Hydrogen Production

by Electrolysis

Agata Godula-Jopek

• Publisher: Wiley-VCH
• Year: 2015
• Print ISBN: 9783527333424
• eBook ISBN: 9783527676521
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

Covering the various aspects of this fast-evolving field, this comprehensive book includes the fundamentals and a comparison of current applications, while focusing on the latest, novel achievements and future directions.
The introductory chapters explore the thermodynamic and electrochemical processes to better understand how electrolysis cells work, and how these can be combined to build large electrolysis modules. The book then goes on to discuss the electrolysis process and the characteristics, advantages, drawbacks, and challenges of the main existing electrolysis technologies. Current manufacturers and the main features of commercially available electrolyzers are extensively reviewed. The final chapters then present the possible configurations for integrating water electrolysis units with renewable energy sources in both autonomous and grid-connected systems, and comment on some relevant demonstration projects.
Written by an internationally renowned team from academia and industry, the result is an invaluable review of the field and a discussion of known limitations and future perspectives.

Chapter 1
Introduction

Agata Godula-Jopek

We find ourselves on the cusp of a new epoch in history, where every possibility is still an option. Hydrogen, the very stuff of the stars and our own sun, is now being seized by human ingenuity and harnessed for human ends. Charting the right course at the very beginning of the journey is essential if we are to make the great promise of a hydrogen age a viable reality for our children and a worthy legacy for the generations that will come after us.

Jeremy Rifkin [1].

Hydrogen is being considered as an important future energy carrier, which means it can store and deliver energy in a usable form. At standard temperature and pressure (0 °C and 1013 hPa), hydrogen exists in a gaseous form. It is odourless, colourless, tasteless, non-toxic and lighter than air. The stoichiometric fraction of hydrogen in air is 29.53 vol%. Abundant on earth as an element, hydrogen is present everywhere, being the simplest element in the universe representing 75 wt% or 90 vol% of all matter. As an energy carrier, hydrogen is not an energy source itself; it can only be produced from other sources of energy, such as fossil fuels, renewable sources or nuclear power by different energy conversion processes. Exothermic combustion reaction with oxygen forms water (heat of combustion 1.4 × 10⁸ J kg⁻¹) and no greenhouse gases containing carbon are emitted to the atmosphere.

Selected physical properties of hydrogen based on Van Nostrand are presented in Table 1.1 [2].

Table 1.1 Selected physical properties of hydrogen.

Parameter	Value	Unit
Molecular weight	2.016	Mol
Melting point	13.96	K
Boiling point (at 1 atm)	14.0	K
Density solid at 4.2 K	0.089	g cm^−3
Density liquid at 20.4 K	0.071	g cm^−3
Gas density (at 0 °C and 1 atm)	0.0899	g l^−1
Gas thermal conductivity (at 25 °C)	0.00044	cal·cm s^−1 cm^−2 °C^−1
Gas viscosity (at 25 °C and 1 atm)	0.0089	cP
Gross heat of combustion (at 25 °C and 1 atm)	265.0339	kJ g^−1 mol^−1
Net heat of combustion (at 25 °C and 1 atm)	241.9292	kJ g^−1 mol^−1
Autoignition temperature	858	K
Flammability limit in oxygen	4–94	%
Flammability limit in air	4–74	%

Source: By permission of Wiley VCH.

The energy content of hydrogen is 33.3 kWh kg⁻¹, corresponding to 120 MJ kg⁻¹ (lower heating value, LHV), and 39.4 kWh kg⁻¹, corresponding to 142 MJ kg⁻¹ (upper heating value, UHV). The difference between the UHV and the LHV is the molar enthalpy of vaporization of water, which is 44.01 kJ mol⁻¹. UHV is obtained when as a result of hydrogen combustion water steam is produced, whereas LHV is obtained when the product water is condensed back to liquid.

Because of its high energy-to-weight ratio, hydrogen has commonly been used in a number of applications for the last 100 years and a lot of experience has been gained since its production and use, with it becoming the fuel of choice. Hydrogen application for transportation has a long history. One of the first demonstrated applications took place in the eighteenth century in Paris. The first manned flight (Jacques Charles and Nicolas Robert) had been demonstrated in a balloon called “hydrogen gas aerostat” for about 45 min, covering a distance of about 21 km.

A car with an internal combustion engine (ICE) that used a mixture of hydrogen and oxygen for fuel was invented by Francoise Isaac de Rivaz from Switzerland in January 1807 and it was the first internal combustion-powered automobile. The main application of hydrogen in the twentieth cent...

Table of contents

• Cover
• Related Titles
• Title Page
• Copyright
• Foreword
• Preface
• List of Contributors
• Chapter 1: Introduction
• Chapter 2: Fundamentals of Water Electrolysis
• Chapter 3: PEM Water Electrolysis
• Chapter 4: Alkaline Water Electrolysis
• Chapter 5: Unitized Regenerative Systems
• Chapter 6: High-Temperature Steam Electrolysis
• Chapter 7: Hydrogen Storage Options Including Constraints and Challenges
• Chapter 8: Hydrogen: A Storage Means for Renewable Energies
• Chapter 9: Outlook and Summary
• Index
• End User License Agreement