Electrochemical materials discovery and intelligence

Design and implementation of efficient and cost-effective electrochemical devices is a complex challenge. It hinges on big-data driven knowledge at the frontiers of multi-disciplinary efforts in materials discovery and design. These massive data–driven processes, however, require intensive cognitive, yet expensive systems, including human, to determine the best design decisions. A novel approach towards Artificial Intelligence (AI) and Machine Learning (ML) algorithms can overcome the complexity of selecting advanced new materials with the predictable and desired properties. Focusing on advanced electrocatalysts for CO2 conversion as a use case, we demonstrate an AI-driven “Virtual Materials Intelligence” platform (beta) for materials data management and intelligent design equipped with an advanced user interface and predictive capabilities in view of materials properties and function. The platform combines information originating from large data sets of different origins. The data storage, data analysis, and advanced analysis algorithms enable efficient and secure data flow between several different simulation and characterization activities. The cloud-based platform ultimately aims to manage all available materials databases and relevant modeling, simulation, performance, cost, and characterization data and how they can be communicated to materials fabrication and design teams

Double layer of Platinum Electrodes: Non-Monotonic Surface Charging Phenomena and Negative Double Layer Capacitance

In this study, the refined double layer model of platinum electrodes accounts for chemisorbed oxygen species, oriented interfacial water molecules and ion size effects in solution. It results in a non-monotonic surface charging relation and a peculiar capacitance vs. potential curve with a maximum and maybe negative-defined values in the potential regime of oxide-formation. &nbsp

Approaching the Self-Consistency Challenge of Electrocatalysis with Theory and Computation

This opinion piece centers around challenges involved in developing first- principles electrochemical methods. In recent years, theory and computation have become quintessential tools to navigate the parameter space that controls the activity and stability of electrocatalytic materials and electrochemical devices. Viable methods process as input details on materials structure, composition and reaction conditions. Their output includes metrics for stability and activity, phase diagrams, as well as mechanistic insights on reaction mechanisms and pathways. The core challenge, connecting input to output, is a self-consistency problem that couples the electrode potential to variables for the electronic structure of the solid electrode, solvent properties and ion distributions in the electrolyte as well as specific properties of a boundary region in between. We will discuss a theoretical framework and computational approaches that strive to accomplish this feat

Surface Configuration and Wettability of Nickel (Oxy)Hydroxides: A First-Principles Investigation

This article explores the wetting behavior of b-type nickel hydroxide, b-Ni(OH)2, and nickel oxyhydroxide, b-NiOOH, by means of first-principles calculations. Water is found to interact weakly with b-Ni(OH)2(001), but strongly with b-NiOOH(001). As unveiled with the use of ab initio molecular dynamics simulations, surface water layers at b-NiOOH(001) show a high degree of ordering correlated with a large surface polarization effect. In comparison, interfacial water at b-Ni(OH)2(001) exhibits enhanced disorder and higher mobility. The weak interaction of water with b-Ni(OH)2(001) is consistent with the small dipole moment of this surface. On the surface of b-NiOOH(001), in addition to the significantly increased surface dipole moment, unsaturated O atoms increase the number of hydrogen bonds between water molecules and the surface, resulting in strong water binding. The wettability trends found in this simulation study are consistent with experimental observations. Another theoretical observation is the increased work function of b-NiOOH(001) relative to b-Ni(OH)2(001) that agrees with experimental results reported in the literature

Unifying Theoretical Framework for Deciphering the Oxygen Reduction Reaction on Platinum

Rapid conversion of oxygen into water is crucial to the operation of polymer electrolyte fuel cells and other emerging electrochemical energy technologies. Chemisorbed oxygen species play double-edged roles in this reaction, acting as vital intermediates on one hand and site-blockers on the other. Any attempt to decipher the oxygen reduction reaction (ORR) must first relate the formation of oxygen intermediates to basic electronic and electrostatic properties of the catalytic surface, and then link it to parameters of catalyst activity. An approach that accomplishes this feat will be of great utility for catalyst materials development and predictive model formulation of electrode operation. Here, we present a theoretical framework for the multiple interrelated surface phenomena and processes involved, particularly, by incorporating the double-layer effects. It sheds light on the roles of oxygen intermediates and gives out the Tafel slope and exchange current density as continuous functions of electrode potential. Moreover, it develops the concept of a rate determining term which should replace the concept of a rate determining step for multi-electron reactions, and offers a new perspective on the volcano relation of the ORR. &nbsp

Local Impact of Pt Nanodeposits on Ionomer Decomposition in Polymer Electrolyte Membranes

Based on recent theoretical studies, we designed a multistep experimental protocol to understand the impact of environmental conditions around Pt nanodeposits on Membrane chemical degradation. The first experiment probes the local potential at a Pt microelectrode for different rates of permeation of hydrogen and oxygen gases from anode and cathode side. The subsequent degradation experiment utilizes the local conditions taken from the first experiment to analyze local rates of ionomer degradation. The rate of ionomer decomposition is significantly enhanced in the anodic H2-rich membrane region, which can be explained with the markedly increased amount of H2O2 formation at Pt nanodeposits in this region

Physical Modeling of the Proton Density in Nanopores of PEM Fuel Cell Catalyst Layers

In polymer electrolyte fuel cells, a foremost goal is to design catalyst layers with high performance at markedly reduced platinum loading. As a contribution towards this objective, we explore a simplified pore geometry to capture the impact of ionomer structure and metal charging properties on the proton density distribution and conductivity in relevant nanopores. The basic model is a cylindrical tubular pore confined by an ionomer shell and a solid platinum-coated core. The gap region between metal and ionomer is filled with water. We study how the surface charge density at the ionomer and the metal charging relation as well as geometric pore parameters affect the electrochemical performance. The density of charged side chains at the ionomer shell exerts a pronounced impact on the surface charge density at the Pt surface and thereby on the activity of the pore for the oxygen reduction reaction. The key parameter controlling the interplay of surface and bulk charging phenomena is the overlap of the Debye lengths of ionomer and metal surfaces in relation to the width of the gap. It allows distinguishing regions with weak and strong correlation between surface charge densities at ionomer shell and Pt core

Deciphering the Exceptional Performance of NiFe Hydroxide for Oxygen Evolution Reaction in Anion Exchange Membrane Electrolyzer

Hydrogen production via water electrolysis with renewable electricity as input will be crucial for the coming defossilized energy age. Herein, we report an anion exchange membrane electrolyzer using Fe-doped Ni hydroxide as anode catalyst that is on par with proton exchange membrane electrolyzers in terms of performance, 2 A cm-2 at 2.046 V and 50 °C. We found that Fe-doping stabilizes the alfa-Ni(OH)2 phase which is key to ensure the fast Ni(OH)2/NiOOH redox transition and the subsequent fast reaction between Ni3+/4+ and the electrolyte (OH-), resulting in the excellent oxygen evolution reaction activity of Fe-doped Ni hydroxide. Spin-polarized DFT+U computations reveal that the local arrangement of Fe3+ with Ni3+/4+ plays a crucial role in enabling the high OER activity on (001) facet of this anode catalyst