Leveraging demanding humidity measurement solutions to advance fuel cell test systems

A leading developer of high-quality instrumentation and software for electrochemical research and development, Scribner, LLC delivers solutions globally recognized as the gold standard for instrument control and data analysis. Specializing in manufacturing test equipment in the electrochemical energy conversion and storage space, Scribner demands that its fuel cell test systems produce a very stable, reproducible amount of water vapor, or humidity, within a gas stream. 

The challenge: Fuel cell test system calibration in high dew point environments

Water vapor plays a significant role in various electrochemical processes and reactions. Fuel cells, for example, convert the chemical energy of reactants — typically hydrogen and oxygen — into electrical energy. The fuel cell is comprised of two electrodes — anode and cathode — separated by an electrically insulating but ionically conducting ionomer film or membrane. The most common separator used in low-temperature fuel cells is the polymer electrolyte membrane (PEM), also called the proton exchange membrane. The fuel cell anode is fed hydrogen gas, where it is oxidized to form protons and electrons. The electrons are forced to travel through an external circuit, whereas the protons migrate through the PEM separator to arrive at the cathode. At the cathode, oxygen combines with the electrons and protons to form water. The electrical energy produced by the fuel cell does useful work, such as running an electric motor.

Proton conduction by the ionomer membrane strongly depends on the presence of water. PEMs are very poor conductors when dry, exhibiting high resistance and concomitant reduced fuel cell performance. In the presence of water, however, the membrane is a very good proton conductor, exhibiting low resistance, leading to improved fuel cell performance. In fuel cell testing, wherein humidity is an important test parameter, controlling the water vapor content of the hydrogen fuel and oxygen-containing air is very important. 

Companies developing high-quality fuel cell and membrane R&D instrumentation in high dew point environments face specific calibration and measurement challenges. Maintaining accurate and stable humidity levels is essential, as variation impacts the reproducibility and accuracy of fuel cell test data— with just one degree of dew point difference potentially resulting in relative humidity being off by 5%. Calibration procedures must account for the specific challenges of high-humidity environments and incorporate appropriate techniques to ensure reliable and consistent results.

Higher water vapor concentrations within electrochemical systems can also potentially result in excessive condensation, accumulation and damage to the system components, leading to measurement errors and reduced sensor lifespan.

In response to the demanding calibration requirements in high dew point environments, Scribner turned to Vaisala as the solution of choice for effective, state-of-the-art humidity and temperature monitoring. 

The solution: State-of-the-art humidity and temperature monitoring

Scribner’s fuel cell and membrane test systems need to produce a stable, reproducible dew point to precisely control humidification across a range of temperatures and pressures. Per a trusted customer’s recommendation, Scribner has leveraged Vaisala HMT337 Humidity and Temperature Transmitters since 2006 but has since moved to the HMP7 probe, Vaisala’s latest generation of the solution. 

“We were confident that if the Vaisala solution worked satisfactorily for them, it would also work for us,” said Dr. Kevin Cooper, principal scientist at Scribner. “We developed a custom dew point chamber that holds the Vaisala probe via a Swagelok fitting, is temperature-controlled and has porting for gas flow in and out. The chamber is heated to 10 degrees Celsius higher than the maximum expected dew point of the calibration procedure.”

Scribner uses Vaisala instruments internally to calibrate the humidifiers used in its fuel cell and membrane test systems. Designed to deliver gas with a dew point of up to 120 degrees Celsius, humidifiers are calibrated at a dew point of 80 degrees Celsius.

The OEM version of the HMT337, the HMT317, is used in the company’s 740 Membrane Test System (MTS) for real-time, in situ dew point monitoring. In conjunction with the measured process temperature, the measured dew point provides real-time relative humidity (RH), a critical process parameter for Scribner’s customers.

With state-of-the-art humidity and temperature monitoring integration, Scribner can achieve precise and accurate fuel cell test system calibration — even in demanding high-humidity environments.

The benefits: Accurate, repeatable and rapid measurement calibration where measurement performance is essential 

Incorporating reliable humidity sensors and monitoring systems is crucial for Scribner. Since regular calibration and validation of humidity control systems is essential to ensure accuracy and reproducibility, Scribner rotates four Vaisala instruments in and out of service in pairs, deploying the currently calibrated two for six months before sending them back to Vaisala for calibration.

“As a high-quality, reliable product, Vaisala HMT337 meets our required specifications with respect to operating temperature and dew point range, accuracy, etc. The instrument’s performance potential and ability to conduct high dew point measurements is critical — and the form factor works well for us,” continued Cooper. “We love the Vaisala instrument. Nothing but good things to say about it.” 

Running tests with controlled humidity conditions, monitoring the water vapor content and analyzing the consistency and repeatability of the results allows Scribner to optimize the design and operation of its humidification systems. Scribner has sold more than 700 integrated fuel cell test systems that include humidification systems and therefore require dew point calibration — and every humidifier unit was calibrated using a Vaisala instrument. Additionally, Scribner’s 740 MTS solution would not be viable without real-time, in situ dew point monitoring. The Vaisala HMT337 is critical to the function and performance of that instrument.

The HMT337, HMT317, HMM170 and the latest-generation HMP7 all utilize Vaisala’s unique warmed probe measurement technology that successfully addresses many high humidity measurement challenges. The warmed probe relies on a composite humidity and bonded temperature sensor. With a composite sensor, Scribner can monitor the dew point and, along with the test temperature, calculate the RH of the anode and cathode supplies.  

The warmed probe features a separate electrical resistance heater installed within the probe and controlled by the internally measured RH. The control algorithm design keeps the probe several degrees above ambient temperature to ensure water will not condense on the composite sensor even when the measurement environment is at the dew point temperature.

By utilizing high-quality humidity monitoring systems with appropriate sensitivity, accuracy and response time — like the Vaisala Relative Humidity and Temperature Probe HMP7 — Scribner ensures that its customers can confidently assess the performance, efficiency, stability and durability of fuel cells under various operating conditions. 

Precision measurement: Driving sustainability and innovation in the hydrogen economy

Hydrogen is set to be a significant part of the looming low-carbon economy due to its suitability for a wide range of applications. A leader in measurement instrumentation used in global hydrogen fuel cell market development, Vaisala is the only supplier to provide durable technology to support hydrogen fuel cell development since its early development phase in the mid-90s. Leading players, like Scribner, depend on Vaisala’s technology for the development of cost-effective, durable and high-quality fuel cell systems. 

Sustainability is a driving force in the fuel cell industry, shaping technological advancements, policy decisions and industry growth. Fuel cells offer a promising pathway to a more sustainable energy future by offering high energy efficiency, low emissions and rapid refueling, which enables a wide range of applications. With cost, performance and durability remaining critical challenges in the fuel cell industry, Vaisala’s industrial monitoring solutions empower forward-thinking organizations like Scribner to overcome critical technical barriers and develop cleaner and more versatile energy solutions.