The debut of inorganic compounds into the Sulfonated Poly Ether Ether Ketone, with Tungsto phosphorous acid matrix represents a possible solution to increase the efficiency of polymer electrolyte membrane H2O electrolyser. The electrochemical belongingss and morphology of these membranes were studied by Solartron trial system and SEM. Furthermore comparative public presentation of the membranes and accelerator coating methods were reported. The influence of morphology on chemical-physical belongingss of membranes was besides investigated. The composite inorganic SPEEK impregnated with Zirconium oxide and TPA performed at a high current denseness of 1.35 A/cm2 by impregnation decrease method, which closer to 1.4 A/cm2 is observed by conventional coppice surfacing method.
Composite proton exchange membrane
Membrane electrode assembly
Impregnation decrease method
Brush surfacing method
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The development of solid polymer electrolyte ( SPE ) based H2O electrolyzer is looking to be an efficient method of bring forthing high pureness H in big measures with small or no environmental impact [ 1, 2 ] . Water Electrolysis is a really simple procedure that takes H2O and passes a supply of electricity through it utilizing immersed electrodes to divide into positive H ( H+ ) and negative O ( O- ) ions. These H and O ions migrate through the H2O towards the cathode and anodes severally, where negatron transportations allow for the diatomic H2 and O2 molecules to organize at high pureness. The usage of H as a power coevals beginning is minimum at this phase due to its high cost of production.
Because of the challenges that conventional Nafion membranes faces important research late has been devoted to the development of more nonfluorinated polymers [ 3-7 ] Sulphoned Poly ( Ether Ether Ketone ) ( SPEEK ) [ 8-11 ] , Poly ( Benzimidazole ) ( PBI ) , Sulponated Poly sulfone ( PSF ) , Poly ( Ether Sulfone ) ( PES ) , poly ( arylene quintessences ) , polyimides, and polyphosphazene. [ 12-16 ] etc. , have first-class chemical mechanical and thermo oxidative stableness and are low cost. Among these membranes based on aromatic poly ether ether ketone ( PEEK ) were shown to be really assuring for H2O electrolysis application since they possess good mechanical belongingss on grade of Sulfonation ( DS ) .
In add-on, the sulfonic acid group improves the chemical belongingss of the polymer such as H2O consumption and selectivity. Furthermore, the increased solubility in H2O and solvent restrictions improves the application for proton carry oning polymer. SPEEK was selected in this survey. It was reported that the SPEEK membranes could hold a life clip longer than 3000 h [ 17-20 ] which can be used as a proton carry oning membrane stuff. It was besides found the grade of sulfonation has a strong influence on both conduction and stableness of SPEEK.
Recent old ages have witnessed the development of zero spread electrolysis cells [ 21, 22 ] As such, the usage of membranes in zero spread electrolysis cells in the hereafter will increases in direct proportion to the promotion on their synthesis and developmental applications. Heteropolyacids ( HPA ) [ 23-25 ] , have double function of being both hydrophilic and proton conducting. However, HPAs are by and large water-soluble ; the grades of solubility are reduced in composite HPAs, while keeping their high proton conduction. Composite matrix reduces the leaching of HPA.
The aim of this research is to develop a new type of composite membrane by integrating Heteropolyacids such as tungstophopsphoric acid ( TPA ) and Inorganic fillers such as Ti dioxide ( TiO2 ) , silicon dioxide ( SiO2 ) , Zr dioxide ( ZrO2 ) [ 26-28 ] into partly sulfonated polyether quintessence ketone ( PEEK ) polymer matrices.
In this work we have stretched the assorted catalytic preparations to measure if such a method could be applicable to zero spread H2O electrolyzers incorporating a broad scope of current densenesss. Two types of accelerator coating were made on the membranes: Platinum- Platinum by non-equilibrium Impregnation-Reduction ( I-R ) method and Platinum – Iridium oxide by conventional coppice surfacing method. Among all cherished metals, Pt is the most active accelerator for the H development reaction ( HER ) at the cathode and can be applied at moderate burden. Iridium and Ir oxide is good known for its alone electro catalytic belongingss in regard to oxygen development procedures. Since IrO2 [ 29 ] accelerator exhibits high corrosion immune belongingss but somewhat lower electro catalytic activity than RuO2 [ 30 ] . The conventional method coatings were made automatically.
Poly ( ether – ether ketone ) ( PEEK ) was obtained from Victrex® US, Inc. ( 450 PF ) , 1-methyl-2-pyrrolidinone ( NMP ) was obtained from Merck, Titanium dioxide ( TiO2 ) , Silicon dioxide ( SiO2 ) and Zirconium dioxide ( ZrO2 ) and Phosphotungstic acid ( PWA ) were obtained from Sigma Aldrich and were used as received without farther purification.
Synthesis of SPEEK membrane
PEEK was foremost dried at 100 oC in a vacuity oven for 8 h. Then 10 g of the polymer was dissolved in 500 milliliter of concentrated sulphuric acid ( Merck ) and smartly stirred at room temperature for coveted lengths of reaction clip. Then, the polymer solution was bit by bit precipitated over ice-cold H2O under uninterrupted mechanical agitation, and left to settle nightlong. The grade of sulfonation of the polymers used is indistinguishable throughout the experiment. The precipitate was filtered and washed with distilled H2O. It was so dried under vacuity for 8-10 H at 100 oC. The concluding merchandise is the sulfonic acerb signifier of PEEK ( SPEEK ) .
Preparation of SPEEK composite membranes
SPEEK membranes were prepared by fade outing the SPEEK sample in NMP dissolver under changeless stirring to organize a homogeneous solution at 70 oC to which 10 wt % phosphotungstic acid were added indistinguishable among the three and 10 wt % TiO2/SiO2/ZrO2 were added severally and so refluxed at 80 oC for 6 H, to obtain a clear syrupy gel. But higher phosphotungstic acid lading degree has some retreats i.e, loss of the mechanical strength every bit good as leaching out of unbound acid. In order to work out these jobs, the membranes were hot pressed between two Teflon movies at 80 oC for 3 min is required. These attacks have surely improved the mechanical belongingss. The movie was cast on a clean glass home base with the coveted thickness and dried at 80 oC for 12 h. The thickness of the wet composite polymer membrane was between 0.20 and 0.30 millimeter. Then, the composite membranes were detached from the glass tray by adding de-ionized H2O. Finally, the membranes were purified by heating at 70 oC in 3 % H2O2, 15 % H2SO4 and in de-ionized H2O for 1 H, severally.
Ionic conduction and conveyance belongings measurings
Conduction measurings were made for composite membrane by two-probe electric resistance technique, under potentiostatic conditions at a sweep rate of 5 mV.S-1 from 1-Hz to 1-MHz excitement signal. During the measurement each membrane was sandwiched between chromium steel steel home bases and an ion barricading electrodes, the cross-sectional country of the surface was 0.502 cm2. The conduction ( ? ) of the samples in the cross way was calculated from the electric resistance informations, utilizing the relationship ? = L/RA, where A is the Area of the electrodes, L and R are the thickness and bulk opposition of the movies, severally, The R was derived from the high frequence x-axis intercept of the complex electric resistance secret plan.
Water consumption ( Wwd ) after two hours of submergence was determined as the difference in weight ( W ) between the dried and the conceited membranes.
Where Wdry is the mass of the dry membrane.
Ion Exchange Capacity ( IEC )
The ion exchange capacity of the membranes was determined utilizing the titration process [ 31 ] . The dry composite membrane was immersed in 100 milliliter of 0.1M hydro chloride aqueous solution for 48 hour to alter them into H+ signifier. The samples were so washed with distilled H2O to take extra HCl, and so titrated with a standardised Na hydrated oxide solution utilizing phenolphthalein as an index.
The ion exchange capacity ( IEC ) was calculated utilizing the undermentioned equation.
where IEC is the ion exchange capacity ( mequiv. g-1 ) , V the added titrant volume at the tantamount point ( milliliter ) , M the molar concentration of the titrant and is the dry mass of the sample ( g ) .
Water electrolysis to bring forth gaseous H and O ( Eq.1-3 ) is a long-established procedure.
Anode: > ( 1 )
Cathode: > ( 2 )
Cell: > ( 3 )
In this survey, we compare the public presentation capablenesss of SPEEK based membranes with Nafion -117 by I-R method and coppice coating methods at 80 oC. The ensuing Current densenesss versus Voltage are besides compared in Fig. 5 and 6. The experiments were repeated thrice to look into for duplicability.
2.7. Membrane Electrode Assemble ( MEA )
In Impregnation Reduction ( I-R ) method, solutions of Pt anions, such as chloroplatinate,0.01 M ( PtCl6 2- ) , and a reduction agent, typically sodium borohydrate ion 0.2M ( BH4- ) , are revealed to opposite sides of a stationary solid Polymer Electrolyte membrane. ( BH4- ) ions continuously penetrate the membrane and come into contact with ( PtCl6 2- ) ions on the opposite membrane face, at which point the Pt ions are reduced to platinum metal at the membrane surface in conformity with the impregnation decrease method [ 32 ] . The other side of the membrane was impregnated and reduced by IrO2 under the conditions described in old literature [ 33 ] .
In Conventional Brush method, The Catalyst ink was prepared by first making a stock solution of 5 % Nafion solution, isopropyl intoxicant, and on occasion H2O. The stock was sonicated for 30 proceedingss to thoroughly blend the constituents, and so added to the Platinum black and sonicated another 30 proceedingss until a homogeneous suspension was obtained. Similarly the Ir ink is besides made of the same process utilizing iridium oxide salt. The accelerator coatings were made automatically by coppice. The burden of anode accelerator was about 2 milligrams cm-2 IrO2, while the cathode burden was 2 mg cm-2 of Pt.
After the decrease stairss were completed, the MEA was soaked in 0.5M H2SO4 for 2 h. Finally the membranes were immersed in de-ionized H2O for 2 H before re-drying at 80 oC for 12 h. The membrane had an ion exchange capacity of 2.10 mequiv. g-1, a thickness of 0.210 millimeter, and an ionic conduction of all the prepared composite membranes are in the order of 10-2 S.cm-1.
Consequences and treatment
3.1. Fourier Transform Infrared Spectroscopy Analysis
The FT-IR Spectra obtained for the membrane are shown as Fig. 1-3 shows a comparing between typical FTIR spectra of wet membranes of SPEEK/TPA/ ( Ti, Si, Zr O2 ) and of dried membranes of SPEEK/TPA/ ( Ti, Si, Zr O2 ) . The membrane was foremost immersed in deionized H2O for 1 h. Then these moistures membranes were used in FTIR spectra by rapidly after taking the surface attached H2O to find the wetted membrane spectra. The dry membrane spectra were determined after drying the membrane at 100oC for 1 h. There is besides a clear difference between these spectra around the broadband in SPEEK samples looking at 3480cm-1 was due to O-H quiver from sulfonic acid groups interacting with H2O molecules. The presence of soaking up extremums in the scope 1160 to 1100 cm-1 is observed. This indicates the presence of aromatic sulfonate group. The places of quiver manners of all types of M-O bonds were strongly influenced by interaction of Phosphotungstic acid with the polymer and fillers. The remainder of the extremums are assigned as follows: 550 cm-1: Ti-O asymmetric stretching. 1100 cm-1: Si-O stretching quiver. 530-560 cm-1: Zr-O quiver. 1230, 1075 cm-1: O-S-O symmetric stretching quivers. 870 cm-1: Phosphotungstic acid. The sets around 610 cm-1 is due to the symmetric stretching of Ti-O dried membrane. The sets around 1460 cm-1 is due to the asymmetric stretching of Si-O dried membrane. In SPEEK/TPA/Zro2 spectra, the typical Zr-O stretching quivers bands around 1680 cm-1 associated with the formation of a Zr web were present. However, the presence of S=O flexing quivers around 1410 cm-1, confirms the incorporation of sulfonated groups. The strong vibrational sets at 1690-1750cm-1 were observed for the carbonyl group nowadays in polymer anchor, which strength was decreased with the dried membranes due to H-bonding. ( 33 )
IEC – Water uptake
The H2O consumption and ion exchange capacity ( IEC ) plays a critical function in membrane conduction. At higher IEC values, the H2O consumption increased aggressively at a relative rate larger than that observed for lower IEC values, due to the hydration parts near the ions overlapping and the reduced volume fraction of the unfunctionalized stage. Fig. 4 shows the H2O consumption ( % ) and IEC for the membranes. It is observed that the SPEEK composite membranes exhibit lower H2O consumption when compared to pure SPEEK although the additives are hydrophilic and effects in the different IECs. Excessively high degrees of H2O consumption can ensue in membrane dimensional alteration taking to failures in mechanical belongingss. Hence the relationship between IEC and H2O uptake ( % ) plays a important function in membrane morphology.
3.3. Scaning Electron Microscope
Surface morphology of the composite membrane as obtained by SEM are shown in Fig. 5. The distribution of inorganic fillers was comparatively unvarying in the organic matrix. Fig. 5 ( a ) and ( B ) shows the IrO2 coating and Platinum surfacing on the SPEEK membrane by conventional coppice surfacing method. This shows the Agglomerated atoms are observed in the interface every bit good as on the surface of the membranes. Fig. 5 ( degree Celsius ) shows the Pt bed signifiers extensively on the membrane surface, as in non-equilibrium I-R method shows unvarying distribution of the bunchs of Pt atoms. Fig. 5 ( vitamin D ) shows a extremely porous composite membrane of ( Pt/SPEEK-TPA-ZrO2/ IrO2 ) with pore diameters in the scope 2-6 µm. The pore formation in the composite membranes could besides be responsible for the addition in the conductivity activation energy compared to pure SPEEK membranes. The add-on of fillers resulted in a alteration of the composite membranes ; the surface homogeneousness was reduced and an drawn-out porousness was clearly revealed with no grounds of agglomeration.
3.4. Polymer electrolyte membrane electrolysis cell
The public presentation of the composite membranes were evaluated in a individual cell constellation up to current densenesss cell up to current densenesss of 1.45 A/cm2 with a accelerator burden of 2 milligrams /cm2 in the cathode and anode. Fig. 6 and 7 shows the cell electromotive force vs. current denseness curves of MEA prepared utilizing the I-R method and conventional coppice method severally. The H2O electrolysis cell was operated at 80 oC and under atmospheric force per unit area. Fig. 6 shows the consequence of the electromotive force versus current denseness features of the MEAs: ( Pt/Nafion 117/ IrO2, Pt/SPEEK-TPA-TiO2/ IrO2, Pt/SPEEK-TPA-SiO2/ IrO2, Pt/SPEEK-TPA- ZrO2 / IrO2 ) prepared by impregnation decrease method.
Fig. 7 shows the consequence of the electromotive force versus current denseness features of the 2nd MEAs: ( Pt/Nafion 117/ IrO2, Pt/SPEEK-TPA-TiO2 / IrO2, Pt/SPEEK-TPA-SiO2 / IrO2, Pt/SPEEK-TPA-ZrO2 / IrO2 ) prepared by conventional coppice surfacing method.
Note that the current consumed by the electrochemical cell additions with clip and this addition is due to the addition in the cell temperature. It is besides found that there is a higher addition in the cell current at increased recess temperatures. Once the cell is stabilized, an appreciable sum of current denseness is observed and it is noted as a map of electromotive force at the applied temperature.
The information in Fig. 6 and 7. indicate that the addition in the current denseness is additive with the cell electromotive force. From the Table 1. It is besides observed that the current denseness is higher in conventional coppice method than I-R method. In I-R method, the maximal current denseness observed is 1.35 A/cm2 at a cell electromotive force of 2.0 V at 80 oC for SPEEK-TPA-ZrO2 membrane. And the production of H is 1.9 L/hr. SPEEK-TPA-ZrO2 composite membrane showed near comparable public presentation to Nafion® 117, due to high proton conduction every bit good as on IEC values. Furthermore, the add-on of tungstophosphoric acid and Zr oxide in the SPEEK polymer organic matrix enabled the readying of composite membranes with a broad scope of belongingss refering proton conduction, H2O consumption and IEC values. Therefore, these membranes can be used in the hereafter to do a critical rating of the relationship between the proton electrolyte membrane belongingss and the H2O electrolysis public presentation.
The current denseness versus electromotive force curve of the SPEEK/TPA/ZrO2 membrane in the H2O electrolysis cell reveals the 2nd best public presentation among the five membranes mentioned above, that is, Pt/Nafion117/IrO2, Pt/SPEEK/IrO2, Pt/SPEEK-TPA-TiO2/IrO2, Pt/SPEEK-TPA-SiO2/IrO2 and Pt/SPEEK-TPA-ZrO2/ IrO2.
The difference in the coating processs depends on the accelerator activity, where the best via media between denseness of active sites and electrical conduction was found. High electrical conduction of the accelerators is important in Solid Polymer Electrolyte Membrane electrolysis systems due to the porous design of the current aggregators, where current conveyance must take topographic point in askance way of the catalytic bed besides in perpendicular way. This leads to a longer current way and a lower cross subdivision for negatron conveyance compared to what is obviously found. Therefore, electrical conduction of the accelerators in solid polymer electrolyte membrane electrolysis of foremost luster.
Since Pt-black is well less active towards O development than IrO2. This can likely be explained by an addition in electric conduction of the catalytic bed. The Pt atoms rapidly formed big agglomerates and segregated during the spraying phase. Metallic Pt possess different surface belongingss compared to oxide atoms and interact otherwise with the ink dissolver, It was believed that a pH gradient was produced through the membrane and that dissolved Iridium species precipitated when exceeding its solubility bound at a certain PH. This was explained by the formation of a common d-band and a lowering of the heat of interaction between IrO2 and O where the oxidization to IrO4 was suppressed.
Pt-black operated as a much better H accelerator at higher current densenesss, perchance caused by a more dumbly jammed catalytic bed and a higher electrical conduction.
Similarly IrO2 operated as a much better O accelerator at higher current densenesss and a higher electrical conduction.
The composite membranes were prepared by a straightforward sol-gel method. The electrochemical belongingss, tensile strength, puffiness, and dimensional stableness were found to better with the add-on of fillers and blended with TPA to avoid inordinate H2O swelling and to reenforce their mechanical belongingss. Increasing the local concentration of sulfonic acerb units every bit good as dividing the hydrophilic medieties from the hydrophobic polymer chief concatenation enabled the stabilisation of the morphology of the water-swollen membranes and a publicity of the proton conductivity.
SPEEK-TPA-ZrO2 composite membrane showed near comparable public presentation to Nafion® 117 due to high proton conduction every bit good as on IEC values. There is besides a clear difference between these spectra of dried membranes and wet membranes. Furthermore, the add-on of tungstophosphoric acid and Zr oxide in the SPEEK polymer organic matrix enabled the readying of composite membranes with a broad scope of belongingss refering proton conduction, H2O consumption and IEC values. Based on the above experiments, it can besides be
observed that the surfacing method of conventional coppice surfacing method showed better public presentation than the impregnation decrease method. Hence it is suggested that the coppice coating is the most appropriate method for fixing the accelerator used in PEM electrolysis.