Harnessing the Power of Water Splitting: From Theory to Commercial Applications

Introduction to Electrochemistry

Electrochemistry, the branch of chemistry that deals with the relationship between electrical energy and chemical reactions, plays a crucial role in numerous modern technologies. At its core, electrochemistry involves reactions at the interface of an electrode and an electrolyte, where voltage and current drive the processes. Key components include:

• Anode: The electrode where oxidation occurs.
• Cathode: The electrode where reduction occurs.
• Electrolyte: The medium that allows the movement of ions between the anode and cathode.

Electrochemical reactions are governed by kinetics (the rate of reaction) and thermodynamics (the feasibility of a reaction), both of which are crucial for designing efficient electrochemical cells.

Theory of Water Splitting

Water splitting is a fundamental electrochemical process that converts water (H?O) into oxygen (O?) and hydrogen (H?) gases. This process involves the following reactions (acidic conditions):

• At the anode (oxidation):

• At the cathode (reduction):

Thermodynamics: The Gibbs free energy change (ΔG) for the overall water-splitting reaction is positive, indicating that the process requires energy input. This energy is typically supplied in the form of electrical energy plus a little heat.

Reaction Kinetics: The efficiency of water splitting depends on the kinetics of the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode. Catalysts are often used to lower the activation energy and increase the reaction rate.

Cell Design: Water-splitting cells can vary in design, but they generally consist of an anode and a cathode immersed in an electrolyte. Types of cells include:

• Alkaline Water Electrolyzers: Use an alkaline electrolyte like potassium hydroxide (KOH).
• Proton Exchange Membrane (PEM) Electrolyzers: Use a solid polymer electrolyte.
• Solid Oxide Electrolyzers (SOE): Operate at high temperatures using a ceramic electrolyte.

Commercial Applications

The practical implications of water splitting are vast, especially in the context of sustainable energy and industrial processes:

• Hydrogen Production: Hydrogen produced via water splitting can be used as a clean fuel in fuel cells, generating electricity with water as the only by-product.
• Industrial Chemicals: Hydrogen is a key feedstock in the production of ammonia for fertilisers, methanol, foods, and pharmaceuticals.
• Energy Storage: Water splitting allows for the storage of renewable energy in the form of hydrogen, which can be converted back into electricity when needed.

Summary

Water splitting represents a promising pathway towards sustainable energy solutions and industrial applications, especially in the hard-to-abate sectors. Understanding the principles of electrochemistry, from reaction kinetics to cell design, is essential for optimising this process. As technology advances, the commercial viability of water splitting will continue to improve, driving progress toward a cleaner, more efficient future.

References

• O'Hayre et.al, Fuel Cell Fundamentals, 2nd Edition, Wiley
• P. Atkins, L. Jones, Chemical Principles- The Quest for Insight, 3rd Edition, W.H Freeman & Co.
• Green hydrogen economy - predicted development of tomorrow: PwC