Korean Chemical Engineering Research

The Korean Institute of Chemical Engineers (한국화학공학회)
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Synthesis of Polyaniline/WO3 Anode for Lithium Ion Capacitor and Its Electrochemical Characteristics under Light Irradiation

리튬이온커패시터용 Polyaniline/WO3 음극 제조 및 이의 광 조사에 따른 전기화학적 특성 변화

  • Park, Yiseul (Department of Chemical Engineering, Pukyong National University)
  • 박이슬 (부경대학교 화학공학과)
  • Received : 2018.08.13
  • Accepted : 2018.09.17
  • Published : 2018.12.01
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Abstract

In this study, polyaniline $(PANI)/WO_3$ 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 $WO_3$ electrode, the capacity of $PANI/WO_3$ 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 $WO_3$ electrode and the $PANI/WO_3$ electrode, those capacities and coulombic efficiencies were increased compared to that measured under the dark condition. It is attributed to the photocatalytic property of $WO_3$ that can generate photoelectrons by light irradiation. In $PANI/WO_3$ 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 $PANI/WO_3$ 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 $PANI/WO_3$.

본 연구에서는 리튬이온커패시터의 음극으로 polyaniline $(PANI)/WO_3$ 전극을 제조하고, 이의 전기화학적 특성을 측정, 분석하였다. $WO_3$ 전극 표면에 PANI를 전기화학적으로 담지 하였을 때 PANI의 용량이 더해져 $WO_3$ 전극보다 충, 방전 용량이 향상되었다. 한편, 충, 방전 시 태양광을 조사하여 충, 방전 용량과 쿨롱 효율(coulombic efficiency)에 빛 조사가 미치는 영향을 파악하였다. $WO_3$ 전극과 $PANI/WO_3$ 전극에 태양광을 조사하였을 때, 두 전극의 충, 방전 용량과 쿨롱 효율은 태양광을 조사하지 않았을 때보다 증가하였다. 이는 $WO_3$가 빛 조사에 의해 광전자를 생성하여 전극의 전기화학적 특성에 영향을 주기 때문으로 해석되며, $PANI/WO_3$의 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. $PANI/WO_3$는 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.

Keywords

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Fig. 2. Cyclic voltammograms of PANI/WO3 prepared with different passed charge (Q) (0.5, 1, 1.5, 2, 3 mAh) for PANI deposition (a) at dark and (b) under light irradiation.

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Fig. 3. Specific capacitance of PANI/WO3 with different amounts of PANI under dark and light irradiation.

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Fig. 4. Cyclic voltammograms of WO3, PANI/FTO (Q = 1 mAh) and PANI/WO3 (Q = 1 mAh) (a) at dark and (b) under light irradiation.

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Fig. 5. Discharge/charge curves of WO3 and PANI/WO3 (Q = 1 mAh) electrodes at a current density of 0.35 A g-1 (a) at dark, (b) under light irradiation.

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Fig. 6. Cycle performance of WO3 and PANI/WO3 (Q = 1 mAh) electrodes at a current density of 0.35 A g-1 (a) at dark, (b) under light irradiation.

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Fig. 1. (a) SEM image of prepared WO3 electrode. (b) X-ray diffraction (XRD) patterns of PANI/WO3 (passed charge (Q) = 1 mAh) and WO3 electrode. Solid circle and open circle indicates WO3 and FTO, respectively.

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