Development of Fe/N/C Type Oxygen Reduction Catalysts Using Carbon Supports Derived from Cellulose Paper by a Microwave Method
Authors: Akiyama Zen , Mizuno Taisei , Suginaga Soichiro , Shiroishi Hidenobu , Saito Morihiro , Kyotani Mutsumasa , Okada Tatsuhiro 
Published: December 2024

Introduction

Effective utilization of abundant forest resources is crucial in Japan, which has vast forest reserves. Cellulose, which constitutes half of plants, has recently garnered attention as a novel material, such as cellulose nanofiber. Kyotani et al. reported that high-yield carbon materials retaining the original shape can be obtained by high-temperature treatment of cellulose-based paper treated with methanesulfonic acid1.We have been preparing Fe/N/C oxygen reduction catalysts using the carbon materials prepared by the method as a support; however, the oxygen reduction activity was insufficient. This study aimed to enhance the oxygen reduction reaction (ORR) activity by employing the microwave method for the preparation of carbon supports, synthesis of catalyst precursors, and drying treatment.

Experimental

Cellulose paper (toilet paper (TP), Nippon Paper Crecia) was immersed in 1.0 M methanesulfonic acid and air-dried for more than two days in a container with a filter attached to the top. The air-dried sample was sandwiched between two carbon plates, placed in an electric furnace, and heat-treated at 800°C for 1 h under Ar atmosphere with a heating rate of 5.5°C/min to obtain a carbonized sample. The sample was heat-treated using microwave oven (ER-SS17A, TOSHIBA) (denoted as MWtre). The sample was pulverized into carbon powder, mixed with 1,10-phenanthroline monohydrate, zinc acetate dihydrate, iron(II) acetate, and Milli-Q water, and heated and stirred for 30 min. Subsequently, the catalyst precursor slurry was obtained by heating using a microwave oven (RE-S5C-W, SHARP) (denoted as MWref). The obtained catalyst precursor slurry was dried using a microwave oven (ER-SS17A, TOSHIBA) to obtain the catalyst precursor (denoted as MWdry). The heat treatment was carried out in two stages. In the first stage, the catalyst precursor was placed in a SUS316 sealed container, replaced with Ar, heated to 800°C at 14°C/min, and then quenched to room temperature to prepare an intermediate material. In the second stage, the intermediate material was placed on a quartz boat and heat-treated at 1050°C for 20 min under Ar flow to obtain the catalyst.
The oxygen reduction activity of the prepared catalyst was evaluated using the rotating ring-disk electrode (RRDE) method. A 2.00 mg/mL catalyst-2-propanol suspension, prepared by sonication and shaking, was cast on the GC electrode of a Pt ring-glassy carbon (GC) disk electrode (φ 6 mm), air-dried, and then 0.1 wt% Nafion® was cast and air-dried to prepare a catalyst-modified electrode. The evaluation of ORR activity was performed in 0.1 M sulfuric acid using the modified electrode as the working electrode, a GC electrode as the counter electrode, and RHE as the reference electrode.

Results and discussion

Fig. 1 shows the polarization curve and the efficiency of four-electron reduction (%H2O) obtained by the RRDE method. For comparison, the results for the catalyst prepared using the conventional method (refluxing for 24 hours followed by drying using a rotary evaporator) are also shown in Fig. 1 (quoted as EVAdry). The onset potential (@0.1 mA mg−1) derived from the oxygen reduction reaction was improved by 0.012 V compared to the conventional method. The efficiency of 4-electron reduction (@0.6 V vs. RHE) was improved by 8.9 – 21.1% compared to the conventional method.

References

(1) M. Kyotani, K. Hiratani, T. Okada, S. Matsushita, and K. Akagi, Global Challenges, 1, 1700061 (2017).

Figure 1