Experimental and Modeling Studies of Paper Based Methanol Fuel Cell

Paper based devices, such as such as paper based fuel cells, batteries and microbial fuel cells, have attracted substantial attention recently, because of their ability to generate reasonable power suitable for micro-nano systems (MNS), for short term use. It would be an added advantage for these systems if paper based devices could be integrated with them. The reason for choosing paper as the core substrate, can be attributed to the excellent properties of paper, e.g., porosity, capillarity and biodegradability, which make paper a self-sufficient substrate/medium to transport fluids within the system. This not only reduces the complexity of pumping the fluids into the paper based systems but also imparts many other advantages including low cost, ease of fabrication, and ease of disposal. These paper based energy sources have the potential to be used as a power source for single use point-of-care devices, which currently employ batteries. In the present work, we have developed a T-shaped paper based fuel cell with methanol (CH3OH) as the fuel. The cell consists of two L-shaped paper strips of Whatman filter paper, separated by a poly acryl amide (PAM) gel separating them. This gel accounts for the transport of ions from anode to cathode and vice-versa. 4 M NaOH is used as the electrolyte with CH3OH (varying concentration) and the resulting solution is referred as anolyte and potassium permanganate (KMnO4) along with 4 M H2SO4 serves as the catholyte. Three different concentrations of CH3OH in the anolyte, i.e. 2 M, 4 M and 6 M are used. The paper acts as a medium for transporting the anolyte and catholyte to the respective electrodes (carbon cloth). The cell delivered the maximum power density of 0.9 (mW/cm2) at 4 M CH3OH + 4 M NaOH and 1 M KMnO4 + 4 M H2SO4. Electrochemical impedance spectroscopy (EIS) is also done at 2 M, 4 M and 6 M CH3OH. This study reveals that the polarization resistance (Rp) is minimum for 4 M (CH3OH), with variations in the ohmic resistances (Rohm). Nitrogen doped graphene oxide (N-GO), N-rGO, NiCo2O4 and N-rGO-NiCo2O4 are synthesized and implemented as catalysts in our paper cell and the cell performance is measured using each of the above mentioned catalysts. In order to obtain an improved cell performance, NiCo2O4 micro-spheres with a porous surface are synthesized hydrothermally. Their structure and morphology are characterized using scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The catalyst is used in different electrode combinations. With the catalyst only at the anode, the cell delivered a peak power density of 2.33 mW/cm2 and limiting current density of 7.6 mA/cm2. This implicates that the catalyst is capable of enhancing the methanol electro-oxidation which takes place at the anode. At this condition, chronoamperometric measurement (current density versus time) is also performed to study the cell?s ability to deliver a sustained current density. It is found that with 0.25 ml of anolyte and catholyte, the cell is capable to deliver current even after 15 min of operation. Further, a composite catalyst consisting of N-rGO and NiCo2O4 is synthesized hydrothermally and employed as a catalyst in different electrode combinations in the cell, as shown in figure 1. The catalyst when present at both electrodes along with 4 M CH3OH and 1 M KMnO4 in the anolyte and catholyte respectively, deliver the best performance of 3.66 mW/cm2 peak power density and 11.6 mA/cm2 maximum current density, leading to an increase of 300% in the peak power density, as compared to a cell without any catalyst. This implies that the presence of N-rGO enhances the electrocatalytic activity of NiCo2O4. A mathematical model using Butler-Volmer equation has been used to predict the current densities at experimental cell voltages, at different CH3OH concentrations in the anolyte. The numerically obtained dc polarization curves agree well with those obtained from the experimental measurements. More results about the cell performance using different combination of catalysts will be presented in the conference