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

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1 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, power, etc., due to this a drastic increase in usage of fossil fuels has led to tremendous demand of energy. As the fossil fuels are limited, there is a need for an alternative source which is efficient, reproducible, applicable, recyclable and byproduct shall be free from CO2 emissions. Hydrogen can be one such reliable alternative for all our energy needs, however it cannot be considered as an energy source as it doesn t occur in nature (elemental or molecular form). The most abundant source of hydrogen is water, Electrolysis of water can be good choice to produce hydrogen. According to the laws of thermodynamics, energy spent for splitting of water is higher than energy released from hydrogen (produced) [Frano Barbir et al., 2005; Lirong Ma et al., 2009]. Over past decades research has proven that hydrogen can be used in day to day applications. Today the world produces over 500 billion m 3 year -1 (42 million tons year -1 ) of Hydrogen; Most of the technologies (over 95%) use fossil fuels and natural gas to produce hydrogen [S.P.S.Badwal et al., 2006; Isabel Navarro-Solıs et al., 2010]. The hydrogen utilization by the industry has been given in Table 1.1.

2 2 Table 1.1 Hydrogen utilization S No Industry Hydrogen utilization (%) Purpose 1 Fertilizer Over 50% Ammonia production 2 Oil Over 33% Removal of Impurities, upgrading heavy oil fractions etc., 3 Chemical and metallurgical Nearly 17% Methanol production, for metallurgy processes and other applications The utilization of hydrogen has been limited, because of high cost of production, lack of transport, storage and distribution infrastructure. 1.2 Hydrogen production There are various methods available for production of hydrogen such as biological, photoelectrochemical, thermochemical, and electrochemical methods. The only practical way to produce hydrogen using renewable energy sources is by water electrolysis [P.Kruger, 2000] Biological technology Biological hydrogen production technology is based on the use of microorganisms to produce hydrogen. This kind of technology involves dark-fermentation, photo-fermentation and biophotolysis. The rate of hydrogen production is relatively slow and varies from organism to organism based on its metabolic activity [D.Sivaramakrishna et al., 2009].

3 Photoelectrochemical technology Photoelectrochemical hydrogen production is a one step process of splitting water by illuminating a water-immersed semiconductor with sunlight. [S.P.S.Badwal et al., 2006]. Major challenges for this technology are Poor matching of the semiconductor band gap with the solar spectra. Instability of the semiconductor materials in the aqueous phase. Difference between the semiconductor band edges and the electrochemical reactions. Poor kinetics of the Hydrogen generation reaction Thermochemical method Steam reforming method is the most widely used to produce hydrogen from natural gas, coal, methanol (CH 3OH), ethanol (C 2H 5OH) and other hydrocarbons. For this kind of process catalysts are used to convert raw materials to hydrogen. Gasification and pyrolysis are also used for hydrogen production, where the process involves high temperature operation and the usage of feed stocks such as coal, wood, other biomass and heavy or residual oils. This process contributes 50% of hydrogen production all over the world Electrochemical technology Electrolysis of water is the best known technology till today to produce hydrogen. The efficiency of this process is in the range of 60 70%. In case of commercial electrolysers the overall efficiency will drop down

4 4 to 25%. To produce 1 kg of hydrogen (standard electrolyser conditions) kwh of electricity is required. The cost of electricity directly contributes to high production costs [Agus Haryanto et al., 2005]. 1.3 Importance of Proton exchange membrane water electrolysis Proton exchange membrane (PEM) water electrolysis system offers several advantages over traditional technologies like greater energy efficiency, higher production rates, and more compact design [A.Marshall et al., 2007]. The main components for the PEM electrolyser are PEM, electrocatalysts (mostly noble metals are used), current collectors and end plates. The PEM water electrolysis process ensures high current density and safe operation when compared with conventional electrolysis process [S.Sawada et al., 2008; Pyoungho Choi et al., 2004]. The advantages and challenges of the above process are given below Advantages Greater energy efficiency High pure hydrogen gas Flexible hydrogen production at wide and higher current densities and high voltage efficiency Small scale hydrogen supply is simple Safe and compact design (No liquid electrolyte circulating) By product is pure oxygen Best solution for renewable energy storage

5 5 Easily scalable to large scale production Challenges High operation costs Hydrogen storage for energy supplies High cost of electrocatalysts Expensive technologies The polymer electrolyte membrane or proton exchange membrane (PEM) is a solid polymer electrolyte membrane used as electrolyte for fuel cells and water electrolysers. The PEM conducts protons from one electrode to another. The most commonly used PEM membrane is Nafion (manufactured by DuPont, USA). Efficiencies of PEMs are in the range of 40 60% higher heating value of hydrogen (HHV) [P.Millet et al., 2010]. In most of cases noble metals and their oxides such as Platinum (Pt), Palladium (Pd), Ruthenium (Ru), Iridium (Ir), Rhodium (Rh) etc., are used as electrocatalysts for this process, due to their resistance towards corrosion in acidic media. As the availability of the noble metals is limited, Hence noble metals supported on carbon can reduce the usage of noble metals. The precursors of the noble metals are chemically deposited on the surface of the carbon support for using as electrocatalyst. [Grigoriev. S et al., 2006; A.T.Marshall et al., 2007; Kunchan Lee et al., 2006]. Carbon support plays a vital role in the performance of the catalyst, and provides structural, conductive and durable support for the active

6 6 metal particles. It has a strong corrosion resistance, high surface area, excellent crystallinity, good dispersion, low density and good electrical conductivity. Carbons like activated carbon (AC), carbon black (CB), carbon nanomaterials (CNMs) are currently considered as the catalyst support because of their long life. CNMs can be produced by various methods like chemical vapor deposition (CVD), flame spray pyrolysis, electric arc and laser etc., [Yu Li et al., 2004; Giuseppe Gulino et al., 2005; Ting-Chi Liu et al., 2006]. AC and CB have particle diameters in the range of 5 30 µm and surface area of in the range of m 2 g -1, while CNMs have diameters in the range of nm are madeup of hexagonal lattices of carbon and surface area in the range of m 2 g -1 [D.Sebastian et al., 2010]. Electrocatalyst preparation methods Impregnation-reduction method [Kunchan Lee (2006)] Pd precursors and precipitation method [Grigoriev S (2006)] Sulphite method [Siracusano S, 2010] Bonnemann s Method [H.Bonnemann, 1991] Adams s method [Adams R, 1923] The Prepared electrocatalysts are coated on the either side of the PEM and made as a membrane electrode assembly and tested in PEM cell [A.T.Marshall et al., 2007; J.Moreira et al., 2004]. 1.4 Importance of this study The development of the PEM water electrolyser is in its nascent stages, worldwide many researchers are trying to develop efficient

7 7 reliable and cost effective PEM electrolyser systems. In India, a very few national laboratories, Institutes of national importance are working in the area of PEM water electrolysers. 1. Centre for Electrochemical Research Institute, Karaikudi 2. Naval Minerals Research Laboratory, Mumbai 3. Centre for Fuel cell Technology, ARCI, Chennai 4. IIT Delhi, New Delhi 5. Mahindra and Mahindra Group As this technology is limited to R&D there is a need to develop more and more reliable, cost effective technology for boosting hydrogen economy in our country. 1.5 Scope of the research work The present study aims to study the performance of Palladium for the Hydrogen evolution reaction (HER) in PEM water electrolysis cells by using different types of carbon as support. Palladium, which is widespread in the Earth crust and less expensive than platinum, also exhibits interesting electrocatalytic properties for various reduction and oxidation electrode processes [S.A.Grigoriev, 2008]. Pd nanoparticles, electrochemically deposited onto Carbon support have been reported to exhibit a high electrochemical activity. Concerning water electrolysis applications, the possibility of using Pd (dispersed onto carbon electrodes) for the HER in alkaline medium has been reported by [E.Ndzebet et al., 1995]. But for PEM water electrolysis and the HER in acidic media, palladium has been less studied than

8 8 platinum. Pd supported on AC, CB and CNMs has been prepared by using chemical reduction method taking PdCl 2 as precursor and employing polyol method [Grigoriev S et al., 2006]. The Pd/C has been used as cathode for HER and RuO 2 has been used as Anode for Oxygen evolution reaction (OER). The prepared electrocatalysts are sprayed on respective sides of pretreated Nafion 115 membrane and made as Membrane electrode assemblies (MEAs) of area 10 cm 2 and 50 cm 2. Pd/C (AC, CB and CNMs) has been prepared in different weight percentages such as 5wt%, 10wt%, 20wt% and 30wt%. Thus prepared MEAs are tested in inhouse fabricated 10 cm 2 area single cell, 50 cm 2 double and five cell stacks. The performances of the prepared MEAs are tested in PEM water electrolyser and have been reported and discussed. Aims and objectives 1. Design and fabrication of 10 cm 2 area single cell, 50 cm 2 area double and five cells stack assembly for PEM water electrolyser. 2. Synthesis of carbon nanomaterials using chemical vapour deposition method. 3. Preparation of Pd/C electrocatalysts using chemical reduction method and Characterization using SEM, EDS, BET, ICP, XRD and Cyclic voltammetry. 4. Fabrication of Membrane electrode assemblies (MEA) using Nafion 115 membrane.

9 9 5. Testing of prepared MEAs in designed 10 cm 2 and 50 cm 2 area PEM cells. 6. Design and fabrication of prototype PEM water electrolyser of higher capacity.