Preparation and evaluation of advanced electrocatalysts for phosphoric acid fuel cells

Results are presented for hydrogen oxidation and hydrogen oxidation poisoned by carbon monoxide at levels between 0 and 30%. Due to the high activities that are now being observed for our platinum based electrocatalysts, the hydrogen concentrations were reduced to 10% levels in the gas supplies. Perturbation techniques were used to determine that a mechanism for the efficient operation of our porous gas diffusion electrodes is diffusion of the carbon monoxide out of the electrode structure through the electrolyte film on the electro-catalyst. A survey of the literature on platinum group materials (PGM) was carried out so that an identification of successful electrocatalysts could be made. Two PGM electrocatalysts were prepared and performance data for hydrogen oxidation in hot phosphoric acid in the presence of high carbon monoxide concentrations showed that they matched the best platinum on carbon electrocatalysts but with an electrocatalyst cost that was half of the platinum catalyst cost

Preparation and evaluation of advanced catalysts for phosphoric acid fuel cells

The platinum electrocatalysts were characterized for their crystallite sizes and the degree of dispersion on the carbon supports. One application of these electrocatalysts was for anodic oxidation of hydrogen in hot phosphoric acid fuel cells, coupled with the influence of low concentrations of carbon monoxide in the fuel gas stream. In a similar way, these platinum on carbon electrocatalysts were evaluated for oxygen reduction in hot phosphoric acid. Binary noble metal alloys were prepared for anodic oxidation of hydrogen and noble metal-refractory metal mixtures were prepared for oxygen reduction. An exemplar alloy of platinum and palladium (50/50 atom %) was discovered for anodic oxidation of hydrogen in the presence of carbon monoxide, and patent disclosures were submitted. For the cathode, platinum-vanadium alloys were prepared showing improved performance over pure platinum. Preliminary experiments on electrocatalyst utilization in electrode structures showed low utilization of the noble metal when the electrocatalyst loading exceeded one weight percent on the carbon

Preparation and evaluation of advanced electrocatalysts for phosphoric acid fuel cells

Two cooperative phenomena are required the development of highly efficient porous electrocatalysts: (1) is an increase in the electrocatalytic activity of the catalyst particle; and (2) is the availability of that electrocatalyst particle for the electromechanical reaction. The two processes interact with each other so that improvements in the electrochemical activity must be coupled with improvements in the availability of the electrocatalyst for reaction. Cost effective and highly reactive electrocatalysts were developed. The utilization of the electrocatalyst particles in the porous electrode structures was analyzed. It is shown that a large percentage of the electrocatalyst in anode structures is not utilized. This low utilization translates directly into a noble metal cost penalty for the fuel cell

Controlling the corrosion and cathodic activation of magnesium via microalloying additions of Ge

The evolution of corrosion morphology and kinetics for magnesium (Mg) have been demonstrated to be influenced by cathodic activation, which implies that the rate of the cathodic partial reaction is enhanced as a result of anodic dissolution. This phenomenon was recently demonstrated to be moderated by the use of arsenic (As) alloying as a poison for the cathodic reaction, leading to significantly improved corrosion resistance. The pursuit of alternatives to toxic As is important as a means to imparting a technologically safe and effective corrosion control method for Mg (and its alloys). In this work, Mg was microalloyed with germanium (Ge), with the aim of improving corrosion resistance by retarding cathodic activation. Based on a combined analysis herein, we report that Ge is potent in supressing the cathodic hydrogen evolution reaction (reduction of water) upon Mg, improving corrosion resistance. With the addition of Ge, cathodic activation of Mg subject to cyclic polarisation was also hindered, with beneficial implications for future Mg electrodes

CORRELATIONS BETWEEN ELECTROCHEMICAL ACTIVITY AND HETEROGENEOUS CATALYSIS FOR HYDROGEN DISSOCIATION ON PLATINUM

Hydrogen-deuterium exchange rates on platinum surfaces have been compared to equivalent hydrogen molecule and adsorbed hydrogen atom electrochemical oxidation rates on the same surfaces. Over a temperature range of 293 to 3600 K the first order rate con-stants for Hz-Dz exchange and hydrogen molecule electrochemical oxidation are the same, showing that the adsorption-dissociation reaction (T AFEL,BoNHOEFFER-F ARKAS) is rate controlling. The rate of oxidation of the adsorbed hydrogen atom reaction involving electron transfer (VOLMER) is an order of magnitude larger. The hydrogen evolution reaction has been the subject of numerous mechanistic investigations which has resulted in the determination of rea-sonably accepted mechanisms for a number of substrates. All the acceptable reaction paths have one reaction step in common which, in acid electrolyte, is the electronation of hydrogen ions to form neutral hydrogen species adsorbed on the electrode surface. M+H++e- <===t MH This charge transfer step was originally discussed by ERDEy-GRUZ and VOLMER!), and subsequently has been referred to as the Volmer reaction. Two different reaction paths for hydrogen evolution may be distinguished. These two paths differ in the manner in which the adsorbed hydrogen atoms are desorbed from the surface to form molecular hydrogen. T AFEL2) suggested a desorption step which did not involve charge transfer

Preparation and evaluation of advanced electro-catalysts for phosphoric acid fuel cells. Eighth quarterly report, October-December 1981. [Platinum]

In the development of new and highly efficient porous electrocatalysts, two cooperative phenomena are required. The first is an increase in the electrocatalytic activity of the catalyst particle, and the second is the availability of that electrocatalyst particle for the electrochemical reaction. These two processes interact with each other in such a way that improvements in the electrochemical activity must be coupled with improvements in the availability of the electrocatalyst for reaction. Since cost effective and highly reactive electrocatalysts have been developed under this program, the utilization of the electrocatalyst particles in the porous electrode structures is addressed. Based on the performance of the electrocatalysts in porous electrode structures, it is shown that a large percentage of the electrocatalyst in anode structures is not utilized. This low utilization translates directly and dramatically into a noble metal cost penalty for the fuel cell. Dramatic improvements in the cost effectiveness of the fuel cell will be achieved by improvements in electrocatalyst catalyzation technology and electrode structure technology