水電解システムについて詳しく知るには

CRAIG GIFFORD:
Welcome to Ask Swagelok. I'm your host, Craig Gifford, here today with Hassan El Ghoul, who is a fluid systems engineer for Swagelok Ontario in Atlantic Canada. We've been talking, Hassan, about hydrogen production—specifically electrolyzers. In case someone is watching and a little bit new to the topic here, can you explain what an electrolyzer is?

HASSAN EL GHOUL:
Yeah, absolutely. An electrolyzer is a device that uses electrical current to split water into two types of molecules: oxygen and hydrogen (H₂). And this is what we're after. These molecules, at the operating conditions that we operate at, are in gaseous states. If we look at an electrolyzer, it has two compartments. Each compartment has an electrode: the cathode, which is negatively charged; and the anode, which is positively charged. Depending on the type of the electrolyzer, these two compartments are split using a different type of membrane. It could be a porous diaphragm or a polymer membrane depending on the type of the electrolyzer. There are so many types of electrolyzers out there. The most common ones are PEM (Proton Exchange Membrane Electrolyzers) and Alkaline Electrolyzers.

CRAIG GIFFORD:
So you mentioned there's multiple types of electrolyzers, specifically two main ones. Can you go into the differences between those two?

HASSAN EL GHOUL:
Yeah, absolutely. We'll start with the PEM, Proton Exchange Membrane Electrolyzer. This electrolyzer uses a polymer membrane, and that membrane allows the hydrogen ion, the proton, to pass from one electrode compartment to the other using electrical currents. So the hydrogen is generated at the cathode side. A few features about PEM: it takes high electrical current density, has a high output pressure—which is really good because it gives us high pressure, so no need for a lot of compression afterward. It uses noble metals in electrodes, like platinum, iridium, and gold. It has high electrochemical efficiency and high flexibility to load changes, meaning it's compatible with fluctuating sources like wind and solar.

CRAIG GIFFORD:
Oh great. Okay. Yeah. So, the other type of electrolyzer is alkaline.

HASSAN EL GHOUL:
Now, this uses a liquid electrolyte solution, like sodium hydroxide or potassium hydroxide, which we call lye. The hydroxide ion travels through a porous diaphragm. Some features about Alkaline Electrolyzer: compared to PEM, it takes low current density, producing lower efficiency, and generates low output pressures, meaning compression is required afterward. The electrodes are made of low-cost steel and plated with nickel alloys, making it much cheaper than PEM. However, it's not as flexible to load changes like PEM is.

CRAIG GIFFORD:
Okay. So, Hassan, as a new hydrogen production facility comes online, all of the fluid systems are subject to factory acceptance testing along the way. Even small leaks lead to inefficiencies and safety challenges. Can you walk us through some of those issues that arise with electrolyzers and the factors that can affect them?

HASSAN EL GHOUL:
When we think of electrolysis systems, and just like a lot of other hydrogen systems, we need to keep two big aspects in mind: safety—always comes first—and efficiency. Let's start with safety. Electrolyzers involve two critical gases: hydrogen (H₂), which is flammable and has a lower flammability limit of 4% in air, and oxygen, which obviously leads to combustion. That's the safety part. The second aspect is efficiency. In case of leakage, gases are lost to the atmosphere, wasting the energy put into electrolysis and compression. So the bottom line is we need adequate sealing technology designed specifically for small-molecule gases.

Plant size directly affects the electrolyzer in terms of capacity, efficiency, scalability, and economics. Addressing common issues involves looking at factors that drive efficiency: temperature (higher generally improves efficiency), electrode materials, current density, and electrolyte concentration, all of which influence hydrogen (H₂) production and electrolysis efficiency. Challenges include high capital costs, infrastructure requirements (compression, storage, refueling, virtual pipelines), efficiency compared to other hydrogen production modes like steam methane reforming, and competition in the market.

CRAIG GIFFORD:
So, Hassan, tell us, what else should designers be considering when building around electrolyzers?

HASSAN EL GHOUL:
Designers should consider subsystems surrounding the electrolyzer and overall fluid dynamics, including line sizing (avoiding excessive sizes that reduce efficiency), heat-recovery systems, valve sizing, conditioning subsystems for hydrogen before compression, relief valves, venting configurations, standards like CGA 5.5, purging, and hydrogen (H₂) quality. For sensitive applications like fuel cells, grab sampling or online analyzers can help ensure quality.

CRAIG GIFFORD:
Well, Hassan, thanks for sharing your knowledge about electrolyzers. We really appreciate it, and thank you for joining us at Ask Swagelok.