Alkaline Exchange Membrane Research Articles

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

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

Ruthenium-Manganese Solid Solution Oxide with Enhanced Performance for Acidic and Alkaline Oxygen Evolution Reaction.

Proton exchange membrane water electrolysers and alkaline exchange membrane water electrolysers for hydrogen production suffer from sluggish kinetics and the limited durability of the electrocatalyst toward oxygen evolution reaction (OER). Herein, a rutile Ru0.75 Mn0.25 O2-δ solid solution oxide featured with a hierarchical porous structure has been developed as an efficient OER electrocatalyst in both acidic and alkaline electrolyte. Specifically, compared with commercial RuO2 , the catalyst displays a superior reaction kinetics with small Tafel slope of 54.6 mV dec-1 in 0.5 M H2 SO4 , thus allowing a low overpotential of 237 and 327 mV to achieve the current density of 10 and 100 mA cm-2 , respectively, which is attributed to the enhanced electrochemically active surface area from the porous structure and the increased intrinsic activity owing to the regulated Ru>4+ proportion with Mn incorporation. Additionally, the sacrificial dissolution of Mn relieves the leaching of active Ru species, leading to the extended OER durability. Besides, the Ru0.75 Mn0.25 O2-δ catalyst also shows a highly improved OER performance in alkaline electrolyte, rendering it a versatile catalyst for water splitting.

Synergistic Ru/CeO2 heterostructure for alkaline hydrogen oxidation with high activity and CO tolerance

The lack of highly efficient and stable electrocatalysts for anodic hydrogen oxidation reaction (HOR) has limited the large-scale industrial application of alkaline exchange membrane fuel cell. In this work, a Pt-free Ru/CeO2 heterostructure electrocatalyst with outstanding catalytic activity and stability for alkaline HOR is developed. The synthesized Ru/CeO2 with synergistic heterogeneous interface exhibits a high kinetic current density reaching 21.7 mA cm−2 at an overportentail of 50 mV, which is nearly 11-fold higher than that of the contrastive Ru/C catalyst and almost the same as that of commercial Pt/C catalyst. Importantly, this electrocatalyst also shows high CO resistance that Pt/C catalyst lacks. Electrochemical results and spectral studies show that CeO2 efficiently adjust the electronic microenvironment of Ru site to promote Had adsorption, but also provide the adsorption sites for OHad at a low potential. As a result, the introduced CeO2 synergistically promotes hydrogen oxidation, H2O formation and CO removing, thereby enhancing the HOR performance of Ru nanoclusters.

Tuning surficial atomic configuration of Pt–Ir catalysts for efficient ammonia oxidation and low-temperature direct ammonia fuel cells

Low-temperature direct ammonia fuel cell via ammonia oxidation reaction (AOR) is one of the most attractive ways for ammonia utilization. The Pt–Ir alloyed catalysts have been proven greatly efficient in AOR to overcome the sluggish kinetics and complex multi-electron processes; however, it still remains challenging for further improvement because of the complexity of alloyed types and unclear fundamental understanding. Herein, we systematically fabricated a series of PtxIry/XC-72 catalysts via tuning the Pt/Ir compositions and these catalysts demonstrate significant composition-dependent behaviours in AOR, whereas the Pt favours increasing current densities and the Ir facilitates reducing onset potentials. Importantly, the actual surface Pt/Ir atomic configuration is totally different with the classic view for homogeneous alloys by combining catalytic and characteristic analyses. The Pt prefers to be segregated on the topmost surface. Then the quantified correlations between current density/onset potential and Pt composition in Pt − Ir nanoparticles (NPs) were further established and discussed. The onset potential of AOR is significantly reduced by Ir incorporation while it is insensitive to Ir contents. Accordingly, the well-studied Pt5Ir5/XC-72 catalyst was further employed in an alkaline exchange membrane fuel cell, exhibiting a peak power density (230.0 mW cm−2). Our work provides insights into the effect of Pt/Ir compositions on AOR, with the goal of catalysts engineering for AOR and ammonia fuel cells.

Clean H2 Production by Lignin-Assisted Electrolysis in a Polymer Electrolyte Membrane Flow Reactor.

Biomass-derived products, such as lignin, are interesting resources for energetic purposes. Lignin is a natural polymer that, when added to the anode of an alkaline exchange membrane water electrolyser, enhances H2 production rates and efficiencies due to the substitution of the oxygen evolution reaction. Higher efficiencies are reported when different catalytic materials are employed for constructing the lignin anolyte, demonstrating that lower catalytic loadings for the anode improves the H2 production when compared to higher loadings. Furthermore, when a potential of -1.8 V is applied, higher gains are obtained than when -2.3 V is applied. An increase of 200% of H2 flow rates with respect to water electrolysis is reported when commercial lignin is used coupled with Pt-Ru at 0.09 mg cm-2 and E = -1.8 V is applied at the cathode. This article provides deep information about the oxidation process, as well as an optimisation of the method of the lignin electro-oxidation in a flow-reactor as a pre-step for an industrial implementation.

Designing interface structures of nickel with transition metal nitrides for enhanced hydrogen electro-oxidation

Alkaline exchange membrane fuel cells are hampered by sluggish kinetics of the anodic hydrogen oxidation reaction (HOR). Recently, heterostructure catalysts show great potential in tailoring the electronic structure to promote catalytic performance. Herein, we systematically studied the alkaline HOR performance of heterostructures of nickel with transition metal nitrides (Ni/TMNs, TMN = δ3−MoN, δ1−MoN, and WN) by density functional theory calculations. The HOR on Ni/TMNs was found to proceed preferentially through the initial H2 dissociation into two adsorbed H*, followed by its recombination with the adsorbed OH* as the rate-determining step. The inter-regulated electronic structure at the interface can improve the degree of energy-level alignment between the d-band of interfacial Ni and the p-band of OH*, thus enhancing the adsorption free energy of OH* (ΔGOH*). Meanwhile, the downward shift of the p-band of interfacial N also weakens the adsorption free energy of H* (ΔGH*), making it more thermo-neutral. The precisely optimized H* and OH* adsorption at heterojunction interfaces substantially accelerates the recombination of H* and OH* in the HOR, resulting in the high HOR activity of Ni/TMNs. Among all considered catalysts, Ni/δ1−MoN shows the optimum HOR activity, resulting from the almost thermo-neutral ΔGH* and the strongest ΔGOH*.

Hydroxyl-Binding Energy-Induced Kinetic Gap Narrowing between Acidic and Alkaline Hydrogen Oxidation Reaction on Intermetallic Ru3 Sn7 Catalyst.

Developing highly efficient catalysts toward alkaline hydrogen oxidation reaction (HOR) and narrowing the kinetic gap between acidic and alkaline electrolytes are of great importance for the practical application of alkaline exchange membrane fuel cell . Herein, ordered Ru3 Sn7 /C intermetallic compound has been developed for the HOR under alkaline and acidic conditions. The authors demonstrate that the ordered intermetallic Ru3 Sn7 /C shows much enhanced HOR activity, stability, and CO-tolerance compared with its disordered RuSn solid solution alloy counterpart. More importantly, the authors find that the kinetic gap of HOR between acidic and alkaline media is significantly narrowed in the as-synthesized intermetallic Ru3 Sn7 /C catalysts. Combined experiment results and theoretical calculations, the authors understand that promoted hydroxyl-binding energy on Ru3 Sn7 /C derived from the intermetallic-induced strong electron interaction is responsible for the accelerated alkaline HOR performance and narrowed kinetic gap.

Fast and Durable Alkaline Hydrogen Oxidation Reaction at the Electron-Deficient Ruthenium-Ruthenium Oxide Interface.

The slow hydrogen oxidation reaction (HOR) kinetics under alkaline conditions remain a critical challenge for the practical application of alkaline exchange membrane fuel cells. Herein, Ru/RuO2 in-plane heterostructures are designed with abundant active Ru-RuO2 interface domains as efficient electrocatalysts for the HOR in alkaline media. The experimental and theoretical results demonstrate that interfacial Ru and RuO2 domains at Ru-RuO2 interfaces are the optimal H and OH adsorption sites, respectively, endowing the well-defined Ru(100)/RuO2 (200) interface as the preferential region for fast alkaline hydrogen electrocatalysis. More importantly, the metallic Ru domains become electron deficient due to the strong interaction with RuO2 domains and show substantially improved inoxidizability, which is vital to maintain durable HOR electrocatalytic activity. The optimal Ru/RuO2 heterostructured electrocatalyst exhibits impressive alkaline HOR activity with an exchange current density of 8.86mAcm-2 and decent durability. The exceptional electrocatalytic performance of Ru/RuO2 in-plane heterostructure can be attributed to the robust and multifunctional Ru-RuO2 interfaces endowed by the unique metal-metal oxide domains.

The Role of Discrepant Reactive Intermediates on Ru‐Ru2P Heterostructure for pH‐Universal Hydrogen Oxidation Reaction

AbstractDeveloping highly efficient electrocatalysts for hydrogen oxidation reaction (HOR) under alkaline media is essential for the commercialization of alkaline exchange membrane fuel cell (AEMFC). However, the kinetics of HOR in alkaline media is complicated, resulting in orders of magnitude slower than that in acid, even for the state‐of‐the‐art Pt/C. Here, we find that Ru‐Ru2P/C heterostructure shows HOR performance with a non‐monotonous variation in a whole pH region. Unexpectedly, an inflection point located at pH≈7 is observed, showing an anomalous behavior that HOR activity under alkaline media surpasses acidic media. Combining experimental results and theoretical calculations, we propose the roles of discrepant reactive intermediates for pH‐universal HOR, while H* and H2O* adsorption strengths are responsible for acidic HOR, and OH* adsorption strength is essential for alkaline HOR. This work not only sheds light on fundamentally understanding the mechanism of HOR but also provides new designing principles for pH‐targeted electrocatalysts.

The Role of Discrepant Reactive Intermediates on Ru-Ru2 P Heterostructure for pH-Universal Hydrogen Oxidation Reaction.

Developing highly efficient electrocatalysts for hydrogen oxidation reaction (HOR) under alkaline media is essential for the commercialization of alkaline exchange membrane fuel cell (AEMFC). However, the kinetics of HOR in alkaline media is complicated, resulting in orders of magnitude slower than that in acid, even for the state-of-the-art Pt/C. Here, we find that Ru-Ru2 P/C heterostructure shows HOR performance with a non-monotonous variation in a whole pH region. Unexpectedly, an inflection point located at pH≈7 is observed, showing an anomalous behavior that HOR activity under alkaline media surpasses acidic media. Combining experimental results and theoretical calculations, we propose the roles of discrepant reactive intermediates for pH-universal HOR, while H* and H2 O* adsorption strengths are responsible for acidic HOR, and OH* adsorption strength is essential for alkaline HOR. This work not only sheds light on fundamentally understanding the mechanism of HOR but also provides new designing principles for pH-targeted electrocatalysts.

Structural-enhanced bacterial cellulose based alkaline exchange membranes for highly selective CO2 electrochemical reduction and excellent conductive performance in flexible zinc-air batteries

In this work, OH - conducting membrane based on bacterial cellulose (BC) had been synthesized via modification with Poly(diallyldimethyl-ammonium chloride) (PDDA) and Poly(vinyl alcohol) (PVA) of different molecular weights using layer by layer method assisted by double cross-linking process. OH - conductivity and water uptake were intensively investigated by changing crosslinking conditions, KOH concentrations and different PVA molecular weights. Containing the maximum σ OH - reached up to 72.95 mS cm -1 at room temperature with water uptake being 877%, the LPVA-PDDA-BC-OH - membrane showed the lowest calculated activation energy value of 10.211 KJ mol -1 indicating that both Grotthus and vehicle mechanisms played an important role on ionic transportation. During the application of CO 2 electrochemical reduction (ERC) in 0.5 M KHCO 3 , the current density could reach up to 47.44 mA cm -2 at -1.06 V RHE while FE HCOO - achieved the maximum value of 67.89% which dampened only 7.09% after 20 h electrolysis. Furthermore, being assembled into the flexible zinc-air batteries (F-ZAB), the LPVA-PDDA-BC-OH - membrane exhibited excellent power density of 130.3 mW cm −2 at room temperature. • 1. Bacterial cellulose-based AEMs prepared by layer-by-layer/double-crosslinking method. • 2. OH - conductivity achieves 72.95 mS/cm at room temperature and 133.53 mS/cm at 80 o C. • 3. The current density of 51.34 mA/cm 2 at potential -1.36 V RHE can be achieved. • 4. The Faradaic efficiency of formate reaches up to 67.89% at -1.06 V RHE . • 5. OCV (1.42 V) and peak zinc-air battery power density (130.3 mW/cm 2 ) can be achieved. Through the combinations of layer-by-layer method and double cross-linking process, OH - conducting membrane based on bacterial cellulose (BC) had been synthesized with the modification by Poly (diallyldimethyl-ammonium chloride) (PDDA) and Poly (vinyl alcohol) (PVA) of different molecular weights. Under the help of PVA, an enhanced internal three-dimensional network could be easily constructed to overcome the disadvantage of excessively loosely binding in the BC membrane. Charge carrier PDDA were confirmed by FTIR and SEM to be firmly embedded into the network while studies on XRD and DSC indicated that amorphous content which was beneficial to ionic transfer and ions hopping held the large proportion in the membrane. Stability measurements such as thermogravimetric analysis, mechanical properties, alkaline and oxygen resistance were carried out, showing that the prepared membranes possessed excellent durable performance under various extreme conditions. Moreover, OH - conductivity and water uptake were intensively investigated by changing crosslinking conditions, KOH concentrations and PVA molecular weights. Achieving the maximum σ OH - of 72.95 mS cm -1 at room temperature, the LPVA-PDDA-BC-OH - membrane showed the lowest calculated activation energy value of 10.211 KJ mol -1 , indicating that both Grotthus and vehicle mechanisms played an important role on ionic transportation. When as-prepared LPVA-PDDA-BC-OH - membrane was applied for CO 2 electrochemical reduction (CO 2 ER) in 0.5 M KHCO 3 , current density could reach up to 47.44 mA cm -2 at -1.06 V RHE . Meanwhile, Faradaic efficiency for formate (FE HCOO - ) could achieve the maximum value of 67.89% that dampened only 7.09% after 20 h electrolysis. Furthermore, when as-prepared LPVA-PDDA-BC-OH - membrane was assembled into the flexible zinc-air batteries (F-ZAB), excellent power density of 130.3 mW cm −2 could be obtained at room temperature.

(Invited) Alkaline Membrane Electrolyzers: Catalysts, Degradation Mechanisms, and Materials Engineering for Performance and Durability

Commercialized membrane electrolyzers use acidic proton exchange membranes (PEMs). These systems offer high performance but require the use of expensive precious-metal catalysts such as IrO2 and Pt that are nominally stable under the locally acidic conditions of the ionomer. Alkaline-exchange-membrane (AEM) electrolyzers in principle offer the performance of commercialized PEM electrolyzers with the ability to use earth-abundant catalysts and inexpensive bipolar plate materials. I will present our fundamental work in understanding earth-abundant water-oxidation catalysts, including the use of integrated reference-electrode device architectures and cross-sectional materials analysis, as well as progress in building high-performance AEM electrolyzers. Baseline systems operate at 1 A·cm-2 in pure water feed at < 1.9 V at a moderate temperature of ~70 °C using either IrO2 or Co3O4 anode catalyst layers, PiperION alkaline ionomers, and stainless steel porous transport layers. These devices, however, degrade rapidly compared to PEM electrolyzers. The voltage profile corresponding to degradation has intial fast (~10 mV/h) and steady-state slow components (~1 mV/h), which we link to chemical and structural changes in the ionomer catalyst reactive zone. I will discuss these processes in electrolyzer devices and in model systems that are correlated with this performance loss, as well as present promising new strategies we have developed to mitigate degradation using novel ionomers and electrode catalyst compositions and architectures. Figure 1

(Invited) Progress and Perspective Towards Low-Cost High-Performance Anion Exchange Membrane Water Electrolysis

Hydrogen is at the forefront of clean energy use and storage in the goal to drastically reduce anthropogenic carbon dioxide and combat global climate change. However, hydrogen production to-date is accomplished via steam methane reforming which, for every ton of hydrogen produced 5.5 tons of CO2 is liberated. One viable technical solution for production of clean hydrogen is water electrolysis. To this end DOE has implemented the Hydrogen Earthshot initiative to cleanly produce hydrogen at 2 $/kg by 2025 and 1 $/kg by 2030.Of the several commercial water electrolysis technologies available, proton exchange membrane water electrolysis (PEMWE) currently offers the most benefits including operations at low temperature, differential pressure, and high current density (≥3 A/cm2). Commercialization of PEMWE has advanced rapidly despite several significant disadvantages which include the necessity of scarce expensive platinum-group metal (PGM) catalysts, expensive perfluorinated membranes, and significant environmental impacts of perfluorinated alkyl substances (PFAS) used in membrane production. The solution to these challenges is the development of alkaline exchange membrane water electrolysis (AEMWE) which retains the advantageous characteristics of PEMWE without the need for PGM catalysts or perfluorinated membranes.Here in, we report on our current progress of AEMWEs, which covers PGM-free catalyst development, low-cost and durable AEM development and electrode design development. From a commercial point of view, given a high-performance durable membrane, manufacturing MEAs is a critical next step toward commercialization. Therefore, development of an AEM with accessible thermal transitions prior to the onset of quaternary ammonium degradation is key to enabling proven MEA fabrication techniques such as hot-pressing and decal transfer of electrodes. Through a novel synthetic approach, we will describe the preparation of functionalized copolymers and terpolymers containing latent cross-linking functionality. Ultimately, we will demonstrate the manufacturability of MEAs from our PGM-free catalysts and membrane materials employing hot-pressing and decal transfer of electrodes along with single cell evaluations. We will also discuss factors that affect the degradation of AEMWEs and solutions to address these challenges.

Mechanistic Insight from Acetate Oxidation in Three-Electrode Cells and Flow Cells

Recent years has seen a tremendous growth in finding electrochemical pathways to produce chemicals and fuels because it is believed that pairing low-carbon electricity (solar, wind, nuclear) with renewable carbon sources and electrochemical processes will lead to a reduction in greenhouse gas emissions. One of the possible sources renewable carbon is biomass. During biomass upgrading, one of the byproducts is bio-oil, which contains a large amount of acetic acid. Acetic acid itself is a relatively low value product. Upgrading acetic acid (or its alkaline counterpart acetate) to a wider range of valuable products (e.g., methanol, ethylene) is extremely attractive. This can be done through thermochemical or electrochemical partial oxidation.Though acetic acid reactions have been studied for many years, details about its overall reaction mechanism still remain unknown. The most known and defended pathway in the literature is Kolbe electrolysis, where C-C bonds are formed from dimerization of methyl radicals as shown in Equation 1.2CH3COOH → 2CO2 + C2H6 + 2H+ + 2e- (Equation 1)However, aqueous environments have shown deviations from this dimerization. It is often overlooked that these reactions occur at high potentials and the state and role of the formed surface oxide are not well described in the literature. It is even not known what water-oxide mechanism dominates for the formation of alcohol-based products. Although prior work has shown that a three-electrode batch cell can produce the typical Kolbe products (ethane and carbon dioxide) at high faradaic efficiencies and steady state when the electrolyte bath is held at the pKa (4.7) and high voltage (>3.0V vs. RHE) – our previous studies have shown that the reaction environment (e.g. concentration, addition of supporting electrolyte, pH) can vary the effluent composition and reaction rate considerably. Also, our recent work has shown that transitioning the same catalyst to a lower-water environment in a flow cell can yield a completely different product profile than in aqueous media.Therefore, the purpose of this study is to demonstrate how the catalyst and reacting environment affect the formation of various C1 and C2 products from acetate electrochemical oxidation. To do this, custom-made two-electrode (similar to an alkaline exchange membrane electrolyzer) and three-electrode cells are used. Another variable that is manipulated is the voltage profile, where both constant voltage and pulsed experiments are performed. In the flow cell, several anode electrocatalysts (e.g., Pt, PtRu, NiO, IrOx) were dispersed in inks and sprayed onto porous transport layers. The anode feed was 0.5M potassium acetate. No gases were fed to the cathode, but hydrogen was collected from the exhaust. The anode effluent (gas and liquid mixture) was separated downstream in a simple vessel with UHP helium flowing through the incoming effluent to carry the gas for GC/MS analysis. Liquid samples were analyzed by ex situ and NMR with D2O solvent. Two-electrode and three-electrode results will be combined to provide new insights into acetate oxidation and pathways for future research and development will be discussed.

(Invited) Ir Strangelove: Or How I Learned to Stop Worrying and Embrace the PEM

There are extremely ambitious plans for rapid growth in hydrogen generation from renewables. PEM (polymer electrolyte membrane) electrolysis is particularly well suited to work with these intrinsically intermittent power sources due to their ability to duty cycle on the seconds timescale. An oft-sited liability of PEM is their reliance on precious group metal, PGM materials, specifically the use of Iridium for the oxygen evolution reaction (OER). Iridium is the rarest natural element on earth, with global production a scant 10 tons/year[1]. Speculation on increased demand has led to a recent price surge as well (Figure 1). Current Ir usage is estimated around 400 g Ir/MW of electrolysis[2]. This would put a cap of 25 GW/year of PEM electrolysis, assuming 100% of production was steered towards electrolysis, away from current uses, which include crucibles, chlor-alkali catalyst and spark plugs.These perceived challenges have motivated a healthy increase in alkaline exchange membrane (AEM) electrolysis, which can operate without the use of PGMs. AEMs have yet to demonstrate suitable durability, and have other system implications. The iridium availability cap can be greatly increased, however, by lowering Ir loadings on an areal basis and increasing current density. Furthermore, platinum which is far more prevalent can be used as a substitute, however at the cost of efficiency. This talk will look at how much iridium is needed, the likelihood of increased production, the cost iridium in PEM electrolysis, the use of substitutes, either membrane or catalyst systems to determine if the total addressable market for hydrogen electrolysis can be met by PEM. [1] M. Garside Statista, https://www.statista.com/statistics/585840/demand-for-iridium-worldwide/ [2] Ahmad Mayyas, Mark Ruth, Bryan Pivovar, Guido Bender, and Keith Wipke, Manufacturing Cost Analysis for Proton Exchange Membrane Water Electrolyzers . NREL, Aug, 2019. https://www.nrel.gov/docs/fy19osti/72740.pdf Figure 1