A novel paper‐based biofuel cell with a series/parallel array structure has been fabricated, in which the cell voltage and output power can easily be adjusted as required by printing. The output of the fabricated 4‐series/4‐parallel biofuel cell reached 0.97±0.02 mW at 1.4 V, which is the highest output power reported to date for a paper‐based biofuel cell. This work contributes to the development of flexible, wearable energy storage device.

A biofuel cell that can generate electricity using only water is expected to be used as a new energy harvester for an emergency power supply. A new 4-series/4-parallel structured paper-substrate biofuel cell was prepared using a fuel supply paper preloaded with glucose and phosphate buffer salts. When a power generation test was conducted by supplying water to the fuel-preloaded paper, the paper-based biofuel cell produced an output approximately 90% (0.84 mW) of that obtained by supplying a phosphate buffer containing glucose as the electrolyte. The open-circuit voltage was 2.1 V, and an LED could be powered by simply supplying water to the cell without using a booster circuit.

We name the Printable Electrochemistry for the development field of printable electrochemical devices [1,2]. Recently, we focus on several paper-based fully-printable electrochemical devices such as biofuel cell [3], biosensor [4] and reference electrode [5].  Paper-based biofuel cell have been attracted as a potential application as energy harvesting power sources in Internet of things (IoT) field [6,7]. In the present study, we newly developed paper-based wearable biofuel cell array fabricated by screen-printing.  Figure 1 shows a schematic illustration of one of our wearable biofuel cell array. The paper-based biofuel cell array exhibited a maximum power density of 1 mW. The present flexible paper-based biofuel cell is highly applicable to the development of low cost, flexible, ubiquitous energy devices. In the present study, we discuss the characteristics of the wearable biofuel cells in detail. [1] I. Shitanda et al., Electrochim. Acta 54 (2009) 4933. [2] I. Shitanda et al., Sens. Actu. B: Chem. 160 (2011) 1606. [3] I. Shitanda et al., Chem. Commun. 49 (2013) 11110. [4] I. Shitanda et al., Chem. Lett. 42 (2013) 1369. [5] I.Shitanda et al., Analyst, 140 (2015) 6481. [6] Claudia W. Narváez Villarrubia et al., Electrochem. Commun, 45 (2014) 44. [7] Carolin Lau et al., Int. J. Hydrogen. Energy, 42 (2015) 14661. Figure 1

There has been considerable recent interest in wearable biofuel cells based on printing technologies.1 Screen-printing technique has following merits; drawing precise pattern of um order, a wide variety of inks, high reproducibility, and low cost. Thus, screen-printing has been widely used for fabrication of electrochemical devices such as dye-sensitized solar cells, biosensors and corrosion sensor. 2-5 Recently, we prepared a screen-printed paper-based biofuel cell using porous carbon inks and showed its high output power. 6 In the present study, we newly demonstrated a screen-printed paper-based biofuel cell which consisted of lactose oxidase-modified and billirubin oxidase-modified porous carbon electrode fabricated on the paper substrate. Firstly, the characteristics of the bioanode and biocathode were investigated independently by the three-electrode method; the bioanode or biocathode was connected to a potentiostat. A Ag|AgCl reference electrode and Pt wire counter electrode were placed in the electrolyte solution. Then, electrochemical response of the BFC was examined. References 1. W. Jia, G. Valdes-Ramirez, A. J. Bandodkar, J. R. Windmiller, J. Wang Angew. Chem. Int. Ed., 52, 7233 (2013). 2. M. Itagaki, Y. Nakano, I. Shitanda, K. Watanabe, Electrochim. Acta , 56, 7975 (2011). 3. I. Shitanda, S. Takamatsu, K. Watanabe, M. Itagaki, Electrochim. Acta, 54, 4933 (2009). 4. I. Shitanda, A. Okumura, M. Itagaki, K. Watanabe, Sens. Actu. B-Chem, 139, 292 (2009). 5. I. Shitanda, T. Yamaguchi, Y. Hoshi, M. Itagaki, Chem. Lett. 42, 1369 (2013). 6. I. Shitanda, S. Kato, Y. Hoshi, M. Itagaki, S. Tsujimura, Chem. Comm. 49, 11110 (2013).