Showing papers by "Niels J. Bjerrum published in 2012"
TL;DR: In this article, the PBI membranes were shown to be irreversibly cured by the thermal treatment and the improved physicochemical characteristics of the membranes after curing were further illustrated by a dramatically improved long-term durability of the corresponding fuel cell MEAs.
Abstract: Phosphoric acid doped polybenzimidazole (PBI) has emerged as one of the most promising electrolyte materials for proton exchange membrane (PEM) fuel cells operating under anhydrous conditions at temperatures of up to 200 °C. The limited long-term durability of the membrane electrode assemblies (MEAs) is currently hampering the commercial viability of the technology. In the present study, thermoset PBI membranes were prepared by curing the membranes under inert atmosphere at temperatures of up to 350 °C prior to the acid doping. The systematic membrane characterizations with respect to solubility, phosphoric acid doping, radical-oxidative resistance and mechanical strength indicated that the PBI membranes were irreversibly cured by the thermal treatment. After curing, the PBI membranes demonstrated features that are fundamental characteristics of a thermoset resin including complete insolubility, high resistance to swelling and improved mechanical toughness. Additionally, the thermal treatment was found to increase the degree of crystallinity of the membranes. The improved physicochemical characteristics of the membranes after curing were further illustrated by a dramatically improved long-term durability of the corresponding fuel cell MEAs. During continuous operation for 1800 h at 160 °C and 600 mA cm−2, the average cell voltage decay rate of the MEA based on the cured membrane was 43 μV h−1. This should be compared with an average cell voltage decay rate of 308 μV h−1 which was recorded for the MEA based on its non-cured counterpart.
143 citations
TL;DR: In this article, an acid-base polymer membrane is prepared by doping of imidazolium polysulfone with phosphoric acid for high temperature proton exchange membrane fuel cells.
107 citations
TL;DR: In this paper, a modified version of the Adams fusion method was used to deposit IrO 2 on the support surface and a series of electrocatalysts were prepared with a composition of (IrO 2 ) x (TaC) 1− x, where x represents the mass fraction of irO 2 and was equal to 0.1, 0.3, 0., 0.5, 0, 7, 0.9 and 1.5.
81 citations
TL;DR: Tungsten carbide (WC) promoted palladium and palladium-cobalt (Pd-Co) nanocatalysts are prepared and characterized for formic acid electrooxidation as discussed by the authors.
74 citations
TL;DR: In this paper, the Co-20%SO2PBI membrane exhibited a tensile strength of 16 MPa at room temperature and an H2-air fuel cell peak power density of 346 mW cm−2 at 180 °C at ambient pressure.
Abstract: Poly(aryl sulfone benzimidazole) (SO2PBI) and its copolymers with poly[2,2′-p-(phenylene)-5,5′-bibenzimidazole] (pPBI), termed as Co-SO2PBI, were synthesized with varied feeding ratios of 4,4′-sulfonyldibenzoic acid (SDBA) to terephthalic acid (TPA). Incorporation of the stiff para-phenylene and flexible aryl sulfone linkages in the macromolecular structures resulted in high molecular weight copolymers with good solubility. The chemical stability towards radical oxidation was improved for SO2PBI and its copolymer membranes due to the electron-withdrawing sulfone functional groups. Upon acid doping, the membrane swelling was reduced and the mechanical strength was improved, as compared with their meta structured analogues. At an acid doping level of 11 mol H3PO4 per average molar repeat unit, the Co-20%SO2PBI membrane exhibited a tensile strength of 16 MPa at room temperature and an H2-air fuel cell peak power density of 346 mW cm−2 at 180 °C at ambient pressure. Durability tests with the membrane under a constant current density of 300 mA cm−2 at 160 °C showed a degradation rate of 6.4 μV h−1 during a period of 2400 h, which was significantly lower than that for meta PBI membranes with a similar acid doping level.
69 citations
TL;DR: In this article, antimony doped tin oxide nanoparticles were synthesized and further doped with an inorganic proton conducting phase based on tin pyrophosphates as the catalyst support.
57 citations
TL;DR: Tungsten carbide (WC) nanopowder was tested as a non-platinum cathode electrocatalyst for polymer electrolyte membrane (PEM) water electrolysers, operating at elevated temperatures.
56 citations
TL;DR: In this article, a composite membrane system using a perfluorosulfonic acid membrane (Aquivion™) as matrix and phosphoric acid as proton conducting electrolyte was developed.
56 citations
TL;DR: In this paper, a new proton conductor based on niobium phosphates was synthesized using Niobium pentoxide and phosphoric acid as precursors, and the existence of hydroxyl groups in the phosphates were confirmed and found to be preserved after heat treatment at 500 °C or higher.
Abstract: A new proton conductor based on niobium phosphates was synthesized using niobium pentoxide and phosphoric acid as precursors. The existence of hydroxyl groups in the phosphates was confirmed and found to be preserved after heat treatment at 500 °C or higher, contributing to an anhydrous proton conductivity of 1.6 × 10−2 S cm−1 at 250 °C. The conductivity increased with water content in the atmosphere and reached 5.8 × 10−2 S cm−1 under pure water vapour at the same temperature. The conductivity showed good stability in the low water partial pressure range of up to 0.05 atm. The metal phosphates are of high interest as potential proton conducting electrolytes for fuel cells operational in an intermediate temperature range.
42 citations
20 citations
17 Oct 2012
TL;DR: In this paper, the potential advantages of PEM cells over more abundant alkaline electrolyzers is that they were shown to be reversible [21, 31, 69] and they can produce hydrogen from water in the electrolysis mode, while electricity can be inversely produced in the fuel cell mode.
Abstract: One of the potential advantages of PEM cells over more abundant alkaline electrolyzers is that they were shown to be reversible [21, 31, 69]. The type of an electrochemical cell working both as a fuel cell and a water electrolyzer is called a unitized regenerative fuel cells (URFC) [13, 38, 67, 70]. These devices produce hydrogen fromwater in the electrolysis mode, while electricity can be inversely produced in the fuel cell mode. This mode of working is beneficial when the lack of electricity changes with the excess energy available (periods of low consumption) [61].
04 Jun 2012
TL;DR: In this paper, different corrosion resistant stainless steels, nickel-based alloys, pure nickel, Ta-coated stainless steel (AISI 316L), niobium, platinum and gold rods were evaluated as possible materials for use in the intermediate temperature (200-400 °C) acidic water electrolysers.
Abstract: Different corrosion resistant stainless steels, nickel-based alloys, pure nickel, Ta-coated stainless steel (AISI 316L), niobium, platinum and gold rods were evaluated as possible materials for use in the intermediate temperature (200-400 °C) acidic water electrolysers. The corrosion resistance was measured under simulated conditions (molten KH2PO4) corresponding to the proton-conducting solid acids or transition metal phosphates as electrolytes. It was shown that, unlike at temperatures below 200 °C, gold is unstable with respect to corrosion in molten KH2PO4. Platinum demonstrated high corrosion resistance and the anodic and cathodic limits were for the first time found for the electrolyte. Nickel, niobium, Inconel®625, Hastelloy®C-276 and Ta-coated stainless steel (AISI 316L) demonstrated high corrosion stability and can be recommended as construction materials for bipolar plates.
04 May 2012
TL;DR: In this paper, commercial TaC and Si3N4 powders were tested as possible electrocatalyst support materials for the OER for PEM water electrolysers, operating at elevated temperatures.
Abstract: Commercial TaC and Si3N4 powders were tested as possible electrocatalyst support materials for the Oxygen Evolution Reaction (OER) for PEM water electrolysers, operating at elevated temperatures. TaC and Si3N4 were characterised by thermogravimmetric and differential thermal analysis for their thermal stability. The Adams fusion method was implemented to deposit IrO2 on the support surfaces. A series of electrocatalysts was prepared with a composition of (IrO2)x(TaC/ Si3N4)1-x,where x represents the mass fraction of IrO2 and was equal to 0.1 (only for TaC), 0.3, 0.5, 0.7, 0.9 and 1. The thin-film method was used for electrochemical analysis of the prepared electrocatalysts. SEMEDX, BET and powder conductivity measurements were used as complementary techniques to complete characterisation of the electrocatalysts. Additionally, they were compared in their properties with previously reported data for a SiC-Si support. The stability of the electrocatalysts was assessed by estimation of reversibility of the anodic/cathodic processes.
27 Apr 2012
01 Jan 2012
TL;DR: CARISMA International Conference on Medium and High Temperature PEM Fuel Cells Copenhagen, 3-5 September 2012 as mentioned in this paper, presented by Lars Nilausen Cleemann Technical University of Denmark (DK).
Abstract: Book Editor Lars Nilausen Cleemann Technical University of Denmark (DK) 3 CARISMA International Conference on Medium and High Temperature PEM Fuel Cells Copenhagen, 3 – 5 September 2012
01 Jan 2012
TL;DR: CARISMA International Conference on Medium and High Temperature PEM Fuel Cells Copenhagen, 3-5 September 2012 as mentioned in this paper, presented by Lars Nilausen Cleemann Technical University of Denmark (DK).
Abstract: Book Editor Lars Nilausen Cleemann Technical University of Denmark (DK) 3 CARISMA International Conference on Medium and High Temperature PEM Fuel Cells Copenhagen, 3 – 5 September 2012