Alkaline Exchange Research Articles

Oxygen Plasma Triggered Co-O-Fe Motif in Prussian Blue Analogue for Efficient and Robust Alkaline Water Oxidation.

In the context of oxygen evolution reaction (OER), the construction of high-valent transition metal sites to trigger the lattice oxygen oxidation mechanism is considered crucial for overcoming the performance limitations of traditional adsorbate evolution mechanism. However, the dynamic evolution of lattice oxygen during the reaction poses significant challenges for the stability of high-valent metal sites, particularly in high-current-density water-splitting systems. Here, we have successfully constructed Co-O-Fe catalytic active motifs in cobalt-iron Prussian blue analogs (CoFe-PBA) through oxygen plasma bombardment, effectively activating lattice oxygen reactivity while sustaining robust stability. Our spectroscopic and theoretical studies reveal that the Co-O-Fe bridged motifs enable a unique double-exchange interaction between Co and Fe atoms, promoting the formation of high-valent Co species as OER active centers while maintaining Fe in a low-valent state, preventing its dissolution. The resultant catalyst (CoFe-PBA-30) requires an overpotential of only 276 mV to achieve 1000 mA cm-2. Furthermore, the assembled alkaline exchange membrane electrolyzer using CoFe-PBA-30 as anode material achieves a high current density of 1 A cm-2 at 1.76 V and continuously operates for 250 hours with negligible degradation. This work provides significant insights for activating lattice oxygen redox without compromising structure stability in practical water electrolyzers.

Oxygen Plasma Triggered Co‐O‐Fe Motif in Prussian Blue Analogue for Efficient and Robust Alkaline Water Oxidation

In the context of oxygen evolution reaction (OER), the construction of high‐valent transition metal sites to trigger the lattice oxygen oxidation mechanism is considered crucial for overcoming the performance limitations of traditional adsorbate evolution mechanism. However, the dynamic evolution of lattice oxygen during the reaction poses significant challenges for the stability of high‐valent metal sites, particularly in high‐current‐density water‐splitting systems. Here, we have successfully constructed Co‐O‐Fe catalytic active motifs in cobalt‐iron Prussian blue analogs (CoFe‐PBA) through oxygen plasma bombardment, effectively activating lattice oxygen reactivity while sustaining robust stability. Our spectroscopic and theoretical studies reveal that the Co‐O‐Fe bridged motifs enable a unique double‐exchange interaction between Co and Fe atoms, promoting the formation of high‐valent Co species as OER active centers while maintaining Fe in a low‐valent state, preventing its dissolution. The resultant catalyst (CoFe‐PBA‐30) requires an overpotential of only 276 mV to achieve 1000 mA cm‐2. Furthermore, the assembled alkaline exchange membrane electrolyzer using CoFe‐PBA‐30 as anode material achieves a high current density of 1 A cm‐2 at 1.76 V and continuously operates for 250 hours with negligible degradation. This work provides significant insights for activating lattice oxygen redox without compromising structure stability in practical water electrolyzers.

Review of AEM Electrolysis Research from the Perspective of Developing a Reliable Model

This review thoroughly examines recent progress, challenges, and future prospects in the field of alkaline exchange membrane (AEM) electrolysis. This emerging technology holds promise for eco-friendly hydrogen production. It blends the benefits of traditional alkaline and proton-exchange membrane technologies, enhancing affordability and operational efficiencies by utilizing non-precious metal catalysts and operating at reduced temperatures. This study discusses key developments in materials, electrode design, and performance enhancement techniques. It also highlights the strategic role of AEM electrolysis in meeting global energy transition targets, like achieving Net Zero Emissions by 2050. An in-depth exploration of the operational fundamentals of AEM water electrolysis is provided, noting the technology’s early stage development and the ongoing need for research in membrane-electrode assembly assessment, catalyst efficiency, and electrochemical ammonia production. Moreover, this review compiles results on different cell components, electrolyte types, and experimental approaches, providing insights into operational parameters critical to optimizing AEM performance. The conclusion emphasizes the necessity for continuous research and commercialization efforts to exploit AEM electrolysis’s full potential across diverse industries.

Development of an efficient bifunctional electrocatalyst based on Co/CoSe2 nanoparticles embedded in N, Se co-doped carbon for AEMFC and rechargeable Zn-air battery

We suggest a hollow-structured N, Se dual-doped carbon framework embedded with Co/CoSe2 nanoparticles (Co/CoSe2@NSeC) as highly efficient bifunctional electrocatalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The prepared electrocatalyst exhibits high electrochemical active surface area attributed to its unique hollow/porous structure and defective heteroatom doping sites. Furthermore, the strongly coupled heterojunction between Co and CoSe2 species not only provides abundant and highly active sites but also generates built-in electric field, thereby promoting electron transfer during the electrocatalytic reaction. Based on the above considerations, the prepared catalyst shows excellent bifunctional electrocatalytic performance. Leveraging the excellent ORR activity of Co/CoSe2@NSeC, alkaline exchange membrane fuel cells (AEMFC) with the Co/CoSe2@NSeC as air cathode exhibits high power density of 171.23 mW cm2. Furthermore, the rechargeable Zn-air battery employing the Co/CoSe2@NSeC shows high specific capacity (729.4 mAh gZn−1), peak power density (192.88 mW cm2), and sustained stability over 300 cycles.

Enhancement of Catalytic Activity via Inevitable Reconstruction of the Ni-Mo Interface for Alkaline Hydrogen Oxidation.

The inevitable oxidation of nickel-metal-based catalysts exposed to the air will lead to instability and poor reproducibility of a catalytic interface, which is usually ignored and greatly hinders their application for the catalysis of alkaline hydrogen oxidation. The details on the formation of a world-class nickel-based HOR catalyst Ni3-MoOx/C-500 are reported via an interfacial reconstruction triggered by passive oxidation upon air exposure. Interfacial reconstruction, initiated with various Ni-Mo metal ratios and annealing temperature, can fine-tune the Ni-Mo interface with an increased work function and a reduced d-band center. The optimized Ni3-MoOx/C exhibits a record high mass activity of 102.8mA mgNi -1, a top-level exchange current density of 76.5µA cmNi -2, and exceptional resistance to CO poisoning at 1000ppm CO for hours. The catalyzed alkaline exchange membrane fuel cell exhibits a maximum power output of 600mW cm-2 and excellent stability, ranking it as one of the most active non-precious metals HOR catalysts to date.

Microstructural Tuning of High‐Performance Bacterial Cellulose Anion Exchange Membranes via Constrained In Situ Polymerization and Double Chemical Cross‐Linking

AbstractHigh electrochemical and durability anion exchange membranes (AEMs) are a vital material for Flexible zinc‐air batteries (F‐ZAB) and AEM water electrolysis (AEMWE) to achieve green economy and environmental protection. However, the existing AEMs possess the disadvantages of a complicated preparation process, poor homogeneity, and unsatisfactory electrochemical performance. Here, a novel alkaline exchange membrane is synthesized using bacterial cellulose (BC) as the matrix, incorporating constrained in situ Poly (diallyldimethylammonium chloride) (PDDA) polymerization and double chemical cross‐linking techniques. By adjusting the microstructure, a unique long‐range order and dense internal structure to address the issue of loose bonding between PDDA and BC is established and achieve the purpose of rapid OH− conduction. The membranes exhibit excellent application properties, with excellent ionic conductivity (145.12 mS cm−1) and superb mechanical strength (73.26 MPa). Consequently, the membrane is assembled into the F‐ZAB, and the unprecedented power density of 258.7 mW cm−2 can be achieved at room temperature. Moreover, the membrane also can reach 3.0 A cm−2 at 2.3 V, indicating good prospects in the field of water electrolysis in 6 m KOH. The approach paves a new path for manufacturing AEMs for green energy and environmental applications.

Exploring the Role of Coordinating Environments on Durability of Nickel-Based Catalysts for Hydrogen Evolution Reactions

Ni-based platinum-group-metal (PGM)-free catalysts for hydrogen evolution reaction have been considered viable for the commercialization of alkaline exchange membrane water electrolysis (AEMWE) due to their high activity and low cost. Even though several highly active Ni-based catalysts have been developed in recent years, their long-term stability under commercially relevant conditions was not systematically assessed, preventing a direct comparison with the currently used catalysts. While not as active, the current commercial PGM-free catalysts are highly stable, with an operational life measured in decades. However, conducting durability assessments through long-term durability studies can take over 10,000 hours which is impractical. Consequently, accelerated stress tests (ASTs) specifically targeting the catalyst and simulating uncontrolled shutdown and high overpotential scenarios are needed to further improve AEMWE technology.In this presentation, the ASTs of several Ni-based catalysts with different coordination environments (nickel molybdenum, nickel cupferron1, Ni-NiO, and a novel high surface area de-alloyed Ni catalyst) will be explored. The catalysts were subjected to high overpotentials and uncontrolled shutdown cycles in both liquid electrolyte and AEMWE cells. The structure of these catalysts was observed using in situ Raman spectroscopy, XRD, TEM, and BET gas adsorption analysis and correlated to changes in electrochemical performance. The determination of the catalyst structure during these ASTs is paramount in designing durable PGM-free catalysts for improved AEMWE performance.1) Doan, H.; Kendrick, I.; Blanchard, R.; Jia, Q.; Knecht, E.; Freeman, A.; Jankins, T.; Bates, M. K.; Mukerjee, S. Functionalized Embedded Monometallic Nickel Catalysts for Enhanced Hydrogen Evolution: Performance and Stability. J. Electrochem. Soc. 2021, 168 (8), 084501. https://doi.org/10.1149/1945-7111/ac11a1.

Cyclic Olefin Copolymer-Based Reinforced Anion Exchange Membrane for Fuel Cell

Alkaline exchange membrane (AEM)-based fuel cells have emerged as a promising technology for clean energy conversion. In contrast to acidic proton exchange membrane in fuel cells, AEM fuel cells utilize an alkaline membrane AEM to facilitate the migration of hydroxide ions, offering advantages of economic earth-abundant catalysts and enhanced electrochemical reaction kinetics. However, AEMs that possess all characters of high ion conductivity, good chemical stability under high pH and temperature, robust mechanical properties, scalable synthesis, and low manufacturing costs are rare until now.Herein, we present quaternary ammonium-functionalized cyclic olefin copolymers (COCs) as a new class of alkaline stable and low-cost AEMs. Furthermore, we developed reinforced composite AEM by impregnating the quaternary ammonium-functionalized COC into a mechanically robust matrix. The prepared COC-reinforced membrane exhibits outstanding hydroxide conductivity of 127 mS/cm at 80°C and low swelling ratio in liquid water, and excellent mechanical properties with a tensile strength > 50 MPa, and elongation at break > 248%. The H2-O2 fuel cell test exhibited a maximum peak power density of >1.2 W cm-2 at 80°C with a low high-frequency resistance (HFR) under 0.1 Ohm cm2.

Rapid Joule-heating fabrication of Ce-doped Co/CoO on carbon nanotubes for efficiently electrocatalytic hydrogen production

In this work, Ce-doped Co/CoO grown on carbon nanotubes was prepared by a novel Joule-heating method. The rapid heating and cooling process caused lattice disorder, which effectively exposed active sites and further improved electrocatalytic activity in the hydrogen evolution reaction (HER). As prepared Ce-Co/CoO@CNTs by the rapid Joule-heating method exhibited excellent performance with an overpotential of only 47.6 mV @10 mA cm−2 in 1 M KOH electrolyte. Furthermore, as-prepared samples maintained exceptional chemical stability, with almost no decay observed even at high current densities (700 mA cm−2) for 200 h. In addition, using Ce-Co/CoO@CNTs catalyst in the alkaline exchange membrane (AEM) electrolyzers, an outstanding operating performance (1.62 V at 10 mA cm−2) was tested for overall water splitting. The formation of a large number of surface defects increased the number of active sites and accelerate the charge transfer. Additionally, the construction of Co/CoO heterojunctions modulated the electronic structure of the interfacial domains, optimizing reaction kinetics and providing a new pathway for designing and synthesizing efficient HER catalysts.

Oxygen reduction reaction platinum group metal-free electrocatalysts derived from spent coffee grounds

The annual generation of coffee waste has overtaken 6 million metric tons, becoming a serious environmental problem. Herein, we report the fabrication of bimetallic electrocatalysts synthesized by 1) pyrolyzing spent coffee grounds (SCGs) at 400, 600, 800 and 1000 °C, 2) activating the as-obtained char with KOH and 3) functionalizing the activated carbon with iron(II) and manganese(II) phthalocyanine. The final electrocatalysts showed a high degree of amorphousness, defectivity (increasing with temperature) and high specific surface area (up to 1820 m2 g−1). In half-cell compartment (0.1 M KOH electrolyte), the top-notch material in terms of oxygen reduction reaction (ORR) activity and selectivity was CFeMn_600, which showed the same half-wave potential (E1/2) compared to Pt/C standard along with a lower peroxide production. These outstanding results could be attributed to a high surface area, a Fe-Mn synergy, and an abundance of C-N defects. The performance of CFeMn_600 as a cathode material in alkaline exchange membrane fuel cells (AEMFC) showed an open circuit voltage (OCV) of 0.890 V and power density of 30 mW cm−2. Notwithstanding, this research is one of few cases where a waste-derived electrocatalyst is tested in a real AEMFC, thus becoming a pioneer in the fuel cell study of waste-derived electrode materials.

Interfacial engineering of high-performance Fe2P2O7-based electrocatalysts for alkaline exchange membrane fuel cells

Fuel cells promise high energy density and energy conversion efficiency but are plagued by the scarcity of platinum for facilitating the oxygen reduction reaction (ORR). Herein, a facile synthesis of a heterojunction electrocatalyst of ZIF-8 derived carbon (Z8C) supported Fe2P2O7 (Fe2P2O7@Z8C) is reported. The electrocatalyst exhibited higher half-wave potential than the state-of-the-art Pt/C catalyst by more than 33 mV and achieved a peak power density of 152.47 mW cm−2, outperforming the Pt/C-driven cell by ca. 14.5 mW cm−2 in alkaline membrane electrode assemblies under similar operating conditions. X-ray photoelectron and X-ray absorption spectroscopic studies suggested a spontaneous electron redistribution across the heterojunction interface in Fe2P2O7@Z8C. Density functional theory calculations indicated that the electron redistribution may remarkably promote the intrinsic activity of Fe2P2O7@Z8C toward the four-electron ORR pathway. These findings offer an indispensable strategy for rational design of highly efficient and durable non-noble electrocatalysts.

Optimizing Nickel Orbital Occupancy via Co‐Modulation of Core and Shell Structures to Accelerate Alkaline Hydrogen Electro‐Oxidation Reaction

AbstractNickel‐based catalysts are recognized as a promising alternative to platinum‐based catalysts for the alkaline hydrogen oxidation reaction (HOR) yet suffer from poor stability and relatively low activity. Herein, a nitrogen ligand‐assisted approach is reported to encapsulate nickel‐copper nanoparticles within few carbon layers, and by modulating the core and shell components/structure, the charge distribution in the nanostructures can be finely regulated. The optimized Ni93Cu7@NC catalyst exhibits outstanding HOR activity with an intrinsic activity of 61.0 µA cm−2 and excellent stability, which is among the most advanced Ni‐based HOR catalysts. Notably, an alkaline exchange membrane fuel cell utilizing this catalyst achieves a peak power density of 381 mW cm−2 and maintains stability at 100 mA cm−2 for over 24 h. Experimental and theoretical investigations unveil that the electron re‐distribution at the interface of NiCu core and nitrogen‐doped carbon reduces the electron occupancy in Ni 4s‐H 1s bonding orbitals and Ni 3dz2/yz‐O 2p antibonding orbitals, leading to a weakened hydrogen binding energy and enhance hydroxide binding energy. Consequently, the limiting energy for the HOR is reduced following a bifunctional mechanism on the Ni93Cu7@NC. This work provides a core‐shell co‐modulation strategy to accurately regulate the electronic structure of transition metals to design robust catalysts.

Single-metal-atom-anchored RuN2 monolayers: A high-performance electrocatalyst for alkaline hydrogen oxidation reactions

The development of alkaline exchange membrane fuel cells (AEMFCs) is severely hampered by the scarcity of efficient Pt-free catalysts for the anodic hydrogen oxidation reaction (HOR). In this work, we systematically explored the HOR performance of single 3d transition metal atom-doped RuN2 monolayers (TM-RuN2, TM = Ti-Zn) by density functional theory calculations. Formation energy, oxidation potential, and electronic structure analyses indicate that the Ti, V, Fe, Co, and Ni-doped RuN2 not only have a good conductivity, but also possess strong thermodynamic and electrochemical stability. For TM-RuN2, the ortho-N and metal (TM or ortho-Ru) atoms form a dual-active site for the adsorption of H* and OH*, respectively, where the adsorption strength is fine-tunable via the TM-modulated electronic structure. The HOR occurs preferentially through the H2 + OH*-H* + OH* mechanism on the pristine and Co, Ni, Cu, and Zn-doped RuN2, and the Tafel − H* + OH* mechanism on the Ti, V, Cr, Mn, and Fe-doped RuN2. The precisely balanced H* and OH* adsorption strength of Fe-RuN2 results in the ultra-low free energy barriers to HOR. Benefiting from the strong thermodynamic and electrochemical stability, good conductivity, and excellent HOR activity, Fe-RuN2 exhibits a huge potential as HOR electrocatalysts for AEMFCs.

Developing Alkaline Exchange Membranes Using Multisegmented Block Copolymers from Friedel–Crafts Hydroxyalkylation Polycondensation

Developing Alkaline Exchange Membranes Using Multisegmented Block Copolymers from Friedel–Crafts Hydroxyalkylation Polycondensation

Recent advances in metal-based electrocatalysts: from fundamentals and structural regulations to applications in anion-exchange membrane fuel cells

We present a comprehensive understanding of the alkaline hydrogen oxidation reaction (HOR), ammonium oxidation reaction (AOR), and oxygen reduction reaction (ORR) based on metal catalysts for H2 or NH3-fueled alkaline exchange membrane fuel cells.

Recent Advances in Platinum Group Metal Based Alloys for Alkaline Hydrogen Oxidation Reaction

AbstractThe development of efficient electrocatalysts for alkaline hydrogen oxidation reaction (HOR) is crucial to realize the commercialized application of alkaline exchange membrane fuel cells. Platinum group metals (PGMs) have been extensively used as alkaline HOR catalysts because they exhibit high activity and stability. Currently, searching for methods to improve the catalytic activity and reduce the loading of PGMs is the main research interest of PGM‐based electrocatalysts. The alloying method has been regarded as an effective strategy. In this review, we summarized various kinds of PGM‐based alloys, including traditional random alloys, single‐atom alloys, high‐entropy alloys and intermetallic compounds, and highlighted the challenges and future directions regarding the development of advanced PGM‐based alloys.

Anion Exchange Membrane Functionalized by Phenol-formaldehyde Resins: Functional Group, Morphology, and Absorption Analysis

We have developed a straightforward and uncomplicated technique for creating alkaline exchange membranes (AEMs) that possess both high alkaline durability and improved ionic conductivity. This method provides an appealing alternative to conventional approaches, notably by eliminating the need for the use of the carcinogenic reagent chloromethyl methyl ether, typically employed in AEM preparation. Examination of the membranes via scanning electron microscopy (SEM) reveals a consistently smooth surface. Augmenting the ion-exchange material's weight percentage in the casting solution results in enhanced water content, ion exchange capacity, and electrical conductivity. Importantly, our approach entirely circumvents the use of the hazardous chloromethy l methyl ether reagent, commonly associated with AEM preparation. TGA for thermal stability and chemical stability, conductivity with impedance data, and electrochemical tests are going on. The outcomes of this study present an appealing alternative to traditional methods for AEM synthesis.

(Keynote) Aerogel-Derived Nickel-Iron Oxide Catalysts for Oxygen Evolution Reaction in Alkaline Media

Low-temperature alkaline water electrolyzers, both liquid alkaline and—more recently—anion exchange membrane (AEM) ones, represent an attractive path towards large-scale generation of green hydrogen, possibly without relying on precious metals, otherwise required by the competing proton exchange membrane (PEM) electrolyzer technology. Of the two alkaline systems, the AEM electrolyzer offers an additional benefit of not needing highly concentrated alkaline solutions and, upon further development, possibly not requiring any electrolyte at all. The ultimate success of the AEM technology will depend though on progress in the development of several key materials: alkaline exchange membranes, electrode ionomers, and platinum group metal-free (PGM-free) electrocatalysts for the anode and the cathode. It will also depend on successful integration of the developed materials into a complete device, aiming especially at well-performing catalyst/membrane and catalyst/ionomer interfaces that are free of significant charge and mass transport losses.The focus of this work has been on NiFe oxide electrocatalysts for oxygen evolution reaction (OER) for alkaline media in low temperature electrolyzers. The catalysts have been derived from aerogels heat-treated at different temperatures. Depending on the synthesis temperature the catalysts have shown dissimilar OER activities and morphologies, required different activation procedures and incurred diverse structural changes during testing. In addition to extensive performance evaluation in a three-electrode electrochemical cell and a small electrolyzer, the catalysts have undergone wide-ranging physicochemical characterization with the purpose of identifying causes of the differences in their activity and performance durability. Characterization involved among others high-resolution scanning microscopic techniques and electron and X-ray spectroscopy methods (e.g., EELS, XPS, EXAFS/XANES).Of special interest in this research has been the development and optimization of catalyst activation approaches, both in-situ (in an operating cell) and ex-situ. The effect of ionomer type on catalyst performance and overall performance of NiFe catalysts in electrolyzer-type electrodes has been studied, too, and will be summarized in this presentation. Acknowledgement This work has been performed as part of catalyst development efforts in Electrocatalysis Consortium (ElectroCat), funded by U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE) via Hydrogen and Fuel Cell Technologies Office (HFTO).

Hydrogenation versus hydrogenolysis during alkaline electrochemical valorization of 5-hydroxymethylfurfural over oxide-derived Cu-bimetallics

The electrochemical conversion of 5-Hydroxymethylfurfural, especially its reduction, is an attractive green production pathway for carbonaceous e-chemicals. We demonstrate the reduction of 5-Hydroxymethylfurfural to 5-Methylfurfurylalcohol under strongly alkaline reaction environments over oxide-derived Cu bimetallic electrocatalysts. We investigate whether and how the surface catalysis of the MOx phases tune the catalytic selectivity of oxide-derived Cu with respect to the 2-electron hydrogenation to 2.5-Bishydroxymethylfuran and the (2 + 2)-electron hydrogenation/hydrogenolysis to 5-Methylfurfurylalcohol. We provide evidence for a kinetic competition between the evolution of H2 and the 2-electron hydrogenolysis of 2.5-Bishydroxymethylfuran to 5-Methylfurfurylalcohol and discuss its mechanistic implications. Finally, we demonstrate that the ability to conduct 5-Hydroxymethylfurfural reduction to 5-Methylfurfurylalcohol in alkaline conditions over oxide-derived Cu/MOx Cu foam electrodes enable an efficiently operating alkaline exchange membranes electrolyzer, in which the cathodic 5-Hydroxymethylfurfural valorization is coupled to either alkaline oxygen evolution anode or to oxidative 5-Hydroxymethylfurfural valorization.

One-pot synthesized Li, V co-doped Ni3S2 nanorod arrays as a bifunctional electrocatalyst for industrialization-facile hydrogen production via alkaline exchange membrane water electrolysis

The design of a bifunctional electrocatalyst with excellent performance in water electrolysis under high current densities for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with non-noble metals-based catalysts has been challenging. A novel bifunctional electrocatalyst constituted as the lithium and vanadium (Li, V) co-doped nickel sulfide (Ni3S2) nanorod arrays (LVN-0.1) is designed and investigated to take this challenge. The overall water splitting (OWS) electrolyzer constructed with our LVN-0.1 catalyst exhibited low cell voltages of 1.44 and 1.95 V to achieve 10 and 1000 mA/cm2, respectively, with excellent durability, which is almost the best Ni3S2-based electrocatalyst reported to date. The practical scale-up LVN-0.1 stack cell of 2 × 2 cm2 required 1.92 and 2.02 V to achieve high current densities at the industrial level at 500 and 1000 mA/cm2, respectively. Notably, our alkaline stack cell achieved a cell-efficiency of 61.9% and cell stability for 200 h at 1000 mA/cm2, while commercial alkaline cells have kept operating below 500 mA/cm2 to avoid the drop-off of binder-coated electrocatalysts. This study provides a facile way to design bifunctional electrocatalysts for realizing high efficient and stable hydrogen production by alkaline water splitting.