition, the capacity of PANI/WO3 was gradually reduced with increase of cycles due to a poor stability of PANI. However, the stability of PANI was significantly improved by the light irradiation, which is attributed to the oxidation-reduction reaction originated from the photogenerated electrons and holes in PANI/WO3.

Polyanilne WO3 Lithium ion capacitor Solar light

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