How Hydrogen is Made From Fossil Fuels
Currently, hydrogen is sourced nearly entirely from fossil fuels. Methane accounts for around 76% of hydrogen production, with coal contributing the remaining 24%. Annually, the global production of hydrogen from fossil fuels reaches an estimated 70 billion kilograms.
Steam methane reforming (SMR) supplies the majority of the world’s hydrogen and approximately 95% of the hydrogen in the United States. Utilizing natural gas as a feedstock, in SMR, methane undergoes a reaction with steam under high temperatures and pressure to generate hydrogen along with carbon monoxide.
Another method of hydrogen extraction involves coal gasification, a process where coal is subjected to high heat and blown through oxygen and steam. The product, a gas known as synthesis gas or syngas, is a mix of hydrogen and carbon monoxide. The process can be expanded by introducing more water, causing the water-gas shift reaction (WGSR), which will produce additional hydrogen and carbon dioxide.
How Renewable Hydrogen is Made
Hydrogen can also be generated through electrolysis, a process that deploys an electric current to drive a chemical reaction. Through electrolysis, water breaks down into hydrogen and oxygen. In order for hydrogen production to be considered renewable, three essential components are required: an electrolyzer, water, and a renewable energy source. (In the reverse process, occurring in fuel cells, hydrogen combines with oxygen to generate water and electricity.) Currently, the utilization of electrolysis encompasses three types of technologies: alkaline, proton exchange membrane, and solid oxide.
Alkaline Electrolysis
In the process of alkaline water electrolysis, a pair of electrodes is immersed in water containing alkaline electrolytes. Typically employed for large-scale, continuous production, alkaline electrolysis represents the most mature electrolysis technology with lowest long-term capital expenditure (CAPEX) given its low cost materials, readily available components, and the simplicity of its design. Nonetheless, it exhibits limited compatibility with intermittent production, which makes it less suitable for production using renewable energy sources.
Proton Exchange Membrane (PEM) Electrolysis
Proton exchange membrane (PEM) electrolyzers utilize a solid polymer electrolyte instead of a liquid alkaline water solution. The majority of renewable hydrogen projects in development today use PEM electrolysis. The main advantage PEM technology holds over alkaline technology is its suitability for intermittent production and consequent compatibility with intermittent renewable energy sources like wind and solar. Commercially viable but less mature than alkaline water electrolyzer technology, the current state of PEM technology can be likened to the state of battery energy storage technology around eight or ten years ago — while the technology is well-established, increased demand is necessary to push prices down.
To provide an overview of a general PEM electrolyzer system, the accompanying schematic diagram outlines the different system components, including the stack, the mechanical balance of plant, and the electrical balance of plant.
Within the electrical generation industry, the term “stack” refers to the equipment directly responsible for power production. Within a renewable hydrogen plant, the stack is the PEM electrolyzer unit and is often called the electrolyzer stack. Three main components make up a PEM electrolyzer stack: a membrane-electrode assembly (MEA), a current collector, and bipolar plates. The MEA consists of a membrane, typically composed of a composite copolymer, coated with a catalyst on each side, thereby separating the cathode from the anode. At the anode, water reacts to form hydrogen ions with a positive charge (protons) and oxygen. The hydrogen ions then selectively move across the PEM to the cathode. The current collector facilitates the flow of electrical current and product gasses out of the stack, while the bipolar plates, acting as electrodes, facilitate the circulation of water and gasses.
“Balance of Plant” (BoP) is a term that describes the equipment within a power plant other than the generator and, in this specific instance, refers to the equipment not directly involved in creating hydrogen. Mechanical BoP comprises water supply, plumbing, piping, heat exchangers, condensers, and related elements while electrical BoP encompasses any electrical equipment required to power the stack. In the diagram above, the PEM electrolyzer system is powered by AC power connected to the grid.
Solid Oxide Electrolysis
Solid Oxide Electrolyzer Cells (SOEC) are solid oxide fuel cells run in reverse, rendering them regenerative fuel cells. Like PEMs, SOECs use a solid oxide material as an electrolyte to convert electrical energy into chemical energy, splitting water into hydrogen and oxygen. However, the solid oxide material used by SOECs, typically zirconium dioxide, is a ceramic. SOECs have the potential to offer lower material costs and higher efficiency than PEM electrolyzers. Additionally, their reversibility enables electricity generation from stored hydrogen without needing a separate fuel cell or gas turbine power plant. It should be noted that SOECs are still in the developmental phase.
Manufacturers of PEM Electrolyzers
Several prominent manufacturers including Cummins, ITM Power, Nel Hydrogen, Siemens, and Plug Power, have developed electrolyzers in the 1 MW range or greater. The PEM electrolyzer industry is experiencing significant growth. Existing manufacturers are rapidly expanding capacity, and new market entrants are joining the industry. Undergoing a wave of consolidation, the industry of PEM electrolyzer manufacturing is witnessing rapid evolution and transformation. Some major acquisitions of the last four years include Cummins’ acquisition of the Canadian PEM manufacturer Hydrogenics, GTT’s acquisition of France’s Areva H2Gen, and Plug Power’s acquisition of Giner ELX.
In addition to further acquisitions as larger companies enter the field, we anticipate multinational conglomerates will expand their new energy technology portfolios and offer PEM electrolyzers, as Siemens AG has done.