Teflon hydrogen diffusion

At temperatures below 100°C, Eh values are usually measured directly using electrochemical techniques. At elevated temperatures, however, it is usually more convenient to measure hydrogen pressures in equilibrium with the system being investigated. The Teflon hydrogen diffusion membrane is a device which directly measures H2 pressures in equilibrium with the... 

This report considers Teflon ( trademark of Dupont) hydrogen diffusion membranes and zirconia pH sensors. The development of these sensors represents a significant advance in the environmental monitoring of En and pH conditions at elevated temperatures and pressures. 

The fermentation tests were carried out in shake flasks, STR and FBR. The effect of the following parameters was investigated the amount of gel and the total cell concentration in the bioreactor the addition of hydrogen acceptor (acetone), instead of air, to activate the electron transport in the respiratory chain and the use of Teflon-made filters as air diffusers to reduce air bubble dimension and increase oxygen solubility. 

Hydrogen easily diffuses through the smallest cracks and spaces, and it is important to perform hydrostatic tests on as many of the components and connections as possible and to use pipe dope and tape that is compatible with hydrogen. Teflon tape is color coded for specific applications. Yellow tape is the color... 

Hydrogen gas fuel and air (O2) are fed to anode and cathode Pt catalyst powder layers, respectively. The Pt catalysts is Teflon-bonded to porous carbon sheets to form gas-diffusion electrodes, with a catalyst loading of about 1.0 mg/cm. The Pt anode and cathode are separated by a thin inert porous matrix that is filled with concentrated phosphoric acid. The cell operates at 200°C (to improve the electrode kinetics), with a cell voltage of about 0.67 V at a current density of 0.150 A/cm. Most voltage losses occur at the air cathode. The hydrogen gas must be pure because sulfur and carbon monoxide poison the Pt anode catalyst. This type of fuel cell is commercially available today, with more than 200 systems installed all over the world in hospitals, hotels, office buildings, and utility power plants. 

The packaging approach utilized for tliis battery is similar to that for nickel—hydrogen single cylindrical cells as shown in Figure 23. The silver electrode is typically the sintered type used in rechargeable silver—zinc cells. The hydrogen electrode is a Teflon-bonded platinum black gas diffusion electrode. 

Figure 9 shows the effects of different experimental arrangements on the distribution curves of 2.5 X 10" M KF. In one instance, the perforated platinum electrode was replaced by a snugly fitting Teflon disk, located about 3 cm. from the interface, provided with only two small holes (Vs inch in diameter) to allow fluid transfer. The apparent distribution coeflBcient is about four times that found for unhindered diffusion. Hydrogen ion transfer is appreciably less. Constitutional supercooling see below and Ref. 146) in the interface region may perhaps have contributed to this rise of the distribution coeflBcient. Qualitatively similar results were found for HF. 

These cells operate only with hydrogen as the anode fuel and, moreover, the hydrogen must be pure since sulphur compounds and carbon monoxide adversely affect the performance of the Pt catalyst. Each cell consists of two teflon-bonded gas diffusion electrodes on a porous conducting support (see Fig. 10.21). At both anode and cathode the catalyst is platinum particles dispersed on carbon and a recent success has been a reduction in Pt loading from 10 mg cm to 0.75 mg cm ". The electrolyte is concentrated phosphoric acid absorbed onto a solid matrix and the cell operates at 200°C to improve the electrode kinetics. The cells are then mounted in stacks to increase the power output. 

A polypropylene gas diffusion screen is placed behind the hydrogen electrode to allow hydrogen gas and oxygen gas to diffuse to the back side of the negative electrode with the Teflon backing. 

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