Raul A. Marquez

Energy conversion technologies that are key to decarbonization efforts face significant durability challenges due to variable operation. Understanding the impact of variable operation on catalytic stability and identifying the key variables that dictate degradation is crucial for developing robust technologies. Here, we present a comprehensive investigation of the effects of variable operation on liquid alkaline water electrolysis. Our findings reveal that variable operation induces severe degradation of Ni, Fe, and Co catalytic films that is not observed during steady-state operation. By systematically interrogating the electrode discharge during simulated shutdown tests using Raman spectroscopy and mass spectrometry techniques, we uncover significant alterations caused by reverse currents in real time. These include changes in crystal structure, composition, film thickness, electronic conductivity, and dissolution rates. Lab-scale electrolyzer experiments further highlight the impact of variable operation on catalyst materials under relevant conditions. Finally, we provide guidelines for leveraging these insights to advance electrocatalysis research. This work underscores the importance of integrating realistic stressors into stability testing and offers practical guidelines for catalyst design, performance evaluation, and industrial implementation. Collectively, insights from this study will drive the development of more resilient energy conversion technologies.

Here, we introduce in-line continuous flow Raman spectroscopy (CFRS) as a spectroelectrochemical platform for quantifying interfacial pH swings generated during water-splitting. By monitoring phosphate ion speciation and controlling the hydrodynamics with a flow cell, we measure pH swings as a function of current density, flow rate, and distance from the electrode. Comparison with theoretical models reveals the impact of bulk pH, boundary layer thickness, and bubble dynamics at high current densities. Collectively, these findings establish CFRS as a platform for quantitatively investigating pH dynamics, offering critical insights for advancing electrochemical energy conversion technologies.

Understanding how electrode materials evolve in energy conversion and storage devices is critical to optimizing their performance. We report a comprehensive investigation into the impact of in situ metal incorporation on nickel oxyhydroxide oxygen evolution reaction (OER) electrocatalysts, encompassing four multivalent cations: Fe, Co, Mn, and Cu. We found that adding trace amounts of these cations to alkaline electrolytes alters the electrocatalytic and energy storage properties of NiOxHy films after electrochemical conditioning. As opposed to the well-known increase in OER activity induced by Fe, in situ incorporation of trace Co and Mn cations increases the total capacitance, while Cu incorporation does not proceed. We show that increasing Fe and Co concentrations leads to a maximum electrochemical performance attributed to a saturation threshold in the metal uptake. Depth profiling measurements reveal that metal incorporation is confined to the surface of the film, resulting in an interstratified structure that partially retains the more active, disordered phase at the surface. Building upon solid-state chemistry principles, we provide an in-depth discussion of four critical factors determining the occurrence of in situ metal incorporation, underscoring its nature as a cation exchange process. To further support this concept, we manipulate cation exchange by shifting the solubility equilibrium and via ion complexation. By providing a better understanding of in situ metal incorporation, our results underscore its potential as a strategy for manipulating the surface chemical composition, thus advancing the development of electrochemical energy materials.

This work, inspired by similar advances in CO2 electrolysis, represents the next step in AWE electrocatalysis research. As illustrated in Figure 1, lab-scale electrochemical flow cells harmonize stability evaluation and mark an advancement toward meeting industrial requirements. This initial effort aims to establish a straightforward protocol and comparison platform for evaluating and validating electrocatalysts in AWE. We hope this guide facilitates the transition to more realistic testing and promotes rigorous examination of electrocatalytic stability.

Transition metal borides, carbides, pnictides, and chalcogenides (X-ides) have emerged as a class of materials for the oxygen evolution reaction (OER). Because of their high earth abundance, electrical conductivity, and OER performance, these electrocatalysts have the potential to enable the practical application of green energy conversion and storage. Under OER potentials, X-ide electrocatalysts demonstrate various degrees of oxidation resistance due to their differences in chemical composition, crystal structure, and morphology. Depending on their resistance to oxidation, these catalysts will fall into one of three post-OER electrocatalyst categories: fully oxidized oxide/(oxy)hydroxide material, partially oxidized core@shell structure, and unoxidized material. In the past ten years (from 2013 to 2022), over 890 peer-reviewed research papers have focused on X-ide OER electrocatalysts. Previous review papers have provided limited conclusions and have omitted the significance of “catalytically active sites/species/phases” in X-ide OER electrocatalysts. In this review, a comprehensive summary of (i) experimental parameters (e.g., substrates, electrocatalyst loading amounts, geometric overpotentials, Tafel slopes, etc.) and (ii) electrochemical stability tests and post-analyses in X-ide OER electrocatalyst publications from 2013 to 2022 is provided. Both mono and polyanion X-ides are discussed and classified with respect to their material transformation during the OER. Special analytical techniques employed to study X-ide reconstruction are also evaluated. Additionally, future challenges and questions yet to be answered are provided in each section. This review aims to provide researchers with a toolkit to approach X-ide OER electrocatalyst research and to showcase necessary avenues for future investigation.

In this Viewpoint, we describe six practices to prepare, characterize, and validate the quality of alkaline electrolytes used in electrochemical energy systems. By adapting previous procedures and performing specific measurements, we provide a unified protocol to prepare and purify alkaline electrolytes, standardize their concentrations, determine their elemental compositions, provide statistical metrics, and examine their electrochemical properties.

Alkaline water electrolysis, a promising technology for clean energy storage, is constrained by extrinsic factors in addition to intrinsic electrocatalytic activity. To begin to compare between catalytic materials for electrolysis applications, these extrinsic factors must first be understood and controlled. Here, we modify extrinsic electrode properties and study the effects of bubble release to examine how the electrode and surface design impact the performance of water electrolysis. We fabricate robust and cost-effective electrodes through a sequential three-dimensional (3D) printing and metal deposition procedure. Through a systematic assessment of the deposition procedure, we confirm the close relationship between extrinsic electrode properties (i.e., wettability, surface roughness, and electrochemically active surface area) and electrochemical performance. Modifying the electrode geometry, size, and electrolyte flow rate results in an overpotential decrease and different bubble diameters and lifetimes for the hydrogen (HER) and oxygen evolution reactions (OER). Hence, we demonstrate the essential role of the electrode architecture and forced electrolyte convection on bubble release. Additionally, we confirm the suitability of ordered, Ni-coated 3D porous structures by evaluating the HER/OER performance, bubble dissipation, and long-term stability. Finally, we utilize the 3D porous electrode as a support for studying a benchmark NiFe electrocatalyst, confirming the robustness and effectiveness of 3D-printed electrodes for testing electrocatalytic materials while extrinsic properties are precisely controlled. Overall, we demonstrate that tailoring electrode architectures and surface properties result in precise tuning of extrinsic electrode properties, providing more reproducible and comparable conditions for testing the efficiency of electrode materials for water electrolysis.

Flow devices fabricated by means of 3D-printing offer an economic and effective approach for testing different electrochemical systems at the laboratory scale. Here, the fabrication and optimization of a novel filter-press electrochemical reactor is described. 3D-printing is used to obtain critical components of the device as a sustainable and efficient manufacturing approach. Hydrodynamics and mass transfer of different flow distributors, turbulence promoters, and nickel foam, as a three-dimensional (3D) electrode, were evaluated by a convenient set of well-known techniques for filter-press reactor characterization. Furthermore, the chemical stability of 3D-printed materials was assessed in several electrolytes used for common electrochemical applications. Designed configurations and geometries exhibited enhanced turbulence and large mass transfer coefficients, which make them adequate for processes such as electrosynthesis, electrodeposition, and electrochemical water splitting. Ultimately, superior performance was validated for nickel foam, demonstrating robustness of the reactor for realistic evaluation of electrocatalytic materials. Therefore, the proposed electrochemical reactor provides a low-cost and versatile alternative for testing electrochemical systems in a wide range of applications.

Research on electrochemical water splitting has experienced significant growth in interest in transition metal borides, carbides, pnictides, and chalcogenides, owing to their notable catalytic performance. These materials, collectively called X-ides, are often considered promising electrocatalysts for the oxygen evolution reaction (OER). However, under the strongly oxidizing conditions of the OER, transition metal X-ides often act as precatalysts, undergoing in situ reconstruction to a different, catalytically active phase. Discrepancies exist in the literature, with some studies claiming the absence of such transformations. Building upon previous efforts to elucidate catalytic performance trends in the community, this Perspective discusses a more nuanced approach to X-ide research, emphasizing the need to reassess our understanding of their chemical stability and the significance of the in situ reconstruction process. By discussing the role of experimental and computational databases, we present strategies for predicting X-ide stability and stress the importance of thorough experimental validation. Moreover, we highlight the use of machine learning to extract meaningful insights from these data and urge the community to adopt a standardized, systematic reporting of X-ide performance. Finally, we provide strategic guidelines and directions to advance transition metal X-ide research, ultimately enhancing their future application for a sustainable hydrogen economy.

Electrochemical energy conversion and storage devices are pivotal in transforming our society and advancing sustainability. Therefore, educating students in electrochemistry, the fundamental backbone of these technologies, is essential for preparing a new generation of professionals and raising public awareness of the role of these technologies in mitigating environmental challenges. However, a critical challenge lies in teaching electrochemistry through captivating and interactive approaches, particularly for younger learners. Herein, we outline a week-long workshop designed to immerse high school and undergraduate students in the world of electrochemical energy conversion and storage. The workshop was meticulously crafted to ensure a comprehensive exploration of electrochemistry fundamentals, operational principles of energy devices, real-world applications, and their societal impacts. Through mini-lectures, demonstrations, class discussions, educational games, and collaborative projects based on active learning, this workshop aims to improve the students’ understanding of electrochemistry and promote an appreciation for its critical role in society. Course evaluations indicate that our approach cultivates a stimulating learning environment. This initiative serves as a model for future educational programs in electrochemistry, aiming to equip students with the knowledge and inspiration needed to contribute to a sustainable future.