Conductivity Sensors for Hydrogen Fuel Cells

Hydrogen fuel cells are able to produce electricity with the chemical energy of hydrogen. This is a clean energy that only produces water, electricity, and heat as the main products and byproducts. Fuel cell technology is available in a wide range of applications, including transportation, warehouse logistics, global distribution, and backup power.

These cells use a polymer membrane and gas diffusion media for the electrolyte. In most cases, the fuel is hydrogen. These cells can run at low temperatures and make quick adjustments to meet changing power demands. The main advantage of using fuel cells instead of other combustion-based technologies is that they produce fewer emissions and offer better efficiency. Since they don’t have as many moving parts as other combustion technologies, they are quieter during operation.

Gas diffusion layers are used alongside direct menthol, phosphoric acid, and proton exchange membranes to maintain high thermal and electrical conductivity. The membrane is a porous sheet that can also control reactant gas flow. In recent years, fuel cell technology has been adopted by an increasing number of companies across different industries.

While these devices are able to convert the chemical energy from hydrogen into electricity, you must take steps to optimize fuel cell performance for the best results. There are four crucial aspects of fuel cell optimization, which include humidity control, temperature control, flow rates, and pressure control. This guide explores hydrogen fuel cells and the role that conductivity sensors play in optimizing them.

Understanding Conductivity Sensors

Conductivity is a type of measurement that’s designed to determine how well a solution conducts an electric current. This measurement can be obtained with a conductivity sensor, which is placed in an aqueous solution to identify its quality. Conductivity sensors can also be used to measure the water’s resistivity and TDS levels.

When a conductivity sensor is placed in a solution, current will flow if there are ions within the liquid. Otherwise, the solution won’t be conductive. For example, ultrapure water doesn’t emit a conductivity reading because there aren’t any ions within the liquid.

There are two types of conductivity sensors that can be used in hydrogen fuel cells, which include contacting and inductive sensors. Contacting sensors are most effective when used for ultrapure and pure applications. They provide high sensitivity and precision.

Inductive sensors are useful for a wider range of solutions and can be effective when conductivity readings are high. They don’t require much maintenance even when used in corrosive or dirty environments. Modern sensors can be placed in fuel cell applications to measure the thermal conductivity changes within the gas mixture.

Regardless of the type of conductivity sensor you choose, it will likely be comprised of two electrodes that can be placed in the solution at the same time. An electrical current is sent out and passed between the electrodes. The conductivity is based on the amount of current that’s in the solution. If the solution contains a considerable amount of dirt and other contaminants, you’ll likely receive a higher conductivity rating that indicates the water needs to be treated.

Most conductivity electrodes are made of gold or platinum. However, many types of conductivity materials can be used in electrodes. The specific type of material that’s used in your sensor can play a significant role in determining the precision of the measurement.

Before measuring conductivity, keep in mind that the two electrodes are known as the measuring electrode and the reference electrode. The measuring electrode is designed to identify the current when it flows through the solution. In comparison, the reference electrode provides a reference voltage that helps to deliver an accurate reading.

Most modern conductivity sensors are equipped with other features and technologies that can be useful when measuring the quality of water or hydrogen fuel cells. For example, these sensors can be outfitted with temperature sensor technology that allows for more precise conductivity readings. Since the solution’s temperature can impact the measurement, you’ll need to compensate for any changes that occur. An increase in temperature leads to a higher conductivity reading.

You can use conductivity sensors in numerous applications, which include monitoring the ongoing health of living cells and measuring the ion concentration in chemical solutions. You can also monitor hydrogen fuel cells and the coolant that’s used to cool the fuel cell stack.

Features to Look for in Conductivity Sensors

Not all conductivity sensors are suitable for hydrogen fuel cell applications. It’s highly recommended that you choose a sensor that offers modern features and capabilities. For example, some conductivity sensors provide four adjustable outputs, which include two analog and two digital ones.

You could also select a sensor that converts the main signal into different values and measuring units for more effective data. Some of the additional features that you should be on the lookout for include the following:

• A toroidal design that resists corrosion and fouling
• A resin body that offers a wide solvent tolerance
• Stability in temperatures as high as 175 degrees Fahrenheit
• A pressure rating of 150 psig
• Conductivity readings that reach as high as 2,000,000 uS
• Wide temperature compensation
• Long cable length for more measuring versatility
• A flange for a flow cell installation

Role of Conductivity Sensors in Fuel Cells

There are several types of fuel cells, which include solid oxide fuel cells and PEM fuel cells. To know how the conductivity of gas diffusion media is measured, you must understand the electrical resistivity of different components in PEM cells.

The electrical properties of these cells are mainly dependent on the material that the gas diffusion layers (GDLs) are made with. The porosity and geometry of the physical structure also play an important role in this process. To ensure the fuel cells maintain optimal performance, the GDLs need to be measured with a conductivity sensor.

You can also use this sensor to assess the effectiveness of the membrane material. Conductivity measurements help optimize fuel cell performance by informing manufacturers of the baseline readings that are needed to maintain optimal performance levels. Keep in mind that the fuel cell industry requires low conductivity levels that are at less than five microsiemens per centimeter.

Gas Diffusion Media in Hydrogen Fuel Cells

GDLs have several roles in a fuel cell application. It’s possible for a GDL to be coated with a catalyst, after which it’s known as a gas diffusion electrode (GDE). The GDL is a type of porous membrane that’s made with carbon fibers that are weaved into a cloth. It can also be made by pressing numerous carbon fibers together. Modern GDLs are often equipped with hydrophobic treatment and a microporous layer. These layers help ensure better contact with the membrane.

The GDL serves as the electrode that allows reactants to be diffused across a membrane that’s covered with a catalyst. Since the GDL has high porosity and a large surface area, the reactants will diffuse along the entire catalyst area of the membrane. This process ensures that electricity can be effectively transported from each catalyst site.

The GDL is also tasked with handling moisture control within the fuel cell. This task is accomplished by removing the water byproduct from the catalyst layer, which will prevent the chambers from being flooded. A small amount of water is kept on the surface of the catalyst layer to enhance the conductivity of the membrane material.

Measurement Techniques

There are several methods you can use to measure the effectiveness of gas diffusivity in fuel cells. It’s directly related to the performance of a fuel cell. One measurement involves identifying the through-plane effective diffusion coefficient. When performing this technique, the gas chamber within a carbon dioxide sensor is separated from the surrounding air by GDLs. Once the chamber is emptied with carbon dioxide, the decay of the GDL will be examined.

Conductivity sensors can be used to detect the change in the thermal conductivity of a gas mixture. These sensors are comprised of one die that’s contained in dry air and another that’s exposed to the surrounding gas mixture. This technique allows conductivity readings to be taken without needing to consider a poor signal-to-noise ratio. A significant change in conductivity readings may indicate that the fuel cell performance is weakening.

Need for Coolant Conductivity

Coolant conductivity is an important parameter when you’re attempting to maintain fuel cells. Hydrogen fuel cell stacks must be kept cool as they’re being used, which is why these systems contain coolant. Just like water, coolant conductivity can be measured with a basic sensor. Since fuel cells require precise electrical processes, you’ll likely need to monitor coolant conductivity.

While the coolant maintains the temperature in a fuel cell stack, it also helps to move heat away from important components within the system. If the quality of the coolant worsens, the thermal management process could become much more challenging. By regularly monitoring the conductivity of the coolant within the fuel cells, you can keep the readings within the target range.

Keep in mind that coolant conductivity is responsible for numerous electrochemical reactions that occur in the fuel cell stack. When the conductivity rises or falls outside of the ideal range, you may encounter higher energy losses, damage to the system, and poor heat transfer. If you’re unable to transfer heat away from important components, they can overheat, which could cause irreversible damage. Over time, these issues can lead to complete system failure.

Membrane Material Effectiveness

The semipermeable membrane within a fuel cell is impacted by operating conditions like flow rates, humidity, pressure, and temperature. These conditions must be effectively monitored and controlled to maintain optimal fuel cell performance.

While there are many different types of fuel cells, let’s take a look at the PEM variety. These cells operate best in a temperature range of 140-176 degrees Fahrenheit. To ensure efficient reactions in the cell, you must maintain this temperature range.

If the temperature dips too low or rises faster than intended, you may encounter issues like damage to fuel cell components, performance degradation, or decreased efficiency. It’s possible to manage the temperature with cooling plates, thermal management systems, and heat exchangers. Use the following techniques to maintain optimal performance:

• Humidity control: Use recirculating water or humidifiers to prevent membrane flooding or drying issues.
• Flow rates: Optimize flow rates by creating effective flow channels and implementing flow distributors.
• Pressure control: The performance of a fuel cell depends on the pressure from the reactant gases. You can achieve pressure control with pressure gradients, multiple stages, and high-quality compressors.

Conductivity sensors provide you with continuous readings and data that you can use to enhance the membrane material and make sure the fuel cell’s performance doesn’t falter. Conductivity readings for fuel cells should typically be low. If they start to climb, use the techniques mentioned above to bolster performance.

Benefits of Using Conductivity Sensors

There are many reasons why you should use conductivity sensors with hydrogen fuel cells, the primary of which is that you’ll be able to avoid performance losses. Conductivity sensors contribute to better fuel performance by allowing you to identify when the cell needs to be optimized.

If the conductivity readings are too low or too high, you might notice energy losses, poor heat transfer, and damage to internal components. These sensors give you quantifiable data that you can use to make the right decisions.

Optimized fuel cell operations can also save you a considerable sum of money. You’ll be able to avoid high energy consumption and damaged components. This technology is also clean, which can’t be said about other combustion technologies. By utilizing advanced measurement techniques in your facility, you should benefit from long-term cost savings.

Future Trends and Innovations

New technology is introduced to the water quality sensor market regularly. For example, modern conductivity sensors are capable of providing facilities with real-time data that allows for fast decisions. When a change occurs to the solution’s conductivity, you’ll be informed immediately. AI and machine learning may also be used to improve precision and accuracy.

As for hydrogen fuel cells, it’s believed that they will be adopted by many more industries in the coming years. While the auto and warehouse logistics industries are currently benefiting from this technology, adoption rates should continue to increase.

One recent advancement that might garner more interest from companies is the ability to make fuel cell components more durable, which can lead to better overall performance. Scientists are also attempting to increase power output, reduce manufacturing costs, and lengthen the lifespan of these cells. If these advancements can be made over the next few years, fuel cells should become more economically viable.

Evolving Hydrogen Fuel Cell Applications

Hydrogen fuel cells are used in many industries. For example, hydrogen bus programs have become increasingly popular over the past few years. Hydrogen power has proven to be highly effective when used for public transportation applications. Some countries in Europe are transitioning to electric buses that are hydrogen-powered. In the U.S., this technology has made its way to Philadelphia, Nevada, and California. We’ll likely see more hydrogen bus programs in the U.S. by the end of the decade.

This technology is also effective when applied to backup power generation. Stationary fuel cells are currently available in uninterruptible power supply systems. These systems are required in data centers and hospitals that can’t have interruptions to their power. Microsoft implemented a hydrogen backup generator in one of its data centers in 2020. This experiment was a resounding success. The servers within the data center were able to run for two days with just hydrogen. Since hydrogen is a form of clean energy, better adoption of it should result in fewer pollutants in the air.

As for personal vehicles, many auto manufacturers are already using hydrogen fuel cells in their electric vehicles. For example, this technology has appeared in models like the BMW iX5 and the Honda CR-V.

Just like buses and cars, hydrogen fuel cells have also been placed in trains throughout the UK, South Korea, Japan, and Germany. However, many of these situations are test cases. Even though the technology has made considerable progress, more testing must be done to ensure trains can run entirely on hydrogen.

In the aerospace industry, numerous experimental projects are underway to determine the viability of hydrogen fuel cells in aircraft. For example, the Helios and Pathfinder prototypes have been created specifically to test these cells.

These prototypes are long-range unmanned vehicles that use hydrogen fuel cells that are replenished by electricity from solar arrays. This technique could accommodate continuous flights. As for commercial flights, ZeroAvia, Airbus, and Beyond Air expect to have hydrogen models available by 2025.

In recent years, hydrogen fuel cells have also begun to show up in marine applications. For example, a boat named the Energy Observer used a combination of wind turbines and solar panels to create its own hydrogen for the onboard fuel cell system. This technology might also be highly beneficial when used with military stealth submarines. In comparison to nuclear power, hydrogen fuel cells accommodate low exhaust heat and silent cruising.

Mobile power generation is among the most important applications of hydrogen fuel cell technology. Some of the first hydrogen fuel cells that NASA created were designed to deliver electricity for shuttles and rockets. General Motors recently announced that it was going to use hydrogen fuel cells in mobile generators.

Unmanned aerial vehicles currently play a major role in the retail and military industries. For example, these vehicles can deliver packages in some areas around the country. While UAVs are powerful enough to fly for an extended period, battery-powered models are limited in regard to range and power.

These challenges can be bypassed with hydrogen fuel cells, which allow for a maximum range that’s three times better than that of battery-based systems. It’s also possible to refuel hydrogen cells in just a few minutes.

Conclusion

Conductivity sensors tell you when a solution is able to conduct electricity. In a water sample, high conductivity readings indicate that there are a lot of ions in the water, which means that it’s likely contaminated. If your facility manufactures hydrogen fuel cells, conductivity sensors can be invaluable in helping you maintain the performance of a hydrogen fuel cell and determine if the gas diffusion rates are high enough.