|Title of Invention||
A PROCESS FOR MANUFACTURE OF CERIA-SUPPORTED PLATINUM AS HYDROGEN-OXYGEN RECOMBINANT CATALYST IN SEALED BATTERIES
|Abstract||A novel ceria-supported platinum catalyst with varying concentration (0.5-4.0 at. %) of platinum that can recombine hydrogen and oxygen quite efficiently is the object of the invention. The catalyst has been synthesized by the solution combustion method for he fIrSt time. The synthesis, characterization and H2-02 recombination efficiencies of this catalyst form the subject matter of the invention.|
Field of Invention
This Invention relates to battery manufacture / technology. This Invention further relates to the field of investigation relating to catalysis. More particularly this Invention relates to development of a hydrogen - oxygen recombination catalyst.
Background of Invention
In the art, the oxygen cycle' in secondary cells has been well known for many years. In 1938, it was known that the oxygen evolving from the positive electrode of a nickel-cadmium cell could be easily reduced at the negative electrode. However, the evolved hydrogen from the negative electrode was oxidized at the positive electrode only extremely slowly. By the 1940s, it was recognized that the way to avoid hydrogen evolution in a nickel-cadmium cell was to have excess negative active material, so that the positive electrode was fully charged and began to evolve oxygen when the negative electrode was still only partially charged. If the evolved oxygen was then reduced at the negative electrode at the same rate as it was evolved at the positive electrode, the negative electrode would remain only partially charged, hydrogen evolution would be suppressed and the cell could then be sealed. It was then found that the rate at which oxygen could be recombined can be increased if a limited amount of electrolyte was used in the cell. The first practical sealed cell using the principle of oxygen recombination was thus produced.
It is to be understood that the application of 'oxygen cycle' to a lead-acid accumulator is much more difficult. The lead-acid cell voltage is about 2V but the decomposition potential of water is only 1.23V. Therefore, the lead-acid cell should
not work in principle, but in practice however the high H2 and O2 over-potentials on positive and negative electrodes respectively enable the electrodes to be charged before H2 and O2 evolve at a substantial rate. The 'oxygen cycle' can be made to operate with lead-acid cells provided that the principles of excess negative material and limited electrolyte are followed. On over charge of the sealed recombining cell, the oxygen from the positive electrode is recombined at the negative electrode thus maintaining the negative in partially charged condition and suppressing the evolution of hydrogen.
In the conventional flooded cell, after both electrodes have been fully charged, the voltage rises to the gassing voltage. In the sealed recombining cell, the voltage profile is at first similar, but once the positive electrode is fully charged the evolved oxygen diffuses to the negative electrode where it reacts with the spongy lead on the surface, thus discharging it. This reduces its potential and causes a dip in the voltage curve. Since the positive electrode in a lead-acid cell accepts charge less efficiently than the negative electrode, during the recharge of a lead-acid battery H2 and O2 are evolved non-stoichiometrically with O2 evolution occurring prior to H2 evolution. The reactions occurring during the oxygen evolution are often stated to be: (a) evolution of oxygen from the positive electrode, (b) reaction of oxygen with spongy lead to form lead monoxide, (c) reaction of lead monoxide with sulfuric acid to form lead sulfate and water, and (d) charging of negative electrode by conversion of lead sulfate to lead.
Some of the principles for successful application of the 'oxygen cycle' include both flat-plate and spirally-wounded small cells. The critical design parameters are: (a) the negative/positive material ratio must ensure that the negative is still only partially charged when the positive is fully charged, (b) the separator electrolyte system must ensure that there is no free electrolyte and the separator must be completely saturated, leaving paths for oxygen to diffuse to the negative electrode, and (c) the grid alloys must have no additives that reduce the hydrogen over-potential of lead; pure lead is used in some designs but it is more usual to employ lead-calcium alloys often with the addition of tin, and (d) the separator is usually an absorbent glass matrix. However, the gelled electrolytes (sulfuric acid/silica gel) are capable of allowing oxygen diffusion after a short period of service because they partially dry out and form micro paths to the negative electrode. Since the acid is limited in volume, it is normal to use slightly higher densities than in conventional cells. The evolution of hydrogen from the negative electrode cannot be entirely suppressed and the sealed cells must therefore have a non-return valve that allows the escape of gases if the pressure becomes too high. This also provides for safety of the ceil in the event of abuse.
Prior art limitations
There is very little in the way of published data on recombinant system design, analysis, performance and applications, not only because of the newness of the technology but also due to the need for secrecy tied with patents and business strategies. As time goes on, these factors will hopefully become less important but on a day-to-day basis these, at present, are real limitations.
Proposed solutions with novei technoiogy
It is hereby informed that this Invention uses a novel ceria-supported platinum catalyst with varying concentration (0.5 - 4.0 at.%) of platinum that can recombine hydrogen and oxygen quite efficiently, thus circumventing the above stated problems of sealed accumulators. The catalyst has been synthesized by the solution combustion method for the first time. The synthesis, characterization and H2-O2 recombination efficiencies of this catalyst are described in the following description.
The primary object of this Invention is to invent a novel catalyst for manufacturing batteries. It is another object of the Invention to invent a novel catalyst which is platinum based.
Further it is another object of the Invention to invent a novel catalyst which will simplify the process of manufacturing sealed batteries.
Further objects of the Invention will be clear from the following description.
A process for manufacture of ceria-supported platinum as hydrogen-oxygen recombinant catalyst in various sealed batteries comprises the following steps.
The combustion mixture for the preparation of 1 at. % Pt/Ce02 contained (NH4)2 Ce(N03)6 (cerie ammonium nitrate). H2PtCl6 (chloroplatinic acid) and C2H6N4O2 (oxalyldihydrazide) in the mole ratio 0.99: 0.01: 2.33; oxalyldihydrazide
(ODH) prepared from diethyl oxalate and hydrazine hydrate, acts as a fuel. 10 g of (NH4)2 Ce (N03)6. 0.095 g of H2PtCl6 and 5.175 g of ODH were dissolved in the minimum volume of water in a borosilicate dish of 130 cm3 capacity. The dish containing this redox mixture was introduced into a muffle furnace maintained at 350°C. Initially, the solution boiled with frothing and foaming and underwent dehydration. At the point of complete dehydration, the surface ignited, burning with a flame (-1000°C) and yielded a voluminous solid product within 5 minutes.
A hydrogen-oxygen recombinant catalyst of ceria-supported platinum wherein the platinum has varying composition ranging from 0.5 at.% to 4 at.%.
Now the Invention will be described in detail in the following specification and with reference to the drawings.
Figure 1(A) of the drawings indicate in the form of a table. H2 - O2 recombination efficiencies % of 0.5 at. % Pt/ CeO 2 Catalyst.
Figure 1(B) of the drawings indicate in the form of a table, H2 - O2 recombination efficiencies % of 1 at.% Pt/Ce02 catalyst.
Figure 1(C) of the drawings indicate in the form of table, H2-O2 recombination efficiencies % of 2 at.% Pt/ Ce02 catalyst.
Figure 1(D) of the drawings indicate in the form of table, H2-O2 recombination efficiencies % of 4 at.% Pt/CeOa catalyst.
Figure 2 of the drawings indicate graphically the X-ray intensity vs Bragg angle.
(a) Synthesis of the catalyst and its physical characterization
The combustion mixture for the preparation of 1 at.% Pt/Ce02 contained (NH4)2Ce(N03)6 (cerie ammonium nitrate). H2PtCl6 (choloroplatinic acid) and C2H6N4O2 (oxalyldihydrazide) in the mole ratio 0.99 : 0.01 : 2.33; oxalyldihydrazide (ODH) prepared from diethyl oxalate and hydrazine hydrate acts as a fuel. 10 g of (NH4)2Ce(N03)6 (E. Merck India Ltd.. 99.9%). 0.095 g of H2PtCl6 (Ranbaxy Laboratories Ltd., 99%) and 5.175g of ODH were dissolved in the minimum volume of water in a borosilicate dish of 130 cm3 capacity. The dish containing this redox mixture was introduced into a muffle furnace maintained at 350 °C. Initially, the solution boiled with frothing and foaming and underwent dehydration. At the point of complete dehydration, the surface ignited, burning with a flame (--1000 °C) and yielding a voluminous solid product within 5 min. Similarly, 0.5 at.%, 2 at.% and 4 at.% Pt/Ce02 were prepared.
The X-ray diffraction (XRD) patterns of the Pt/Ce02 catalyst with varying concentration of Pt were recorded on a Siemens, D-5005 X-ray Diffractometer using CuKα radiation with a scan rate of 2° min-1 The X-ray diffraction pattern of prepared catalyst agrees well with CeO2 in fluorite structure. There is no change in the XRD patterns of the catalyst before and after their prolonged contact with concentrated
sulfuric acid and potassium hydroxide solutions (Figure 2). X-ray photoelectron spectra (XPS) of these catalysts were recorded on an ESCA-3 Mark II spectrometer (V G Scientific Ltd.. England) using AlKα radiation (1486.6 eV) and it is found that in these catalysts platinum is present in Pt2+ and Pt4+ oxidation states.
(b) Hydrogen-oxygen recombination efficiencies of the Pt/Ce02 catalyst
Hydrogen-oxygen recombination experiments have been performed with an electrolyzer containing Ni-plaques as electrodes in 6 M KOH. The evolved H2 and O2 gases from the electrolyzer have been allowed to pass through a quartz-tube reactor containing different amounts of the catalyst. The length and diameter of the reactor tube were 20 cm and 6 mm, respectively. The catalyst-bed temperature was measured by a fine chromel-alumel thermocouple immersed in the catalyst mass and was found to be in the range 50-100 °C depending on the flow rate and the amount of the catalyst. The amount of gas escaping from the catalyst-bed after recombination has been measured and accordingly H2-O2 recombination efficiencies have been calculated for different catalysts for their varying amounts at various flow rates of H2-O2 gases (Table 1). From the flow rate and the recombination efficiency for H2 and O2 to give H2O, absolute rate of this reaction is calculated from the equation:
where F = flow rate of hydrogen, x = fractional conversion, W= weight of the catalyst and v= stoichiometric coefficient (equal to 2 for this reaction). Substituting the values
from Table 1, rate of the reaction calculated is found to be in the range 10-75 iimol g
Advantages of the Invention
It is claimed that the synthetic procedure of the catalyst preparation described herein is novel and this catalyst could be effectively employed as a H2-O2 recombinant catalyst in various sealed storage batteries, viz. valve regulated lead-acid cells/batteries, alkaline nickel-Iron, nickel-cadmium and nickel-metal hydride cells/batteries. It is also claimed that:
(a) This catalyst can be effectively employed for recombining H2 and O2 evolving from the nuclear reactors;
(b) This catalyst could be used along with Nafion-membrane for its humidification in polymer electrolyte membrane fuel cells;
(c) This catalyst is highly active for low temperature NO reduction by NH3, CO. CH4 and C3H8 and also selective catalytic reduction of NO;
(d) This catalyst is active towards CO, CH4, C3H8 and NH3 oxidation;
(e) This catalyst could as well be used as a three-way catalyst wherein NO, CO and hydrocarbon can be reduced to N2, CO2 and H2O (in presence of excess O2).
It is to be noted that the object of the description is to explain the salient features of the Invention. It is further to be noted that this description in no way limits the scope of the Invention. It is further understood that within the scope of the invention various modifications and amendments are possible. The scope of the monopoly is claimed in the following description.
(1) A process for manufacture for ceria-supported platinum as hydrogen-oxygen recombinant catalyst in various sealed batteries comprising the following steps.
The combustion mixture for the preparation of 1 at.% Pt/Ce02 contained (NH4)2 Ce(N03)6 (cerie ammonium nitrate), H2PtCl6 (chloroplatinic acid) and C2H6N4O2 (oxalyldihydrazide) in the mole ratio 0.99: 0.01: 2.33; oxalyldihydrazide (ODH) prepared from diethyl oxalate and hydrazine hydrate, acts as a fuel. 10 g of (NH4)2Ce(N03)6,0.095 g of H2PtCl6 and 5.175 g of ODH were dissolved in the minimum volume of water in a borosilicate dish of 130 cm3 capacity. The dish containing this redox mixture was introduced into a muffle furnace maintained at 350°C. Initially, the solution boiled with frothing and foaming and underwent dehydration. At the point of complete dehydration, the surface ignited, burning with a flame (--1000°C) and yielded a voluminous solid product within 5 minutes.
(2) A process for manufacture of ceria-supported platinum H2-O2 recombinant
catalyst for various sealed batteries as claimed in claim 1 wherein the said
process is executed for obtaining 0.5 at.%, 2 at.% and 4 at.% Pt /CeO2.
(3) A ceria-supported platinum H2-O2 recombinant catalyst wherein the platinum
has varying composition ranging from 0.5 at.% to 4 at.%.
(4) A catalyst for use in various sealed storage batteries.
(5) A process for manufacture of ceria-supported platinum H2 - O2 recombinant
catalyst in various sealed batteries as described in the specification.
(6) A ceria-supported platinum H2- O2 recombinant catalyst as described in the
|Indian Patent Application Number||308/MAS/2000|
|PG Journal Number||20/2006|
|Date of Filing||24-Apr-2000|
|Name of Patentee||M/S. INDIAN INSTITUTE OF SCIENCE|
|Applicant Address||BANGALORE 560 012|
|PCT International Classification Number||H01M 10/34|
|PCT International Application Number||N/A|
|PCT International Filing date|