Hydrogen is an alternative to fossil fuels that may represent a cleaner way to power our world. Hydrogen energy involves the use of hydrogen and hydrogen-containing compounds to generate energy to be supplied to all practical uses needed with high energy efficiency, overwhelming environmental and social benefits, as well as economic competitiveness. There are four main sources for the commercial production of hydrogen: natural gas, oil, coal, and electrolysis of water. However, the electrolysis of water through passing electric current is the key technology for carbon free hydrogen production.
By using a source of renewable energy, the electrolysis of water for large-scale hydrogen production is emerging as one of the most promising options in the transition to a carbon-neutral economy. In this process, water is split into hydrogen (H2) and oxygen (O2) under the influence of electricity with zero carbon emissions. This reaction takes place in a unit called an electrolyzer. Based on the types of electrolytes and operating conditions, electrolyzers can be classified into three main categories: alkaline water electrolyzer (AWE), high temperature solid oxide electrolyzer (SOE) and proton exchange membrane(PEM) electrolyzer.
1. Alkaline Water Electrolysis
Alkaline water electrolysis is well established mature technology for industrial hydrogen production up to the multi-megawatt range in commercial applications across the globe. However, they suffer from problems of efficiency and poor start/stop dynamics, making them difficult to couple to renewable energy sources.
2. Solid Oxide Electrolysis
Typically, the solid oxide electrolyzer operates with water in the form of steam at high temperatures (500 °C ~850°C) can drastically reduce the power consumption to split the water into hydrogen and oxygen, consequently increasing the energy efficiency. Due to its insufficient long-term stability, this technology has not be approached for commercialization.
3. Proton Exchange Membrane Water Electrolysis
PEM electrolysis cell is equipped with a solid polymer electrolyte that is responsible for the conduction of protons, separation of the gases, and electrical insulation of the electrodes. It operates at lower temperatures with higher current densities, and is safer than alkaline water electrolysis due to the absence of caustic electrolytes and smaller footprint.
Generally, the overall reaction of water electrolysis can be divided into two half-cell reactions: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). HER is the reaction where water is reduced at the cathode to produce H2, and OER is the reaction where water is oxidized at the anode to produce O2.
Anode Reaction: H2O → ½ O2 + 2H+ + 2e–
Cathode Reaction: 2H+ + 2e– → H2
Total Reaction: H2O → H2 + ½ O2
One of the critical barriers that keep water splitting from being of practical use is the sluggish reaction kinetics of OER and HER due to high overpotentials, a measure of the kinetic energy barriers. Therefore, catalysis plays a major role in both OER and HER. Highly effective catalysts are required to minimize the overpotentials for OER and HER towards efficient H2 and O2 production.
Our platinum/iridium catalyst coated anodes and cathodes are presently recognized as the top electrode materials in PEM electrolyzers, which exhibit acceptable electrochemical activity and optimizing life in acidic electrolytes.
