Session K64: Electrochemical Energy Conversion

Platinum Group and Transition Metal Alloy Electrocatalysts for Oxygen Evolution Reaction

Oxygen evolution reaction (OER) is important for green energy production and storage, and iridium oxide is the current benchmark for OER catalysts, but scarcity, high cost, and a negative environmental impact related to mining of precious metals limits their utility. Some progress has been made in identifying new metal and metal-oxide catalysts for this purpose, but industrial replacements remain out of reach. Studies of binary and some ternary alloys have shown increased catalyst performance with tuned selectivity and durability, yet the number of studies of alloys of 4 or more metals has been extremely limited. We have investigated quaternary alloys of noble and transition metals for OER by combinatorial methods. Samples were synthesized via magnetron sputtering, and a home-built scanning electrochemical system was used to screen samples based on cyclic voltammetry and electrochemical impedance spectroscopy. Data were analyzed based on a differential Tafel plot to determine the kinetics of the primary reaction. These results were then fed into various multi-target machine learning algorithms, one of which was selected for use based upon its ability to provide physically meaningful predictions in order to help identify various relationships to understand the mechanisms by which the reaction takes place. Here, we present the results of this comprehensive study.   

Novel Approaches for Synthesizing Self-Supporting Flexible Bifunctional Electrocatalysts with Hierarchical Structures and High Catalytic Activity for Rechargeable Zinc-Air Batteries

     Developing efficient bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical for advancing rechargeable zinc-air batteries. Recent advancements in electrostatic spinning technology have led to significant developments in polymer-zinc-air battery systems. This work presents two novel approaches for synthesizing self-supporting flexible bifunctional electrocatalysts with hierarchical structures and high catalytic activity by tailoring electrostatic spinning parameters. The first approach combines metal-organic frameworks with electrospinning technology to synthesize FeCoNi nanoparticles decorated N-doped carbon hierarchical networks. The FeCoNi nanoparticles are converted from Fe³⁺/Co²⁺/Ni²⁺ ions in the electrospun fibers and catalyze the pyrolysis of ZIF-67 on the fiber surface to generate reticulated carbon microfibers. The second approach harnesses the properties of organic salts in polymer solutions via electrospinning to synthesize FeCoNi flexible carbon nanofibers. These catalysts benefit from the secondary growth of FeCoNi- and N-doped carbon nanotubes on fiber surfaces, generating numerous metal-nitrogen-carbon (M-N-C) ORR active sites and FeCoNi alloy-based OER active sites. Both approaches produce bifunctional electrocatalysts with excellent ORR and OER activity, surpassing that of the existing Pt/C and RuO₂ catalysts. Rechargeable zinc-air batteries constructed with these catalysts achieve high peak power density and exceptional cycling stability, making them promising candidates for next-generation energy storage devices.   

Modeling Fast Energy Storage Reactions in RuO2 Pseudocapacitors under Realistic Conditions.

Pseudocapacitors are electrochemical devices that exhibit battery-like energy densities and supercapacitor-like power densities. Ruthenia (RuO₂) pseudocapacitor electrodes have high charge storage arising from redox reactions at the surface of the material in a liquid electrolyte. We simulate the response of RuO₂ under surface strain at various pH including interface polarization due to an applied voltage. We use the self-consistent continuum solvation (SCCS) model implemented in the Quantum-Espresso code to produce a database of free energies for several configurations of adsorbed hydrogen atoms on the electrode surface. This database is processed with grand canonical Monte Carlo sampling under various voltage conditions. These computational results elucidate the interfacial mechanisms that control the charge storage performance of RuO₂ electrodes.   

Biochar-Polymer Composite Based Electrochemical Double-Layer Capacitors

We will present our investigations on the charge storage capacity of biochar-polymer PVDF-HFP (Vinylidene Fluoride- Co-Hexafluoropropylene) composite-based electrode materials for electrochemical double-layer capacitors (EDLCs). Electrochemical double-layer capacitors EDLC devices with electrode materials having different composition ratios of Biochar to polymer were measured. Our investigations indicate the possibility of obtaining specific capacitance values of ~ 65F/g measured at 0.1 mv/s of scan rate. We will discuss how the variation of the compositional ratio (biochar to polymer) affects the EDLC properties in general considering the results obtained from various electrochemical measurements such as cyclic voltammetry (CV), Galvan static Charge-Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS).   

Gibbs ensemble Monte Carlo simulations for adsorption/desorption of natural gas mixtures in nanoporous materials to assess changes in deliverable energy during cyclic operation

Natural gas (NG) is a cleaner and cheaper fuel with a high energy–to–CO₂ emission ratio. Adsorbed Natural Gas (ANG) storage tanks, packed with a porous adsorbent, have the potential to increase the NG energy density and are being explored extensively for vehicular applications. Even after sweetening, NG is a complex mixture composed of 95% CH₄, smaller fractions of C₂H₆, C₃H₈, CO₂, N₂, and traces of higher hydrocarbons. Hence, a significant challenge in deploying ANG tanks is the poisoning of the adsorbent with the trace components of NG, and the extent of this degradation in deliverable capacity requires further understanding. Previously, mathematical modeling based on data from grand canonical Monte Carlo simulations and ideal adsorption solution theory (IAST) has been utilized to study ANG tank poisoning over multiple cycles of filling and delivery^[1],[2]. However, the assumptions of an infinite reservoir may not reflect the rapid filling required for an ANG storage tank, and IAST would not work for adsorbents with multiple adsorption sites or adsorbates that interact with each other. Therefore, we probe the degradation of the storage capacity using NpT-Gibbs Ensemble Monte Carlo (GEMC) simulations for an eight-component NG mixture and two approaches to reflect the finite reservoir during filling at the filling pressure. One approach utilizes a large system (both the amount of adsorbent and the number of gas molecules), and the other uses multiple small systems with stochastically determined gas composition. During delivery, the filled adsorbent is brought into contact with an empty gas box at the release pressure. Our results demonstrate the enrichment of higher hydrocarbons and a decrease in CH₄ deliverable capacity after multiple stages of cyclic filling/delivery, but the extent of the decrease in deliverable energy over multiple stages differs significantly from those deduced using the mathematical tank model.

Defect dynamics in isoelectronically doped MoS2 for hydrogen production

Molybdenum disulfide (MoS₂) has been widely investigated as prospective electrocatalysts for hydrogen production. MoS₂ edges have almost the same catalytic efficiency as platinum. However, the basal plane is inert. Manipulation with phases, vacancies, edges, and grain boundaries path the way to activate the basal plane. The isoelectronic doping during the chemical vapor deposition (CVD) of MoS₂ may effectively control these parameters desirably. This abstract describes the isoelectronic (W and Se) doping effect on the MoS₂ monolayer catalytic activity.

The addition of W and Se during the CVD synthesis causes the substitution of Mo and S. The Tafel slopes significantly decrease at low concentrations of W and Se defects (up to 30%), which indicates increasing efficiency of H₂ formation. High concentration of metallic and chalcogen substitution defects differently affects the catalytic efficiency. It is caused by the doping-triggered vacancies formation and phase transition. At lower doping rates, single-atom defects trigger the formation of S vacancies and the transition of the 2H phase into the metastable 1T. At high doping rates, the 1T phase transition is suppressed in W-doped samples, which is not the case for Se-doping. The DFT simulations support the defect-associated TMD’s structure changes and favorable hydrogen reaction on the doped MoS₂. Considering the interactions of cooperative effects path the way to understand the most effective TMD electrocatalyst design.   

Inexpensive green hydrogen production from aluminum-water reaction.

Aluminum has proven to be an effective, safe, and practical means of storing and generating hydrogen gas; particularly attractive when high energy density is needed, and water is readily available. This study investigates the recovery and reuse of a 5 wt.% gallium-indium eutectic used as a surface coating to disrupt the passivation layer, allowing the aluminum to spontaneously react with water. A Honda EU1000i Generator was fueled by hydrogen produced from aluminum and water, generating 400W of electricity. A hydrogen yield of 99% was achieved, with 99% of the gallium-indium liquid metal eutectic recovered and reused.   

The activity of Pd supported Pd supported SiX (X=Group-V) Single-atom catalysts for hydrogen evolution reaction.

Developing a low-cost, durable, high-performance single-atom catalyst (SAC), active for hydrogen evolution reaction (HER), is an effective strategy for energy applications. Herein, we have investigated the structural, electronic and HER catalytic activity of palladium-decorated SiX (X = Group-V) SACs within the density functional theory (DFT) framework. Strong interaction between the palladium atom and SiX nanosheets is observed, as evident from the negative value of binding energy and Bader charge transfer. Palladium modifies the electronic properties of SiX nanosheets, reducing the band gap of Pd@SiX SACs. It is observed that the Gibbs free energy (ΔG) for Pd@SiX SACs decreases as compared to pristine systems. But under the external potential the photogenerated electrons provide at pH=0, Pd@SiSb and Pd@SiBi indicate an ΔG of 0.23 and -0.22 eV, respectively. At pH=7, the best catalytic activity is shown by Pd@SiBi with a ΔG of 0.19 eV, making it active towards HER activity. This indicates the potential application of Pd@SiBi towards HER activity in the pH=0 to 7 and under the supplied external potential. Our findings may provide fruitful insights into designing and fabricating low-dimensional materials using SAC as palladium for enhanced catalytic activities.   

Catalyzing Anhydrous Proton Conduction: A Computational Workflow for Fuel Cell Materials Design

The development of materials for anhydrous proton conduction is crucial for enhancing proton exchange membrane fuel cell performance, reducing costs, and expanding operating conditions. We present a computational workflow using deep learning potentials (DPs), graph lattice models, deep learning charge density predictors, and a reactive active learning scheme to design fuel cell membrane materials. Our approach highlights that graphanol (hydroxylated graphane) conducts protons anhydrously with low diffusion barriers. Proton self-diffusion coefficients of graphanol were calculated with accurate and efficient DPs to estimate overall diffusion barriers. The sensitivity of intrinsic energy barriers to the overall diffusion barrier for proton conduction was assessed using GLMs. We discovered transient hydrogen-bonded structures (Grotthuss chains) governing proton conduction. Long-range transport occurs through the formation of new Grotthuss chains via hydroxyl group rotation. Thus, the overall diffusion barrier consists of a convolution of the intrinsic proton hopping barrier and the intrinsic hydroxyl rotation barrier. This work yielded design rules for developing advanced proton-conducting materials. Finally, we demonstrate how an efficient reactive active learning method can be used to study chemical reactions involving degradation pathways. This method is highly versatile and can be applied to many other systems to develop DPs capable of accounting for chemical reactions.   

Tuning the electrocatalytic perfomance of mixed transition-metal hydroxides for hydrogen production

Water electrolysis is considered a key technology to meet global energy demands by sustainably producing green hydrogen and oxygen fuel. Although much progress has been made to improve the effectiveness of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), the cathodic and anodic reactions respectively, the performance of electrochemical cells is still constrained by the lack of dual-selectivity and degradation of the catalytic components. Here, we investigate the performance and mechanism of multimetal catalysts serving dual functionality in both OER and HER of water electrolysis under electrochemical conditions. Using density functional theory to gain insight as the active site and mechanism, we propose that the inclusion of a minor amount of Cr increases the degeneracy of energetic states that lowers the cost of forming the O 2 p–d bond and H 1 s–d bond due to the hybridization of s, p, and d orbitals from Cr compared to Ti, V, and Mn. The implicit self-consistent continuum solvation (SCCS) model is employed to model the activity of the multimetal catalysts under an applied voltage in both alkaline and acidic conditions. This study demonstrates how tuning the amount of dopants in the nanocrystalline Fe, Co, and Ni structure is important for improving bifunctional catalytic behavior in water electrolysis.   

Acetonitrile concentration dependent ion mobility and electrochemical behavior of an ionic liquid in MXene

Ionic liquids are promising electrolytes for energy-storing devices. Even though they have high potential windows, they suffer from low conductivity because of high viscosity and are more often mixed with organic solvents. Here, we have explored the electrochemical performances and the ion dynamics of an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EmimTFSI], in the presence of acetonitrile employing electrochemical and neutron scattering measurements. A higher capacitance observed at an optimum concentration, associated with increased microscopic dynamics of cations, will be discussed.