Final Report - Novel Approach to Non-Precious Metal Catalysts

Abstract

This project was directed at reducing the dependence of PEM fuel cell catalysts on precious metals. The primary motivation was to reduce the cost of the fuel cell stack as well as the overall system cost without loss of performance or durability. Platinum is currently the catalyst of choice for both the anode and the cathode. However, the oxygen reduction reaction (ORR) which takes place on the cathode is an inherently slower reaction compared to the hydrogen oxidation reaction (HOR) which takes place on the anode. Therefore, more platinum is needed on the cathode than on the anode to achieve suitable fuel cell performance. As a result, developing a replacement for platinum on the cathode side will have a larger impact on overall stack cost.The drawbacks of using platinum as an ORR catalyst include its price, scarcity, and susceptibility to forming oxides at voltages of interest for efficient fuel cell operation. The price of platinum has more than doubled during the time period between the drafting of the proposal for this project and its completion. The monthly average price in the beginning of 2003 was $620/troy oz and the present price is $1450/troy oz. At these numbers and the 2010 DOE targets of 0.2 g Pt/kW and $30/kW, the cost of fuel cell stack would be over 30% due to platinum. Thus, the specific objectives of the project, as stated in the solicitation, were to produce non-precious metal (NPM) cathode catalysts which reduce dependence on precious metals (especially Pt), perform as well as conventional precious metal catalysts currently in use in MEAs, cost 50% less compared to a target of 0.2 g Pt/peak kW, and demonstrate durability of greater than 2000 hours with less than 10% power degradation. During the term of the project, DOE refined its targets for NPM catalyst activity to encompass volumetric current density. The DOE Multi-Year RD&D Plan (2005) volumetric current density targets for 2010 and 2015 are greater than 130 A/cm 3 and 300 A/cm 3 at 800 mV (IR-free) respectively.The initial approach to achieve these targets was to use vacuum deposition techniques to deposit transition metal, carbon and nitrogen moieties onto 3M's nanostructured thin film (NSTF) catalyst support. While this approach yielded compounds with similar physicochemical characteristics as catalysts reported by others as active for ORR, the activity of these vacuum deposited catalysts was not satisfactory. In order to enhance catalytic activity additional process steps were introduced, the most successful of which was a thermal treatment. To withstand high temperatures (~900 ºC), alternative supports to NSTF were introduced. A variety of carbon fabrics were tested for this purpose. Vacuum deposited materials were used as precursors and physicochemically transformed via thermal treatment to produce substantially better catalytic activity. This activity was further amplified by increasing the surface area of the carbon fabrics which lead to significant gains in fuel cell performance.iii The second synthetic approach was based on 3M...

Preparation and characterization of Ce- and La-doped Ba2In2O5 as candidates for intermediate temperature (100–500°C) solid proton conductors

“…Our short study on stability of the prepared materials in humid atmospheres showed that in most cases the materials were not stable if exposed to the flow of humidified air at RH = 90% and temperatures between 25 • C and 70 • C. The materials mostly decomposed into BaCO 3 and In(OH) 3 . Under a lower humidification of RH = 50% only BIO decomposed, while the other compositions showed higher stability at all temperatures.…”

“…In recent years, more intense research has taken place to develop intermediate temperature fuel cells (100-500 • C) since they combine the advantages of both high and low temperature fuel cells [1][2][3][4][5][6][7][8]. One of the major approaches to achieve this goal involves searching for new electrolyte materials with a sufficiently high ionic conductivity in that temperature range.…”

“…Proton-conducting ceramics attract significant attention due to their potential for proton conduction below 500 • C. Proton conduction in ceramic materials has been reported before [9][10][11][12]. Some doped perovskite-type oxides ABO 3 (e.g., BaCeO 3 , SrCrO 3 , SrZrO 3 ) and related brownmillerite-type oxides (e.g., Ba 2 In 2 O 5 ) have been reported to show mixed oxygen ion, electron and proton conduction, with predominant oxygen ion conduction at high temperatures (above 500 • C) and predominant protonic conduction at low temperatures (below 500 • C). The mechanism of ions (oxygen or proton) incorporation in perovskite and brownmillerite ceramics in presence of oxygen, water vapour or hydrogen has been suggested elsewhere [11][12][13][14].…”

“…The mechanism of ions (oxygen or proton) incorporation in perovskite and brownmillerite ceramics in presence of oxygen, water vapour or hydrogen has been suggested elsewhere [11][12][13][14]. In general, the ion incorporation and the conductivity of these materials is due to the presence of oxygen vacancies, which are usually formed by doping the ideal perovskite A 2+ B 4+ O 3 2− with lower-valent metal M 3+ ions. In order to keep the charge balance, oxygen leaves the structure, forming vacancies.…”

Effect of pretreatment on Pt–Co/C cathode catalysts for the oxygen reduction reaction

“…Non-precious metal catalysts have been proposed for the replacement of platinum in low temperature fuel cells, however the low mass activity and low stability have prevented them from being successfully implemented [1][2][3]. The use of highly dispersed platinum crystallites on high surface area carbon can increase the active surface area and electrocatalytic activity of the catalysts, thereby reducing the Pt loadings in the cell.…”