Field of the invention
The present invention pertains to use of non-noble metal catalyst for electrodes used in the cells of alkaline electrolysis stack. More particularly, the present invention uses manganese as a catalyst in its different forms of Manganese oxide (MnOx).
Description of the Related Art
Today, Hydrogen as an energy carrier, has become increasingly important, mainly in the last two decades. It owes its popularity to the increase in the energy costs caused by the uncertainty in the future availability of oil reserves and also to the concerns about global warming and climate changes, which are blamed on manmade CO2 emissions associated with fossil fuel use, so, even if the cost of hydrogen production is higher than fossil fuels, its own unique set of properties is finding new applications in many directions: Industry, Mobility, Energy storage, Power To Gas, Power To Liquid, Aviation, Submarines, Hydrogen-sea ships.
Hydrogen, now, has been perceived as a valid alternative to fossil fuels in many applications because of its advantage of being a clean fuel, considering that its use emits almost nothing other than water. Additionally, it can be produced using any energy source, with renewable energy being most attractive, making it one of the solutions to sustainable energy supply in the so-called new "hydrogen economy”.
There are several ways to produce hydrogen by electrolysis:
PEM water electrolysis, also named as solid polymer electrolysis (SPE), whose operation principles are basically the reverse of a PEM Fuel Cell. Intensive studies were carried out to reduce the membrane cost. In the early 1970s, small-scale PEM water electrolysers were used for space and military applications. However, the short durability of the membrane makes PEM electrolysers too expensive for general applications. This technology may offer good energy efficiency, higher production rates, and more compact design than traditional alkaline water electrolysis technologies. However, special requirements are needed for several of its components (e.g., expensive polymer electrolyte membrane, porous electrodes, and current collectors), which are its serious disadvantages.
HTE (High-Temperature Electrolysis, also known as steam electrolysis, is performed using a solid oxide electrolysis cell (SOEC). It adopts a solid oxide, as the electrolyte, in the process, this because SOEC operates at elevated temperatures, typically between 500 and 850 ºC.
Alkaline Water Electrolysis, especially powered by renewable energy sources, can be integrated into a distributed energy system to produce hydrogen for end use or as an energy storage medium. Compared to the current major methods used for hydrogen production, briefly described above, alkaline water electrolysis is considered the most reliable technology. However, it still needs much work to improve its present efficiency. Further research is required to increased efficiency.
The production of Hydrogen as an energy carrier is mainly done using a process called electrolysis done in cells of electrolyser stack. For this process, Noble metal oxides are commonly used to catalyse electrodes (as electro catalysts). Ruthenium dioxide (RuO2), iridium dioxide (IrO2), and mixed oxides containing these two noble metals have been proved to have high electro catalytic activity for the O.E.R(Oxygen Evalution Reaction). IrxRuyTazO2 as an anode electro catalyst achieved an overall cell voltage low, with an energy consumption lower and high efficiency.
However, using noble metals and catalysis in both electrodes in general leads to very high cost increase for the electrolyzer, so it is preferred to catalyze only one of the electrodes.
Our search at US & European Patent Database reveals several pending and issued patents relating to the use of non-noble metals to catalyze electrodes of an electrolyser stack.
The Publication no: US Patent US5069988A assigned to Battery Technologies Inc is titled as Metal and metal oxide catalyzed electrodes for electrochemical cells. In this invention Porous electrodes for use in fuel cells and other electrochemical cells are disclosed. Principally, the electrodes a catalytically active layer on a porous conductive substrate, which catalytically active layer is derived from non-noble metals. The loading of the catalytically active layer is lower in terms of weight of catalyst per unit area of geometrical electrode surface than heretofore. Several alternative methods of forming the electrode are taught, including impregnating a porous conductive substrate with a metal salt solution, followed by chemical or thermal formation of the porous catalytically active layer; or mixing the catalytically active material with the material of the porous conductive substrate, followed by fabrication of the electrode; or depositing pyrolitic carbon from the gas phase onto a porous conductive substrate, at elevated temperatures in a gas atmosphere. The electrode may also have a porous metallic current collector, and also a further gas diffusion layer. If used as a fuel cell anode, a further small amount of noble metal is included in the porous catalytically active layer. Porous electrodes of this invention have particular utility in alkaline primary or secondary cells as auxiliary gas recombining electrodes, especially as oxygen consuming auxiliary transfer electrodes.
The US Patent US3649361A by United Technologies Corp is titled as Electrochemical cell with manganese oxide catalyst and method of generating electrical energy. An electrochemical cell is described which includes a gas diffusion cathode, an alkaline electrolyte and operates at room temperature. The electrochemical cell has an improved gas diffusion cathode which comprises a finely divided, electrically conductive carbon powder and a base metal catalyst of a manganese oxide, or a manganese oxide with one or more other base metal catalysts. Such a cell provides performance approaching that of a cell including, a diffusion cathode with a platinum catalyst. A method of generating electrical energy from such a cell is also described.
The Publication no: US20040096728A1 by BDF IP Holdings Ltd is titled as Non-noble metal catalysts for the oxygen reduction reaction. A Non-noble metaltransition metal catalysts can replace platinum in the oxidation reduction reaction (ORR) used in electrochemical fuel cells. A RuxSe catalyst is prepared with comparable catalytic activity to platinum. An environmentally friendly aqueous synthetic pathway to this catalyst is also presented. Using the same aqueous methodology, ORR catalysts can be prepared where Ru is replaced by Mo, Fe, Co, Cr, Ni and/or W. Similarly, Se can be replaced by S.
The Publication no: US20100086823A1 is assigned to Sumitomo Chemical Co Ltd and it titled as Membrane-electrode assembly and fuel battery using the same. The invention discloses a membrane-electrode assembly, containing an electrode catalyst containing a base metal complex, in which exchange current density i0 obtained from a Tafel plot, which is related to current density and voltage, is 5.0×10-4 Acm-2 or more, and in which a Tafel slope obtained from the Tafel plot is 450 mV/decade or less; and a membrane-electrode assembly, containing catalyst layers each containing an electrode catalyst on both sides of an electrolyte membrane, in which at least one of the catalyst layers comprises a non-noble metal-based electrode catalyst, and in which the electrolyte membrane is a hydrocarbon-based electrolyte membrane.
[0013] Our search on non-patent databases revealed efforts done in this direction that are worth noting:
• Noble metal-free bifunctional oxygen evolution and oxygen reduction acidic media electro-catalysts
http://www.nature.com/articles/srep28367
• Manganese Oxides As Anode Catalysts for Electrolysis: In Situ Raman and Corrosion Studies
http://ma.ecsdl.org/content/MA2015-03/3/708
• MnO2-based nanostructures as catalysts for electrochemical oxygen reduction in alkaline
https://patents.google.com/scholar/13702506555356318391?q=manganese&q=catalyst&q=cathode&scholar
• Manganese dioxide as a new cathode catalyst in microbial fuel cells
https://patents.google.com/scholar/8942988011836094809?q=manganese&q=catalyst&q=cathode&scholar
Despite the existence of several related arts, the challenge still remains to fully replace the noble metals as catalyst such as Manganese based MnO2 (for catalyzing electrodes of an alkaline electrolyser stacks), which can be synthesized by firstly extracting Manganese metal from Manganese sulfate solution using Electrochemical Membrane Reactor and then calcinating The Electrode at approximately 480 Deg C followed with cooling to transform the metallic Manganese layer on the Electrode into Manganese dioxide form.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a non-noble metal catalyst for both electrodes is used as an effective solution to overcome existing disadvantages.
According to another aspect of the invention, a non-noble metal catalyst is used in place of high cost of conventional catalysts (such as Pd, Ru) which are being generally used to catalyze only one of the two electrodes.
One more aspect of the invention is to use a non-noble metal catalyst so as to enable both the electrodes to be catalyzed thus enhancing the efficiency of electrolyser;
Yet another aspect of the invention is to provide a non-noble metal catalyst so as to avoid the production of two separate types electrodes (anode and cathode) which are required to be stored & managed as two separate items to distinguish them from each other.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawing. It is to be noted, however, that the appended drawing illustrates only typical embodiments of this invention and is therefore not to be considered limiting of its scope, and for the invention may admit to other equally effective embodiments.
Figure 1 depicts a typical non noble electrochemical deposition process to be used to catalyse electrodes of an alkaline electrolyser stack ;
DETAILED DESCRIPTION
Generally, an electrolysis process in an Alkaline Electrolyser stack is achieved by the use of Two Electrodes (cathode and Anode) in each cell of stack. The role of catalysts is precisely that of lowering the activation energy (i.e. lower the overvoltage ie reach the minimum voltage threshold) at which the water splitting reaction takes place at the hands of the current. The catalysts allows an improvement in the system in terms of performance (therefore the current consumption).
The reactions in the basic alkaline electrolysis are the following:
• At Anode (positive), the Oxygen Evolution Reaction (OER)
4OH-?>O2+ 2H2O + 4e-E0 = +0,402 V
• At Cathode (negative), the Hydrogen Evolution Reaction (HER)
4H2O + 4e-?2H2 + 4OH-E0 = -0,828 V
The overall reaction corresponds to the splitting of water into oxygen and hydrogen molecule.
2H2O ? 2H2 + O2E0 = 1,23 V

Oxide reductions Potential (Eº) ratios are theoretical without considering losses and overvoltage. Moreover, the effective potentials (Eº) also depend on a number of barriers have to be overcome, which depend on the electrolysis cell components: the boundary layers at an electrode surface, electrode phase, electrolyte phase, separator, and electrical resistances, the alkaline electrolyte liquid concentrations, the temperature and operating pressure.

Moreover, the effective potentials (Eº) also depend on electrolyte (25-30% KOH by weight), are observed potential (Eº) which can usually differ between 2.0 V and 2.5 V and beyond.

The role of catalysts is precisely that of lowering the activation energy, ie lower the overvoltage ie reach the minimum voltage threshold at which the water splitting reaction takes place at the hands of the current, allowing an improvement of the system in terms of performance (therefore the current consumption).

However, there are some non-noble, less expensive metals that also present electrocatalytic activity and are being introduced for use in oxygen and hydrogen evolution reactions. Additionally, during designing an electrode, it is normally doped or coated with more stable and active layers. The doping material may be chosen from a wide range of metals. For example, Li (Lithium) doping increases the electrical conductivity of the electrode material, favouring the OER.

Among the non-noble metals, the manganese has proved to be among the most promising catalysts, in different forms of Manganese-oxide (MnOx ).

Figure 1 depicts a typical non-noble metal (Manganese) deposition process on Electrode carried out in an electrochemical membrane reactor. This procedure for the deposition of the manganese on the electrodes involves the following materials:
• Manganese (II) Sulfate Hydrate, =99.99% trace metals basis
• Ammonium Sulfate, =99.0%
• Sulfuric Acid, 99.999%
• Ammonia, anhydrous, =99.98%
• Ammonium Sulfide, 20 wt. % in H2O
• Selenium Dioxide, 99.999% trace metals basis

Procedure as explained in Figure 1.

An electrochemical membrane reactor is used. The compartments separation membrane is necessary in order to avoid the mixing of the bath solutions different in pH values. The separation membrane is represented from an anion-exchange one.

The catholyte (the alkaline electrolyte of the cathodic compartment) is prepared by dissolving analytical grade manganese sulfate (35 g/l) and ammonium sulfate (130g/l) in distilled water, along with Selenium dioxide (40 mg/l) acting as performance improvement agent. Ammonia and sulfuric acid are used to adjust the pH of the catholyte solution in order to reach the value of 7.5. The anolyte (the acidic electrolyte of the anodic compartment) is a 0.5 M sulfuric acid solution.

The manganese sulfate solution is purified by precipitations of metal sulfide. The separation is based on the varying solubility of metals in sulfide solution. Ammonium sulfide (NH4) 2S was used in the precipitations of metal sulfide.

This technique is used to separate Mn2+ from other metals such as Cu2+, Zn2+, Co2+, Ni2+ and Fe2+, since these other metal ions are precipitated as metal sulfides while Mn2+ ions remain in solution. This process can be performed repeatedly until the composition of the catholyte meets the requirements of electrochemical deposition.
The electrode is calcinated in a muffle furnace at 480° C for 10 hours in order to transform the metallic manganese layer of the electrode into the manganese dioxide form. After cooling, the electrode is ready to be inserted in the cell of an alkaline Electrolyser stack.
Manganese is one of the most common metals, of easy extraction, low toxicity and high cheapness. It performs its catalytic activity, as all the transition "d" metals, thanks to the accessibility, from the energy point of view, of the orbitals "d", and then it acts as a reaction intermediate opening alternative mechanisms that require less activation energy. Manganese is known for its catalytic activity in the oxidation of water in biological processes of photosynthesis PSII, in the form of WOC (Water-Oxidazing Complex).
Manganese in the form of Mn-Oxy has special properties that make them attractive as catalysts for many reactions. The best form to be used is represented from nanometric sized particles that have largest surface thus showing a highest active area. The metal oxides are organized into poly nuclear structures in which there is one or more metal ions which would promote onset of multi-electrons type reactions-complex. Having binders not easily oxidizable, they show high stability, and they can be prepared in several ways due to high versatility for electro deposition, supported by alumina, Zeolite or other similar ceramic material, or sintered.
About manganese dioxide (MnO2), it has been shown that it has good catalytic activity, similar to the one of enzymes found in nature, due to its structural rearrangement that leads to a wider spatial structure, presenting an higher number of oxygen atoms in the structures that form bridged bonds with the reactants. This explains the increasing of activity during the first period of usage, as observed experimentally.
Its catalytic activity is achieved through an oxide layered structure. After oxidation, thanks to the layered structure, the water molecules can more easily interact with manganese ions at lower oxidation number that form a sort of defects in the ordinated structure. Furthermore, the size of the synthetic nanometric patterns ensures that most of the active sites for catalysis are on the surface, thus allowing greater accessibility to water molecules. In fact the manganese dioxide molecules, under certain conditions, pass to dimanganese trioxide increasing the amorphous character of the catalyst, and favoring its stratification with an increase of the catalytic sites in a manner similar to that one observed in the photosynthesis process for the manganese oxide and calcium in the WOC. Experimentally, the hydroxides and oxides of manganese show high catalytic activity for water oxidation in electrochemical systems, due to the presence of Mn (III) ions on the surface of Mn (II) or Mn (IV).
In conclusion, the evidences show that the catalytic activity is due to the layered structure and is favored by the amorphous character; the nano-sized increases it, offering a higher catalytic surface. In the production of hydrogen through electrolytic processes, the oxides of manganese for the water oxidation (for the Oxygen Evolution Reaction, shortly OER), result to be good catalysts, especially if in a strong alkaline environment (pH higher than 9) as the one present in the alkaline electrolysis (due to the electrolyte, KOH).
The electro deposition process promotes a layered structure, due to the slow aggregation of the particles of manganese to the support, subsequently oxidized by calcination resulting in a structure probably amorphous, but it is important to highlight the importance in the catalyst activity of the procedure and the operating conditions used to carry out the electro deposition (temperature, current, time, etc.).
Systems based on different transition metal oxides by manganese (example Ir and Ru) show versatility of these metals which makes them suitable to both the evolution of hydrogen and oxygen (HER and OER). Since the mechanism is based on an oxide-reductive process, the catalyst is reasonably active both in the oxidation and in the reduction, allowing the use of such catalysts for both electrodes.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

We Claim:
1. A method to catalyze electrodes in an Electrochemical membrane reactor , such method comprising the steps of,
purification of manganese sulfate solution comprising Mn2+, Cu2+,Fe2+, Zn2+, CO42, (MnSO4)in sulfide solution such as Ammonium sulfide (NH 4) 2S in order to separate Mn2+ extracting Manganese metal from Manganese sulfate solution through electro deposition (electroplating); and calcinating the extracted Manganese metal layer of the Electrode at approximately 480 degrees for 10 hours (in order to transform the metallic manganese layer of the electrode into the manganese dioxide form) followed with cooling.
so as method to enable both the electrodes to be catalyzed to enhance the efficiency of the Alkaline electrolyser stack.
2. The method of claim 1, wherein the purification process is performed repeatedly until composition of the catholyte meets the requirements of electro chemical deposition.
3. The method of claim 1, wherein the electrode is calcinated in a muffle furnace for 10 hrs in order to transform the metallic layer of the electrode into MnO2 form followed by cooling.
4. The method of claim 1, further comprising the use of non-noble metal catalysed Electrodes in an alkaline electrolyser stack to produce Hydrogen to enhance energy efficiency in electrolysis technologies.
5. The method of claim 1, wherein the catalyzed electrodes are further used to produce Hydrogen at a lower activation energy at which water splitting reaction takes place at the hands of current.
6. The method of claim 1, wherein the purification of further comprises the use of electrochemical membrane reactor with compartment separation membrane in order to avoid the missing of the bath solutions having different pH values.
7. The method of claim 1, wherein the manganese sulfate solution is purified by precipitations based on the varying solubility of metals in a sulfide solution.
8. A pair of electrodes in each cell an electrolyser stack, such an electrode comprising of:
Non-noble catalyst depositions, such as Manganese MNO2 and its forms (Achieved by calcinating the extracted Manganese metal layer of at approximately 480 degrees into MnO2 form, followed by cooling
so that the catalyst increases the electrical conductivity of the electrode material, that now requires reduced activation energy.