Layered composite membranes based on porous PVDF coated with a thin, dense PBI layer for vanadium redox flow batteries

A commercial porous polyvinylidene fluoride membrane (pore size 0.65 μm, nominally 125 μm thick) is spray coated with 1.2–4 μm thick layers of polybenzimidazole. The area resistance of the porous support is 36.4 mΩ cm2 in 2 M sulfuric acid, in comparison to 540 mΩ cm2 for a 27 μm thick acid doped polybenzimidazole membrane, and 124 mΩ cm2 for PVDF-P20 (4 μm thick blocking layer). Addition of vanadium ions to the supporting electrolyte increases the resistance, but less than for Nafion. The expected reason is a change in the osmotic pressure when the ionic strength of the electrolyte is increased, reducing the water contents in the membrane. The orientation of the composite membranes has a strong impact. Lower permeability values are found when the blocking layer is oriented towards the vanadium-lean side in ex-situ measurements. Cells with the blocking layer on the positive side have significantly lower capacity fade, also much lower than cells using Nafion 212. The coulombic efficiency of cells with PVDF-PBI membranes (98.4%) is higher than that of cells using Nafion 212 (93.6%), whereas the voltage efficiency is just slightly lower, resulting in energy efficiencies of 85.1 and 83.3%, respectively, at 80 mA/cm2

Enzymatic Biofuel Cells Using Fe-N/CNT and Enzyme Molecules as Both Anodic and Cathodic Catalysts

???????????? ???????????????????????? ????????? ?????????????????? ????????? ????????? ??????????????????. ????????? ???????????? ?????? ??????????????? ??????????????? ???????????? ????????? ???????????? ?????? ??????????????????, ????????? ?????? ????????????. ??? ??????????????? ???????????? ????????????????????? ???????????? ???????????? Fe-N ??????????????? Fe-N/CNT??? ?????? ????????? ??? ????????? ??? ????????? ???????????? ???????????????. Fe-N/CNT??? ???????????? ?????? ?????? ????????? ?????? ??? ?????????????????? ?????? ????????? ????????? ?????? ?????? ??? ????????? ??????????????? ????????????. ???????????? ?????? Fe-N/CNT??? ????????? ?????? ??????????????? ???????????? ????????? ???????????????????????? ?????? ????????? ?????? ????????? ??? ?????????, ???????????? ?????? ?????????????????? ??????????????? ???????????? ????????????(Glucose Oxidase, GOx)??? ?????? ????????? ?????????????????? Fe-N/CNT??? Fe-N??? ???????????? ?????? ??????????????? ??????????????? ????????????. ????????? ????????? ???????????? ?????? ???????????? ??????????????? ????????? ???????????????, ?????? ???????????? Kit??? ???????????? ???????????? ?????? ?????? ???????????????

Membraneless enzymatic biofuel cells using iron and cobalt co-doped ordered mesoporous porphyrinic carbon based catalyst

Iron and cobalt co-doped ordered mesoporous porphyrinic carbon (FeCo-OMPC) is employed as the catalyst for both electrodes in membraneless enzymatic biofuel cells (EBCs). FeCo-OMPC is used for catalyzing oxygen redox reaction (ORR), while GOx/[FeCo-OMPC/CNT] is utilized as a catalyst for a series of glucose oxidation reaction (GOR) and hydrogen peroxide oxidation reaction (HPOR). The onset potential of the ORR by FeCo-OMPC is 0.31 V vs. Ag/AgCl, while that of HPOR by FeCo-OMPC/CNT and GOR-HPOR by GOx/[FeCo-OMPC/CNT] are both 0.12 V. The activity of this catalyst is better than previously reported similar catalysts due to the presence of Co species and high metal contents. As a result, the concentration of H2O2 generated by GOR is 1.02-1.56 mM when the same glucose concentration as human blood is used. In addition, the EBC using GOx/[FeCo-OMPC/CNT] and FeCO-OMPC shows the maximum power density of 21.3 +/- 2.97 mu W cm(-2) with open circuit voltage (OCV) of 0.17 +/- 0.016 V. These values are significantly higher than those of EBC using the competitive Fe-NI CNT catalyst (0.11 V and 9.6 mu W cm(-2)). Moreover, the OCV is close to the expected value by CV (0.19 V), confirming that the FeCo-OMPC catalyst can be used for implantable bioelectronics, such as biosensors and electroceuticals

Dual catalytic functions of biomimetic, atomically dispersed iron-nitrogen doped carbon catalysts for efficient enzymatic biofuel cells

We report that the performance of enzymatic biofuel cell (EBC) can be boosted by exploiting the dual function of iron- and nitrogen-codoped carbon nanotube (Fe-N/CNT) catalysts. The Fe-N/CNT is directly used as a cathode catalyst for oxygen reduction reaction while it is combined with glucose oxidase (GOx) and polyethylenimine (PEI) to form GOx/PEI/[Fe-N/CNT] for catalyzing the overall oxidation reactions including glucose oxidation reaction at the anode. The cathode employing Fe-N/CNT catalyst shows excellent onset potential and current density (0.29 V and of 0.9 mA cm(-2)). In anode, GOx/PEI/[Fe-N/CNT] shows proper onset potential and current density (0.17 V and 74.3 mu A cm(-2)) with the injection of 8 mM glucose solution. More quantitatively, its Michaelis-Menten constant and maximum current density are 139.4 mM and 347.1 mu A cm(-2), respectively, and its catalytic activity is well maintained preserving 81.2% of its initial value even after four weeks. The EBC comprising Fe-N/CNT at the cathode and GOx/PEI/[Fe-N/CNT] at the anode exhibits the maximum power density (MPD) of 63 mu W cm(-2). This is the first report that demonstrates the possibility of the heme mimicking nanocatalyst as both anodic and cathodic catalysts for EBCs

Aqueous redox flow battery using iron 2,2‐bis(hydroxymethyl)‐2,2′,2′‐nitrilotriethanol complex and ferrocyanide as newly developed redox couple

An all-iron aqueous redox flow battery using iron (Fe) 2,2-bis(hydroxymethyl)-2,2',2'-nitrilotriethanol (BIS-TRIS) complex (Fe(BIS-TRIS)) and Ferrocyanide (Fe[CN](6)) as redox couple is newly suggested. The redox potential of Fe(BIS-TRIS) is -1.11 V (vs Ag/AgCl) and this makes Fe(BIS-TRIS) appropriate as active material for anolyte, while Fe(CN)(6) is proper for catholyte due to its excellent redox reactivity, redox potential, and cheap cost. According to quantitative evaluations, Fe(BIS-TRIS) does not produce any side reactions and is more stable than Fe triethanolamine (TEA) (Fe(TEA)) complex that is conventionally considered for the purpose. This fact is confirmed by computational analysis using density functional theory. In the calculation, energy barrier of Fe(BIS-TR1S) suppressing the occurrence of undesirable side reactions is higher than that of other Fe-ligand complexes, indicating that desirable redox reaction of Fe(BIS-TRIS) occurs more stably. In redox flow battery (RFB) tests, RFBs using Fe(BIS-TRIS) do not show any side reactions even after 250 cycles with excellent performances, such as capacity of 11.7 Ah L-1. and coulombic efficiency and capacity retention rate of 99.8 and 99.9%, respectively. This corroborates that RFBs using Fe(BIS-TRIS) have excellency in both performance and stability, while the cheap cost of BIS-TRIS and Fe(CN)(6) enhances the economic benefit of RFBs.11Nsciescopu

Vanadium Redox Flow Batteries Using <i>meta</i>-Polybenzimidazole-Based Membranes of Different Thicknesses

15, 25, and 35 μm thick <i>meta</i>-polybenzimidazole (PBI) membranes are doped with H₂SO₄ and tested in a vanadium redox flow battery (VRFB). Their performances are compared with those of Nafion membranes. Immersed in 2 M H₂SO₄, PBI absorbs about 2 mol of H₂SO₄ per mole of repeat unit. This results in low conductivity and low voltage efficiency (VE). In ex-situ tests, <i>meta</i>-PBI shows a negligible crossover of V³⁺ and V⁴⁺ ions, much lower than that of Nafion. This is due to electrostatic repulsive forces between vanadium cations and positively charged protonated PBI backbones, and the molecular sieving effect of PBI’s nanosized pores. It turns out that charge efficiency (CE) of VRFBs using <i>meta</i>-PBI-based membranes is unaffected by or slightly increases with decreasing membrane thickness. Thick <i>meta</i>-PBI membranes require about 100 mV larger potentials to achieve the same charging current as thin <i>meta</i>-PBI membranes. This additional potential may increase side reactions or enable more vanadium ions to overcome the electrostatic energy barrier and to enter the membrane. On this basis, H₂SO₄-doped <i>meta</i>-PBI membranes should be thin to achieve high VE and CE. The energy efficiency of 15 μm thick PBI reaches 92%, exceeding that of Nafion 212 and 117 (N212 and N117) at 40 mA cm^–2

Electrochemical activity studies of glucose oxidase (GOx)-based and pyranose oxidase (POx)-based electrodes in mesoporous carbon: Toward biosensor and biofuel cell applications

A simple study using a fixed amount of mesoporous carbon (MSU-F-C) was performed for the comparison of pyranose oxidase (POx) and glucose oxidase (GOx) in their electrochemical performance under biosensor and biofuel cell operating modes. Even though the ratio of POx to GOx in the glucose oxidation activity per unit weight of MSU-F-C was 0.35, the ratios of POx to GOx in sensitivity and power density were reversed to be 6.2 and 1.4, respectively. POx with broad substrate specificity and an option of large scale production using recombinant E. coli has a great potential for various electrochemical applications, including biofuel cells.

Nanoscale enzyme reactors in mesoporous carbon for improved performance and lifetime of biosensors and biofuel cells

Nanoscale enzyme reactors (NERs) of glucose oxidase in conductive mesoporous carbons were prepared in a two-step process of enzyme adsorption and follow-up enzyme crosslinking. MSU-F-C, a mesoprous carbon, has a bottleneck pore structure with mesocellular pores of 26 nm connected with window mesopores of 17 nm. This structure enables the ship-in-a-bottle mechanism of NERs, which effectively prevents the crosslinked enzymes in mesocellular pores from leaching through the smaller window mesopores. This NER approach not only stabilized the enzyme but also expedited electron transfer between the enzyme and the conductive MSU-F-C by maintaining a short distance between them. In a comparative study with GOx that was simply adsorbed without crosslinking, the NER approach was proven to be effective in improving the sensitivity of glucose biosensors and the power density of biofuel cells. The power density of biofuel cells could be further improved by manipulating several factors, such as by adding a mediator, changing the order of adsorption and crosslinking, and inserting a gold mesh as an electron collector. (C) 2010 Elsevier B.V. All rights reserved.