FUEL CELLS AND ELECTROLYZERS

Anion Exchange Membrane Electrolyzers

Anion exchange membrane water electrolyzers (AEMWEs) have emerged as a promising alternative for green hydrogen production, offering the potential to bridge the performance gap between proton exchange membrane (PEM) and alkaline water electrolyzers (AWE). Their alkaline environment enables the use of PGM-free catalysts and cost-effective cell components, while the high-performance zero-gap design improves efficiency and hydrogen production rates. While significant research has focused on advancing catalysts and membrane materials, these active components alone do not dictate overall electrolyzer performance. Electrode fabrication, cell assembly, and operating conditions play crucial roles in determining overall cell efficiency and voltage stability. Understanding these less-explored parameters is essential for improving real-world AEM electrolyzer operation.

One of our cores aims is to understand how aspects beyond catalysts and membranes, such as cell assembly parameters and operating conditions, impact AEM electrolyzer performance and longevity to better understand their contributions to overall efficiency and stability. This includes a systematic study of key cell assembly parameters, such as compression level, hardware materials, and design. In addition, we explore a wide range of operating conditions, including supporting electrolyte composition, electrolyte concentration, heating mode, operating temperature, flow configuration, and flow rates. Additionally, both in-situ and ex-situ diagnostic tests are conducted alongside degradation mechanism studies to gain deeper insights into the correlation between these factors and the cell behavior at the electrode level. Establishing clear relationships between these parameters and electrolyzer performance is essential for developing strategies that enhance efficiency and durability, ultimately advancing the commercial viability of AEM water electrolyzers.

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The result of our work to date has been high performing cells - with an operating voltage as low as 1.55 V at 1.0 A/cm2 - as well as long-life.  Lastly, our success with AEMFCs and AEMELs have afforded us the opportunity to investigate AEM-based unitized regenerative fuel cells (URFCs).  In this regard, we have worked to achieve very high round-trip efficiency (~50% @ 0.5 A/cm2) and we have the ability to operate reversibly while spending considerable time operating the cell in both directions (shown in the picture above).  

Seawater Electrolysis

The backbone underpinning the production of synthetic fuels is hydrogen.  Because of its ubiquity, water is expected to be the most effective hydrogen source, but increasing freshwater scarcity - initiated by climate change, population growth, and rising industrial and agricultural demands - could mean future competition between water for food and water for fuel.  Seawater electrolysis offers a sustainable solution, tapping into Earth's vast saline water reserves. However, there are several challenges.  First, direct seawater electrolysis suffers from issues like chloride corrosion, undesirable side reactions, and scale formation, all of which hinder performance and durability.  Second, "seawater" comes in a wide variety of forms and compositions – from oceans, seas, estuaries and bays across the world with seasonal variations in mineral concentrations.  Compositional variability adds complexity to the electrolyzer operation that can be difficult to overcome. 

Conventional systems require deionization before electrolysis, but we have created a new type of osmotic-driven electrolyzer that does not require water deionization before feeding it to the cell, reducing size, weight and energy demand while still having high operating current.  Through materials advancements and system optimizations, cells are routinely operating at high current density at ~1.8 V and one of our cells operated continuously for more than one year. By enhancing energy efficiency and ensuring long-term stability, our work advances cost-effective and scalable seawater electrolysis. Ultimately, this research supports large-scale, freshwater-independent hydrogen production, paving the way for a more sustainable energy future.

Anion Exchange Membrane Fuel Cells

Over the past decade, interest in Anion exchange membrane fuel cells (AEMFCs) has grown significantly.  The primary motivating factor for this attention is cost as it is widely accepted that alkaline pH conditions have the potential to drive down materials-level, stack-level and systems-level costs below the incumbent Proton Exchange Membrane Fuel Cell.  The intense effort around AEMFCs has led to the development of several very highly conducting, stable anion-exchange membranes (AEMs) and anionomers, high activity catalysts – still typically containing platinum group metals (PGMs).  But, for many years AEMFC performance remained very low.  

Our work in this area has been focused in several areas: the creation of Pt-free and PGM-free catalysts for both the oxygen reduction reaction and hydrogen evolution reaction, the control and design of the catalyst layer composition, structure and morphology, balancing the electrode/membrane/GDL water, and understanding carbonation processes and dynamics during AEMFC startup and operation.  One of our primary focuses as been water management at the anode during AEMFC operation.  During the oxidation of hydrogen at the anode, water is generated, and a lot of water arrives at the anode by electro-osmotic drag. If this water accumulates excessively, flooding can occur, cell performance and operational stability. To address this, our group has developed a number of water management strategies.  These have allowed our group to successfully increase the achievable energy density of AEMFCs from 0.5 W cm-2 to 3.5 W cm-2 as well as demonstrate 3600 hour durable performance. We have also integrated PGM-free catalysts into operating AEMFCs and have achieved Fe-N-C electrodes with a peak power density exceeding 2 W/cm2 and initial stability of 150 h.

Understanding and Mitigating the Effects of Fuel Cell Impurities

Fuel cells - both proton exchange membrane fuel cells (PEMFCs) and anion exchange membrane fuel cells (AEMFCs) - offer a clean and efficient alternative to conventional energy sources. However, their performance and longevity are highly dependent on the purity of both the fuel and the oxidant. Contaminants in either can lead to significant efficiency losses and may result in both recoverable and unrecoverable performance decline and component degradation.  At the hydrogen anode, gas phase contamination has been extensively studied, due to the use of reformate streams to power commercial cells; hence, the behavior of carbon monoxide, hydrogen sulfide, ammonia, etc. are well documented.  Cathode feed contamination, because of the more heterogeneous locations and sources, is less predicable and only a small fraction of the possible contaminants have been studied in the literature to date. 

The overall goal of our work is to understand how airborne contaminants impact cell performance. On of our most extensively studied systems has been CO2 fed to the AEMFC cathode, where the carbon dioxide reacts with hydroxide anions to produce carbonates that lead to three degradation mechanisms.  The first is the accumulation of carbonate anions at the anode - carbonates do not directly react with H2 at relevant potentials, which leads to a reduction in the anode pH, causing a Nerstian shift in the anode potential that reduces the cell voltage.  The second, also caused by carbonate accumulation, is lower hydroxide activity.  Lastly, the portion of charge carried by carbonate has lower mobility, reducing ionic conductivity.  On the PEMFC side, we are working with industrial partners to understand the effect of environment-specific impurities.   For example, ethylene is present in large quantities in produce processing facilities and petrochemical processing plants.  PEMFCs are quite sensitive to the presence of ethylene, experiencing sudden, though reversible voltage loss.  We have uncovered the underlying mechanisms for these and other processes and continue to develop solutions to mitigate them.