Hiroya Abe1
Tohoku University1
For the realization of sustainable development goals, regional ecosystems must develop and use universal sustainable technologies, and the widespread use of renewable energy is essential for this purpose. Thus, there is an urgent need to develop renewable energy production and storage devices. A wood-derived carbon is a promising electrode as an energy device because its high porosity improves the carbon's surface area Recently, we have reported a highly active wood-derived electrochemical catalyst for oxygen reduction reaction which occurs on the cathode of metal-air batteries and fuel cells (1). The pyrolyzed wood performed high porosity and high catalytic activity. Pyrolysis is required to control the atmosphere at high temperatures and under inert gas, resulting in being expensive and cumbersome. Herein, we report the direct laser-pyrolysis of wood chips for an anode and cathode with a commercial blue laser and establish a three-in-one zinc-air battery.<br/>Paulownia was used as a wood carbon source. Wood chips were pyrolyzed with the blue laser under the ambient atmosphere. The irradiated area became black and metallic. The obtained carbon had macro-scale pores confirmed by an optical microscope and showed the graphitic peaks confirmed by Raman spectra. The electric resistance was improved by increasing the intensity of the blue laser, and the obtained carbon performed highly active electrocatalytic activity by adding metal sources as catalysts.<br/>We confirmed the electrocatalytic activity of the cathode for the oxygen reduction reaction. In this study, the Fe(NO3)3 was used as a metal source and added to the wood before the pyrolysis (wood-Fe). In addition, iron phthalocyanine was modified on the obtained carbon material using the organic solvent as a molecular catalyst (wood-FePc). The molecular catalysts are promising materials since they show superior oxygen reduction activity without any pyrolysis processes (2). The oxygen reduction properties were evaluated in 0.1 M KOH, and the catalytic activity was found to increase in the order of wood, wood-Fe, and wood-FePc. From these results, the wood-derived laser-induced graphene for the electrocatalysts of the oxygen reduction reaction was successfully obtained from wood using the blue laser under the ambient atmosphere.<br/>Finally, we established the three-in-one zinc-air battery. The wood chips have porous structures, resulting in the solvent and electrolyte can be absorbed into their structure. We irradiated the laser at double sides on the wood chip to form the cathode and anode without a connection between each electrode. The FePc and zinc powder loaded onto the cathode and anode, respectively. The open-circuit potential was observed by adding the electrolyte (0.1 M KOH) into the wood chip. The woody battery showed over 10 mA/cm2 and 5 mW/cm2. The wood chip irradiated with the laser at double sides acted as the three-in-one zinc-air battery consisting of the cathode, anode, and separator without an assembly process.<br/>References: 1) Y. Goto, Y. Nakayasu, H Abe, Yuto Katsuyama, T. Itoh and M. Watanabe, Phil. Trans. R. Soc. A (2021) 379: 20200348. 2) H. Abe et al., NPG Asia Materials 11, Article number: 57 (2019)