Stefan V. Slavov

A proton-conducting solid state H2S—O2 fuel cell. 1. anode catalysts, and operation at atmospheric pressure and 20–90°C

Abstract A stable solid state H2S—O2 fuel cell has been developed and operated at 1 atm and 20–90°C. A series of anode catalysts has been examined using Nafion® as a common proton conducting membrane; those containing Pd and Pt were found to be effective using H2 or H2S as the anode feed gas, but MoS2—C catalysts were effective for use of H2S but not for H2. The highest potential attained using H2S and Pd/C catalyst was 722 mV (theory: 1140 mV). When H2S was used as anode feed the potential decreased up to 35% over 24 h as sulfur was deposited on the anode. The efficiency of the cell increased with temperature up to 90°C.

A proton-conducting solid state H2S–O2 fuel cell: 2. Production of liquid sulfur at 120–145°C

A proton-conducting solid state H2S–O2 electrochemical cell has been operated at 120–145°C and 235–510 kPa continuously for extended periods, in both fuel cell and electrolysis modes. In fuel cell mode, the products are liquid sulfur, steam and electrical power. Operation at elevated pressures enables the Nafion membrane to remain moist. Anode catalysts Pd/C, Pt/C, Pd–Pt/C and MoS2, admixed with 35% Teflonized carbon, are each stable and durable. Sulfur does not block or poison anode catalyst sites. The membrane is impervious to H2S.

A proton-conducting solid state H2S–O2 fuel cell. 3. Operation using H2S–hydrocarbon mixtures as anode feed

Abstract A H2S–O2 electrochemical cell has been operated for periods up to 10 days using mixtures of H2S with hydrocarbons as anode feed, without loss of activity. The anode catalysts include supported metals, such as Pd/C and Pt/C, and metal sulfides, including MoS2, CoS2 and WS2 admixed with teflonized carbon. When the feed is a mixture of H2S with methane and ethane, the hydrocarbons are not oxidized. The performance of a MoS2–C anode catalyst is unaffected by either hydrocarbons or CO2 in the feed. In contrast, Pd/C anode catalyst gradually loses activity when the feed is a mixture of H2S with both hydrocarbons and CO2. Sustainable power generation of 250 μW / cm 2 has been attained using 3% H2S/97% CH4. Sulfur is recovered as liquid product at 120–145°C and 235–510 kPa.

Mechanism of silation of alumina and silica with hexamethyldisilazane

Abstract The silation of γ—Al2O3 and SiO2 with hexamethyldisilazane (HMDS) has been examined over the temperature range 150-450°C. The products and sequence of the surface reactions have been determined, and a mechanism is proposed. Silation of A12O3. At all temperatures and feed rates of HMDS the initial gaseous product is methane. As the reaction progresses, hexamethyldisiloxane (HMDSO), ammonia, and nitrogen are formed. The quantity of each of these products decreases with increasing temperature. Initially, HMDS reacts with surface sites to generate pendant OSiMe3 and NHSiMe3 moieties. At temperatures over 300°C the predominant subsequent reaction is elimination of methane by reaction of the pendant silyl groups with acidic surface hydroxyls. At lower temperatures reactions between silyl groups to form HMDSO, protonation of amino groups to form ammonia, and redox reactions to form elemental nitrogen predominate over methane elimination. Silation of SiO2. In contrast to Al2O3 the reaction of SiO2 produces ammonia and HMDSO with lesser amounts of methane and nitrogen. No methane is produced during reactions below 300°C. Ammonia is the initial product detected, followed by HMDSO. The amount of methane and nitrogen produced increases, and the amount of ammonia and HMDSO produced decreases, with increasing temperature of reaction. The initial reaction forms NH3 and pendant oSiMe3 groups. The major subsequent reaction is the reaction of neighboring pairs of oSiMe3 groups to form HMDSO, at all temperatures 150-450°C. A second, minor, competing subsequent reaction is the reaction of neighboring hydroxyl and oSiMe3 groups to eliminate CH4 and form bridging oSiMe2 0 groups, at temperatures 300°C or higher.