10 Chapter 2 K. NAGA MAHESH Review of Literature. The process of water electrolysis dates back to 1789 when the

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1 10 CHAPTER 2 REVIEW OF LITERATURE 2.1 Introduction The process of water electrolysis dates back to 1789 when the merchant Adriaan Paets van Trootswijk and medical doctor Johan Rudolph in Amsterdam, found that water could be split into hydrogen and oxygen gas by application of electric power. This is the first discovery of water electrolysis process in the history. After that Nicholas and Carlisle (1800) brought into the public [R.de Levie et al., 1999]. In 1839, Sir William Groove worked on water electrolysis and discovered the corresponding process that hydrogen together with oxygen is able to generate electric power and one of the first primitive fuel cells have been developed [J.A.A.Ketelaar et al., 1993]. Based on above developments 400 industrial electrolysers are setup and in operation by the year 1902 [W.Kreuter et al., 1996]. The first alkaline fuel cell has been successfully demonstrated by F.T.Bacon in early 1930s [J.A.A.Ketelaar et al., 1993]. Grubb (1959) described polymer membrane fuel cell and in 1966 the General electric company has developed first electrolyser based on PEM for space applications [W.Kreuter et al., 1996; M.Rikukawa, 2000]. Later in 1984, Hamilton Sunstrand (a subsidiary of United Technologies Corporation) has developed SPE electrolysers. These days very few companies are producing commercial

2 11 electrolysers. The most important aspect in the development of electrolysers are PEM membrane and electrocatalyst, the researchers are looking for low cost, non-noble electrocatalysts for PEM electrolysis processes. However, catalyst development activity is significantly progressing. 2.2 PEM water electrolysis Guobao Chen et al., (2008) operated the PEM water electrolyser at 80 C and at 1 bar pressure. Nafion 115 has been used as membrane, Pt/C (2.1 mg cm -2 ) and IrO2 (loading of 0.9 mg cm -2 ) has been used as cathode and anode respectively. S.A.Grigoriev et al., (2008) Pt 40/Vulcan XC72, Pd 40/Vulcan XC72 (cathode) with loading 0.7 mg cm -2 and IrO 2 (anode) with loading of mg cm -2 has been tested in 7 cm 2 and 25 cm 2 area PEM water electrolyser and operated at 90 C. A.Marshall et al., (2007) have used Nafion 115 as electrolyte membrane. 20wt% Pt/C (cathode), IrO 2 (anode), Ir 0.7Ta 0.3O 2 (anode) and IrO.6Ru0.4O2 (anode) has been used as electrocatalysts. The PEM water electrolyser has been operated at 1 bar pressure and 80 C. The lowest possible voltage is 1.56V has been reported. S.P.S.Badwal et al., (2006) have reported development of PEM water electrolyser system for producing high pure oxygen. The electrolyser has been operated at 2 bar pressure and C. Nafion 112 and 115 membranes have been used as electrolyte, Pt/C (loading

3 12 of 0.4 mg cm -2 ) and noble metal ( mg cm -2 ) are used as cathode and anode respectively with electrode area of cm 2. V.Antonucci et al., (2008) Nafion SiO2 composite membrane has been compared with Nafion 115 in PEM water electrolyser. Pt/Vulcan XC72 (0.1 mg cm -2 ) and IrO 2 (0.2 mg cm -2 ) has been used as cathode and anode. The electrolyser has been operated in temperature range of C and at 1 3 bar pressure. The Nafion- SiO 2 composite membrane has shown good performance at current density of A cm -2 at voltage of 1.9V. S.Giddey et al., (2010) have used Nafion 115 membrane along with Pt (cathode) and Ir (anode) electrocatalysts coated on it with electrode area cm 2 and operated the electrolyser at 20 bar pressure and at temperature C. The Hotpress conditions for the making MEAs has been show in section 2.3.

4 Hotpress conditions for making MEAs S No Mode Membrane Cathode/ Anode MEA area (cm 2 ) Temp ( C) Pressur e (bar) Time of Press ( in sec) Reference 1 EL Nafion 115 Cathode: 40wt% Pt/C (0.4 mg cm -2 ) A.T.Marshall et al., 2007 Anode: IrxRuyTazO2 (2 mg cm -2 ) 2 FC Nafion Abhishek Guha et al., FC Nafion 115 PdxPty/C, PdxPtyRuz/C, Amanda C. Garcia, et al., (anode) 2008 Pt/C (anode and cathode) 4 FC Nafion wt% Pt/Vulcan XC Apichai Therdthianwong, et al., FC Nafion wt% Pt/C, 20wt% Pt/C, Balaji Krishnamurthy et Pt black al., 2009

5 Hotpress conditions for making MEAs S No Mode Membrane Cathode/ Anode MEA area (cm 2 ) Temp ( C) Pressur e (bar) Time of Press ( in sec) Reference 6 FC Nafion Chien-Ming Lai, et al., EL Nafion E.Slavcheva et al., FC/ Nafion 115 Cathode: Grigoriev.S et al., 2006 EL Pd/Vulcan XC72 Pt/Vulcan XC72 (0.3 mg cm - 2 ) Anode: IrO2 (0.3 mg cm -2 ) 9 FC Nafion 115 Cathode: 2wt% and 4wt% J.Moreira et al., 2004 Pd/Vulcan and Pd/C Loading: 1 mg cm -2 Anode: 10wt% Pt/Vulcan Loading: 0.4 mg cm EL Nafion Anode: Ir0.4Ru0.6O Jinbin Cheng et al., 2009

6 Hotpress conditions for making MEAs S No Mode Membrane Cathode/ Anode MEA area (cm 2 ) Temp ( C) Pressur e (bar) Time of Press ( in sec) Reference 1035 Loading: 1 mg cm -2 Cathode: Pt/C, RuO2/C, and IrO2/C Loading: 0.5 mg cm Nafion wt% Pt/Carbon black (0.4 mg cm -2 ) Liangliang Sun, et al., FC Nafion 1035 Anode: Pt/C (0.25 mg cm -2 ) Cathode: Pt/C (0.5 mg cm -2 ) 13 FC Nafion 115 Anode: 30 wt% Pt-Ru/C (3.0 mg cm -2 ) Cathode: 40 wt% Pt/C N.Rajalakshmi et al., Peng Liu, et al., 2010

7 Hotpress conditions for making MEAs S No Mode Membrane Cathode/ Anode MEA area (cm 2 ) Temp ( C) Pressur e (bar) Time of Press ( in sec) Reference (2.0 mg cm -2 ) 14 EL Nafion wt% Pt/C (anode and cathode) (0.66 mg cm -2 (anode) and 0.70 mg cm -2 (cathode)) PremKumar Sivasubramanian, et al., FC Nafion 112 Pt/C Raimundo R. Passos et & 1135 Loading: al., mg cm FC Nafion 1135 Pt/Vulcan XC72 Pd/Vulcan XC72 (0.35 mg cm -2 ) S.A.Grigoriev et al., EL Nafion wt% Pt/C (0.2 mg cm -2 ) S.Giddey, et al., EL Nafion 112 Cathode: Pt/C Shidong Song, et al., 2008

8 Hotpress conditions for making MEAs S No Mode Membrane Cathode/ Anode MEA area (cm 2 ) Temp ( C) Pressur e (bar) Time of Press ( in sec) Reference 0.5 mg cm -2 ) Anode: Ru, Ir, RuO2, IrO2, Ru0.5Ir0.5O2 (3 mg cm -2 ) 19 URFC Nafion Pt black, PtIr, PtIrOx, PtRu 1135 (4.0 mg cm -2 ) 20 URFC Nafion 115 Cathode: Pt black Anode: Pt/IrO2 21 URFC Nafion 115 Cathode: Pt black Anode: IrO 2 Loading: 2 4 mg Sung-DaeYim et al., T.Ioroi et al., Tsutomu Ioroi et al., 2002 cm URFC Nafion 117 Cathode: Pt black (2 mg cm -2 ) Anode: Ir black (2 mg cm -2 ) U.Wittstadt et al., 2005

9 Electrocatalysts and characterization Fenglei Li et al., (1997) have reported volumetric behavior of a chloride complex of palladium, and characterized by CV, XPS. Cyclic voltammetry is performed by using a conventional three electrode electrochemical system with glassy carbon (GC) as working electrode, Platinum foil as counter electrode and saturated calomel electrode (SCE) as reference electrode and a double salt bridge with a solution of saturated NH4NO3 is used to prevent from the influence of Cl -. A significant cathodic current arises up around 0.0V at the initial cycle and is attributed to reduction of the electrode surface complexes of palladium in 0.3M H 2S0 4 solution and potential from -0.4 to +1.0V. With the subsequent potential scanning, the cyclic voltammograms reach a steady-state and the electrode surface complexes of palladium had been almost completely transformed to PdO. Highly dispersed Pd particles can be obtained when the surface complexes are reduced electrochemically to Pd atoms. The Pd particles obtained in this way are in nanometer scale and exhibit high catalytic activity towards the oxidation of hydrazine. Feng Ye et al., (2010) Pt IrO2, Ti/Pt IrO2, Ti/IrO2 electrocatalysts are prepared using the dip-coating/calcinations method on titanium substrates for investigated for oxygen evolution. It has been found that incorporation of Pt into IrO 2, not only increased the conductivity significantly but also produced some synergic effect

10 19 to make Pt IrO2 electrocatalyst much more stable and decreased the flat band potential of IrO2. The electrocatalytic activity for oxygen evolution has been enhanced. R. Pattabiraman (1997) has studied palladium on different carbon support (activated carbon and Vulcan XC72) using chemical reduction method. The prepared electrocatalyst are characterized by XRD for morphology and electrochemical surface area by using cyclic Voltammetry. Pd dispersed catalysts on carbon support shown high electrochemical activity for the oxidation of hydrogen, methanol, formaldehyde and ethylene glycol is evaluated in alkaline solutions. The electrochemical activity is dependent upon the crystallite properties like surface area, dispersion and crystallite size, the results indicate that the activity can be increased by alloying with other elements. S.A.Grigoriev et al., (2008) synthesized electrochemically characterized carbon-supported Pt and Pd nanoparticles (CSNs) for PEM water electrolysers. Pt and Pd nanoparticles are deposited on the surface of Vulcan XC-72 by chemical reduction of Pd and Pt salts using ethylene glycol and formaldehyde as reductant. The prepared electrocatalyst are made as MEAs and tested in 7 cm 2 area electrolysis test cell at 90 C and 1 atm pressure. The electrocatalysts are characterized using BET surface area, cyclic Voltammetry and TEM. The prepared MEAs have demonstrated good performance in 7 cm 2

11 20 area single cells with overall efficiencies of 88% at 1 A cm 2. Pd can be considered as an alternative catalyst to Pt in respect to the HER in PEM water electrolysis cells. Liangliang Sun et al., (2009), have developed a new improved fabrication technique for preparation of catalyst-coated membrane (CCM) using a conventional hotpress method and a hot sprayed membrane method. The prepared CCMs are evaluated using I V polarization, cyclic voltammetry and electrochemical impedance spectroscopy. The results indicate that the CCM fabricated by direct spraying catalyst ink has exhibited a good performance than a conventionally prepared one. Feng Ping Hu et al., (2008) reported for the first time preparation of hollow carbon spheres of ultrahigh surface with open micropores and nanochannels using hydrothermal and intermittent microwave heating (IMH) methods, with BET surface area of m 2 g 1. Pd/HCS has shown thrice the activity of Pd/Vulcan XC-72 carbon. S.I.Pyun et al., (1996) studied hydrogen evolution reaction (HER) on 10wt% Pd/C electrode, Pd foil and vulcan XC72 in 0.1M NaOH solution. The resulted cyclic voltammograms and AC impedance suggests the HER will takes place along with the absorption and diffusion of hydrogen above on -1.10V (Pd/C), -0.96V (Pd foil) and V (Vulcan XC72) vs SCE. The hydrogen evolution overpotential on

12 21 the Pd/C electrode is decreased by 0.10V in comparison to the carbon electrode due to the larger electrochemical active area of the finely dispersed Pd particles. J.J.Salvador-Pascual et al., (2007) have studied the kinetics of oxygen reduction reaction (ORR) using synthesized Palladium electrocatalyst powder by chemical reduction method using PdCl 2 precursor with NaBH 4 in a THF solution at 0 C. The prepared electrocatalysts are characterized by XRD, SEM, and AFM techniques. Results show the formation of nanocrystalline fcc hexagonal palladium (4 nm average size) and the effect of temperature on electrochemical parameters are proportional to the temperature with the transfer coefficient α, and the electrode kinetics reveals that the enthalpy turnover of the ORR may play a significant role. Palladium nanoparticles show a poorly catalytic activity in relation to Pt and Ru electrocatalysts in the acid media. S.A.Grigoriev et al., (2008) reported synthesis of carbon support nanophase Pd and Pt electrocatalysts using ethylene glycol and formaldehyde reduction method for hydrogen oxidation in proton exchange membrane (PEM) fuel cells. The prepared electrocatalysts are characterized by cyclic voltammetry. Some decrease in electrochemical active surface of Pd based catalysts in comparison to that of Pt-based catalysts has been reported. Over all, the electrical performances of fuel cells with Pd catalysts are smaller than Pt

13 22 catalysts. The results obtained show that the simultaneous sorption/reduction method is a promising way for the preparation of electrocatalysts for fuel cell applications. Thus, the present study demonstrates the principal possibility of replacement of Pt by Pd in the hydrogen electrode of PEM fuel cell. N.Rajalakshmi et al., (2005) synthesized Pt/CNTs electrocatalyst by using chemical reduction method and tested in PEM fuel cells. The CNTs are synthesized using CVD and pretreated with HNO3 solution. The prepared Pt/CNTs electrocatalyts are characterized by SEM, TEM, XPS, cyclic voltammetry. Electrodes prepared with CNTs with 19.6% Pt loading shown a higher performance. CNTs have to be functionalized to have a uniform dispersion with a narrow Pt particle range, rather than a higher loading of platinum. S.A.Grigoriev et al., (2011) reported preparation of Platinum and palladium nano-particles supported by graphitic nano-fibers (GNFs) for hydrogen evolution reaction (HER) in PEM water electrolysers. Raw GNF structures have been synthesized by chemical vapor deposition (CVD). Pt and Pd nanoparticles have been deposited on GNFs using impregnation reduction methods. The prepared Electrocatalysts are characterized by using TEM analysis and cyclic voltammetry. The results imply that GNF supported Pt catalyst exhibits a slightly enhanced electrochemical activity with regard to the

14 23 hydrogen evolution reaction than Pt/XC-72. PtPd/GNF has exhibited similar performances as Pt/XC-72. Pd can be a good alternative for replacement of Pt. P.P.Wells et al., (2009) reported the controlled surface modification procedure for the preparation of Pd/C and Pt/C catalysts modified with Pt and Pd, respectively. The XRD data therefore suggest that there is greater mixing of the Pt and Pd in the Pt/Pd/C system compared to that of Pd/Pt/C. The cyclic voltammograms and EXAFS analysis show that the surface is a mixture of both Pt and Pd. However, strong Pt characteristics are exhibited in the voltammetry of Pt/Pd/C catalysts, most notably a large increase in the stability with respect to the electrochemical environment compared to Pd alone. Anusorn Kongkanand et al., (2006) have prepared Pt/SWNT and enhanced the electrocatalytic activity in comparison to commercial available Pt/carbon black electrocatalyst oxygen reduction reaction (ORR). Pt/SWCNT films have been evaluated using a thin film rotating disk electrode at elevated temperature. Pt deposited on SWCNT exhibited a 2-fold higher rate constant, kapp, than Pt/C. The high porosity of SWCNT facilitates diffusion of the reactant and facilitates interaction with the Pt surface. It is evident from the accelerated durability tests that SWCNT enhance the stability of the electrocatalyst. Furthermore, the lower energy of CO adsorption

15 24 observed with the Pt/SWCNT electrode also demonstrates the COtolerance Electrocatalyst. M.Chen et al., (2010) reported synthesis of Pd/C Electrocatalyst by modified polyol process and its performance has been compared with Pd/C catalyst prepared using NaBH 4 as a reducing agent. The Pd/C catalyst prepared by modified polyol process has shown a higher electrocatalytic activity and stability for formic acid electrooxidation in comparison to the Pd/C prepared by NaBH 4 method, due to the particle size effect, and its peak current density in cyclic voltammetry and current in chronoamperometric curve has reachede 33.2 and 11.2 ma cm 2 at 1,000s. J.Moreira et al., (2004) reported the performance of 2 wt% and 4 wt% Pd/C and Pd/Vulcan catalysts. The electrocatalyst are synthesized by the impregnation method, from Pd (II) acetyl acetonate (aldrich, 99%) precursor. The catalysts are characterized by XRD, AAS, cyclic and linear sweep voltammetry. The results imply that Pd supported on vulcan possesses better oxygen electroreduction characteristics and performed better than Pd supported on C as the cathode electrode. Hongchao Ma et al., (2006) have studied oxygen evolution reaction using RuO2 as anode electrocatalyst for PEM water electrolyser application. The RuO2 catalyst is prepared by a pyrolysis process in a nitrate melt at 300 C and then calcined at different

16 25 temperatures from 350 to 550 C. The physio-chemical properties of RuO2 catalysts have been examined by XRD, FE-SEM, CV, EIS, BET, etc. The impedance results in oxygen evolution region clearly show that the electrocatalytic activity of RuO 2 material decreases with the increase of calcining temperature. The resistance of catalyst layer (R f), however, decreases with increase of calcining temperature, Thus at optimum temperature of calcination has been found to be 350 C. Furthermore, the RuO 2 anode also displays better stability at higher current density (1.1 A cm 2 ) in the PEM based electrolysers. Summary The review of literature provides the brief summary of the research done till date. Worldwide most of the researchers have used Pt based electrocatalysts for Hydrogen electrode in PEM fuel cell and water electrolyser applications. Palladium, which is widespread in the Earth crust and less expensive than platinum, exhibits interesting electrocatalytic properties for various reduction and oxidation electrode processes, has less extensively studied for this kind of application. Carbon-supported palladium is an interesting material, often used because of carbon high surface area and chemical inertness, particularly in strong basic and acid environments. Hence Pd/C has been selected for using as Hydrogen electrode in PEM water electrolyser application.

1 Chapter 1 K. NAGA MAHESH Introduction. Energy is the most essential and vital entity to survive on this Planet.

1 Chapter 1 K. NAGA MAHESH Introduction. Energy is the most essential and vital entity to survive on this Planet. 1 1.1 Hydrogen energy CHAPTER 1 INTRODUCTION Energy is the most essential and vital entity to survive on this Planet. From past few decades majority of the mankind depend on fossil fuels for transportation,