• Energy Research

It is necessary to apply a nonenzymatic glucose fuel cell using a proton exchange membrane for an implantable biomedical device that operates at low power. The permeability of glucose with high viscosity and a large molecular weight in the porous medium of the diffusion layer was investigated for use in fuel cells. Carbon paper was prepared as an anode diffusion layer, and it was analyzed with a diffusion layer treated with polytetrafluoroethylene (PTFE) and a microporous layer (MPL). When untreated carbon paper was applied, the peak power density (PPD) and open-circuit voltage (OCV) increased as the glucose concentration and flow rate increased. On this occasion, the highest PPD of 17.81 μW cm-2 was achieved at 3 mM and a 2.0 mL min-1 glucose aqueous solution (at atmospheric pressure and 36.5 °C). The diffusion layer, which became more hydrophobic through PTFE treatment, adversely affected glucose permeability. In addition, the addition of an MPL decreased OCV and PPD with increasing glucose concentrations and flow rates. Compared with untreated carbon paper, the PPD was six times lower approximately. Consequently, it was confirmed that the properties of carbon paper, such as low hydrophobicity, high porosity, and thin thickness, would be advantageous for nonenzymatic glucose fuel cells.

It is necessary to apply a nonenzymatic glucose fuel cell using a proton exchange membrane for an implantable biomedical device that operates at low power. The permeability of glucose with high viscosity and a large molecular weight in the porous medium of the diffusion layer was investigated for use in fuel cells. Carbon paper was prepared as an anode diffusion layer, and it was analyzed with a diffusion layer treated with polytetrafluoroethylene (PTFE) and a microporous layer (MPL). When untreated carbon paper was applied, the peak power density (PPD) and open-circuit voltage (OCV) increased as the glucose concentration and flow rate increased. On this occasion, the highest PPD of 17.81 μW cm-2 was achieved at 3 mM and a 2.0 mL min-1 glucose aqueous solution (at atmospheric pressure and 36.5 °C). The diffusion layer, which became more hydrophobic through PTFE treatment, adversely affected glucose permeability. In addition, the addition of an MPL decreased OCV and PPD with increasing glucose concentrations and flow rates. Compared with untreated carbon paper, the PPD was six times lower approximately. Consequently, it was confirmed that the properties of carbon paper, such as low hydrophobicity, high porosity, and thin thickness, would be advantageous for nonenzymatic glucose fuel cells.

Abstract The bendable fuel cell based on polydimethylsiloxane and Ag nanowire current collectors was fabricated and characterized as it is subject to mixed bending and twisting load. The power density of the fuel cell decreased with the increasing twisting angle regardless of the application of bending. However, the fuel cell with the bending component showed higher power densities than that without bending in all twisting angles. By calculating the stress distribution inside the fuel cell using finite-element method, it was found that the higher performance in the bendable fuel cell under both bending and twisting load is due to the stronger compressive stress on a membrane-electrode assembly induced by the bending load. From electrochemical impedance investigation, it was visualized that although the twisting load increases both electrolyte and electrode resistances, this effect seems to be canceled by the bending, leading to the increased performance.

Abstract The bendable fuel cell based on polydimethylsiloxane and Ag nanowire current collectors was fabricated and characterized as it is subject to mixed bending and twisting load. The power density of the fuel cell decreased with the increasing twisting angle regardless of the application of bending. However, the fuel cell with the bending component showed higher power densities than that without bending in all twisting angles. By calculating the stress distribution inside the fuel cell using finite-element method, it was found that the higher performance in the bendable fuel cell under both bending and twisting load is due to the stronger compressive stress on a membrane-electrode assembly induced by the bending load. From electrochemical impedance investigation, it was visualized that although the twisting load increases both electrolyte and electrode resistances, this effect seems to be canceled by the bending, leading to the increased performance.

Abstract We investigate the use of stiffness-controlled polydimethylsiloxane (PDMS) endplates with Young's modulus of 7.50 × 105 Pa and 8.68 × 105 Pa for improving the performance of flexible fuel cells. The maximum power densities of stacks with PDMS endplates with Young's modulus of 7.50 × 105 Pa and 8.68 × 105 Pa are 82 mWcm−2 and 117 mWcm−2, respectively. The flexible fuel cells produce a maximum absolute power of 1.053 W (i.e., the power density is 117 mWcm2) under a bending radius of 15 cm. Interestingly, their impedance spectra reveal that the ohmic and faradaic resistances decrease under the bent condition. Furthermore, the decreased resistance and corresponding performance enhancement are due to the increased compressive force normal to the membrane electrode assembly, which is investigated using a finite element method of stress distribution within the flexible fuel cells. As our experiments show, the faradaic impedance decreases significantly because the bending radius decreases from 36 cm to 15 cm.

Abstract We investigate the use of stiffness-controlled polydimethylsiloxane (PDMS) endplates with Young's modulus of 7.50 × 105 Pa and 8.68 × 105 Pa for improving the performance of flexible fuel cells. The maximum power densities of stacks with PDMS endplates with Young's modulus of 7.50 × 105 Pa and 8.68 × 105 Pa are 82 mWcm−2 and 117 mWcm−2, respectively. The flexible fuel cells produce a maximum absolute power of 1.053 W (i.e., the power density is 117 mWcm2) under a bending radius of 15 cm. Interestingly, their impedance spectra reveal that the ohmic and faradaic resistances decrease under the bent condition. Furthermore, the decreased resistance and corresponding performance enhancement are due to the increased compressive force normal to the membrane electrode assembly, which is investigated using a finite element method of stress distribution within the flexible fuel cells. As our experiments show, the faradaic impedance decreases significantly because the bending radius decreases from 36 cm to 15 cm.

Platinum (Pt) and ruthenium (Ru) were sputtered on an electrolyte membrane and it was used as a membrane-electrode assembly for passive direct methanol fuel cells (DMFCs) operating with high concentration methanol solution (4 M). Thick (Pt of 300 nm and Ru of 150 nm) and thin (Pt of 150 nm and Ru of 75 nm) sputtered catalysts were prepared and their performance was first evaluated to find out the best sputtering conditions showing higher performance. Subsequently, four electrolyte membranes with different surface roughness were prepared to investigate its influence on the performance. As a result, the performance of the passive DMFC showed increasing tendency as the roughness is low, while the performance was decreased as the roughness was high, indicating there exists an optimal roughness of the electrolyte membrane. It was further investigated through morphological study through electron microscopy that such performance variation is attributed to the surface of sputtered Pt–Ru catalyst on the rough electrolyte membrane that adequate roughness induces the increase of reactive area while a too rough surface bears the poor contact of it with gas-diffusion layer.

Platinum (Pt) and ruthenium (Ru) were sputtered on an electrolyte membrane and it was used as a membrane-electrode assembly for passive direct methanol fuel cells (DMFCs) operating with high concentration methanol solution (4 M). Thick (Pt of 300 nm and Ru of 150 nm) and thin (Pt of 150 nm and Ru of 75 nm) sputtered catalysts were prepared and their performance was first evaluated to find out the best sputtering conditions showing higher performance. Subsequently, four electrolyte membranes with different surface roughness were prepared to investigate its influence on the performance. As a result, the performance of the passive DMFC showed increasing tendency as the roughness is low, while the performance was decreased as the roughness was high, indicating there exists an optimal roughness of the electrolyte membrane. It was further investigated through morphological study through electron microscopy that such performance variation is attributed to the surface of sputtered Pt–Ru catalyst on the rough electrolyte membrane that adequate roughness induces the increase of reactive area while a too rough surface bears the poor contact of it with gas-diffusion layer.