NiO Passivation in Perovskite Solar Cells: From Surface Reactivity to Device Performance.

Nonstoichiometric nickel oxide (NiO) is one of the very few metal oxides successfully used as hole extraction layer in p-i-n type perovskite solar cells (PSCs). Its favorable optoelectronic properties and facile large-scale preparation methods are potentially relevant for future commercialization of PSCs, though currently low operational stability of PSCs is reported when a NiO hole extraction layer is used in direct contact with the perovskite absorber. Poorly understood degradation reactions at this interface are seen as cause for the inferior stability, and a variety of interface passivation approaches have been shown to be effective in improving the overall solar cell performance.

From density functional theory to machine learning predictive models for electrical properties of spinel oxides.

This work focuses on predicting and characterizing the electronic conductivity of spinel oxides, which are promising materials for energy storage devices and for the oxygen evolution and oxygen reduction reactions due to their attractive properties and abundance of transition metals that can act as active sites for catalysis. To this end, a new database was developed from first principles, including band structure and conductivity properties of spinel oxides, and machine learning algorithms were trained on this database to predict electronic conductivity and band gaps based solely on the compositions. The models developed in this study are scaled from the quantum level up to a continuum conductivity model.

Cooperative Fe sites on transition metal (oxy)hydroxides drive high oxygen evolution activity in base.

Fe-containing transition-metal (oxy)hydroxides are highly active oxygen-evolution reaction (OER) electrocatalysts in alkaline media and ubiquitously form across many materials systems. The complexity and dynamics of the Fe sites within the (oxy)hydroxide have slowed understanding of how and where the Fe-based active sites form-information critical for designing catalysts and electrolytes with higher activity and stability. We show that where/how Fe species in the electrolyte incorporate into host Ni or Co (oxy)hydroxides depends on the electrochemical history and structural properties of the host material.

Enhancing Photocatalysis: Understanding the Mechanistic Diversity in Photocatalysts Modified with Single-Atom Catalytic Sites.

Surface modification of heterogeneous photocatalysts with single-atom catalysts (SACs) is an attractive approach for achieving enhanced photocatalytic performance. However, there is limited knowledge of the mechanism of photocatalytic enhancement in SAC-modified photocatalysts, which makes the rational design of high-performance SAC-based photocatalysts challenging. Herein, a series of photocatalysts for the aerobic degradation of pollutants based on anatase TiO modified with various low-cost, non-noble SACs (vanadate, Cu, and Fe ions) is reported.

NiFe-mixed metal porphyrin aerogels as oxygen evolution reaction catalysts in alkaline electrolysers.

Aerogels are a very interesting group of materials owing to their unique physical and chemical properties. In the context of electrocatalysis, the focus has been on their physical properties, and they have been used primarily as catalyst supports so far. In this work, we synthesized porphyrin aerogels containing Ni and NiFe mixed metal materials and studied them as catalysts for the oxygen evolution reaction (OER).

Transferable Classical Force Field for Pure and Mixed Metal Halide Perovskites Parameterized from First-Principles.

Many key features in photovoltaic perovskites occur in relatively long time scales and involve mixed compositions. This requires realistic but also numerically simple models. In this work we present a transferable classical force field to describe the mixed hybrid perovskite MAFAPb(BrI) for variable composition (∀, ∈ [0, 1]).

Challenges of modeling nanostructured materials for photocatalytic water splitting.

Understanding the water splitting mechanism in photocatalysis is a rewarding goal as it will allow producing clean fuel for a sustainable life in the future. However, identifying the photocatalytic mechanisms by modeling photoactive nanoparticles requires sophisticated computational techniques based on multiscale modeling. In this review, we will survey the strengths and drawbacks of currently available theoretical methods at different length and accuracy scales.

On the Interplay Between Oxygen Vacancies and Small Polarons in Manganese Iron Spinel Oxides.

Ternary spinel oxides are promising materials due to their potentially versatile properties resulting from the disorder inherent in their crystal structure. To fully unlock the potential of these materials, a deeper understanding of their electronic structures, both as pristine and defective crystals, is required. In the present work, we investigate the effects of oxygen vacancies on the electronic structure and charge transport properties of the ternary spinel oxide Mn Fe O, modeled on epitaxial thin films of the material, using density functional theory + (DFT + ).

Simulations to Cover the Waterfront for Iron Oxide Catalysis.

Hematite has been widely studied for catalytic water splitting, but the role of the interactions between catalytic sites is unknown. In this paper, we calculate the oxygen evolution reaction free energies and the surface adsorption distribution using a combination of density functional theory and Monte Carlo simulations to "cover the waterfront," or cover a wide range of properties with a simulation of the hematite surface under working conditions. First, we show that modeling noninteracting catalytic sites provides a poor explanation of hematite's slow reaction kinetics.

Selective ligand removal to improve accessibility of active sites in hierarchical MOFs for heterogeneous photocatalysis.

Metal-organic frameworks (MOFs) are commended as photocatalysts for H evolution and CO reduction as they combine light-harvesting and catalytic functions with excellent reactant adsorption capabilities. For dynamic processes in liquid phase, the accessibility of active sites becomes a critical parameter as reactant diffusion is limited by the inherently small micropores. Our strategy is to introduce additional mesopores by selectively removing one ligand in mixed-ligand MOFs via thermolysis.

The effect of interlayer stacking arrangements in two dimensional NiOOH on water oxidation catalysis.

Electrolysis of water to produce green and renewable hydrogen fuel is of great interest in the clean energy field. Water molecules can be decomposed to hydrogen and oxygen through catalysis. Catalytic materials under electrochemical operation are subject to harsh chemical environments, and as a result mechanical changes may appear in the material.

Enhanced Li-ion diffusion and electrochemical performance in strained-manganese-iron oxide core-shell nanoparticles.

Efforts to improve energy storage depend greatly on the development of efficient electrode materials. Recently, strain has been employed as an alternate approach to improve ion mobility. While lattice strain has been well-researched in catalytic applications, its effects on electrochemical energy storage are largely limited to computational studies due to complexities associated with strain control in nanomaterials as well as loss of strain due to the phase change of the active material during charging-discharging.

Bifunctional PGM-free metal organic framework-based electrocatalysts for alkaline electrolyzers: trends in the activity with different metal centers.

In order to solely rely on renewable and efficient energy sources, reliable energy storage and production systems are required. Hydrogen is considered an ideal solution as it can be produced electrochemically by water electrolysis and renewably while no pollutants are released when consumed. The most common catalysts in electrolyzers are composed of rare and expensive precious group metals.

Dipole-Induced Raman Enhancement Using Noncovalent Azobenzene-Functionalized Self-Assembled Monolayers on Graphene Terraces.

Graphene is a promising material in the field of interface science, especially for noncovalent functionalization, sensing, and for applications in catalysis and nanoelectronics. The noncovalent self-assembly of aromatic molecules on graphene promotes electronic coupling through π-π interactions that allows for quenching of the fluorescence of adsorbent molecules and the enhancement of their Raman spectra via graphene-enhanced Raman spectroscopy (GERS). Although recent work has explored the Raman enhancement on mono- and bilayer graphene, the layer dependence of both electronic phenomena (i.

Optimization of Ni-Co-Fe-Based Catalysts for Oxygen Evolution Reaction by Surface and Relaxation Phenomena Analysis.

Trimetallic double hydroxide NiFeCo-OH is prepared by coprecipitation, from which three different catalysts are fabricated by different heat treatments, all at 350 °C maximum temperature. Among the prepared catalysts, the one prepared at a heating and cooling rate of 2 °C min in N atmosphere (designated NiFeCo-N -2 °C) displays the best catalytic properties after stability testing, exhibiting a high current density (9.06 mA cm at 320 mV), low Tafel slope (72.

Pathways for charge transport through material interfaces.

Modeling charge transport across material interfaces is important for understanding the limitations of electronic devices such as transistors, electrochemical cells, sensors, and batteries. However, modeling the entire structure and full dimensionality of an interface can be computationally demanding. In this study, we investigate the validity of an efficient reduced one-dimensional Hamiltonian for calculating charge transport along interfaces by comparing to a two-dimensional model that accounts for additional charge transport pathways.

The Operando Optical Spectrum of Hematite during Water Splitting through a -BSE Calculation.

Hematite is a possible photoanode for photoelectrochemical cells (PECs) that is widely studied using density functional theory (DFT). In this paper we perform more accurate calculations of the absorption spectrum of hematite using the one-shot Green's function () and Bethe-Salpeter equation (BSE) methods, which take excited states into account and compare the spectrum to experimental data. We found a match between our calculations and the observed absorption spectra in peak locations.

Communication: Nickel hydroxide as an exceptional deviation from the quantum size effect.

The quantum size effect is a well-known fundamental scientific phenomenon. Due to quantum confinement, downscaling a system to small sizes should increase the bandgap of a solid state material. However, in this work, we present an exception: monolayers of nickel hydroxide have smaller bandgaps than their bulk analogues, due to the surface states appearing at energies within the bandgap region.

Hydrogen transfer through different crystal phases of nickel oxy/hydroxide.

Nickel hydroxide phases are common in several energy conversion devices including battery electrochemical cell electrodes. These materials have a unique layered structure that may facilitate hydrogen transfer between oxygen sites and allow using this material also for proton conducting fuel cells. In order to assess this functionality, we use Density Functional Theory+U together with the Nudged Elastic Band method to calculate minimum energy diffusion paths and hydrogen vacancy formation energies of different crystal phases of NiOOH including β-NiOOH, β-Ni(OH)2 and α-Ni(OH)2.

Operando X-Ray Absorption Spectroscopy Shows Iron Oxidation Is Concurrent with Oxygen Evolution in Cobalt-Iron (Oxy)hydroxide Electrocatalysts.

Iron cations are essential for the high activity of nickel and cobalt-based (oxy)hydroxides for the oxygen evolution reaction, but the role of iron in the catalytic mechanism remains under active investigation. Operando X-ray absorption spectroscopy and density functional theory calculations are used to demonstrate partial Fe oxidation and a shortening of the Fe-O bond length during oxygen evolution on Co(Fe)O H . Cobalt oxidation during oxygen evolution is only observed in the absence of iron.

Water Oxidation Catalysis for NiOOH by a Metropolis Monte Carlo Algorithm.

Understanding catalytic mechanisms is important for discovering better catalysts, particularly for water splitting reactions that are of great interest to the renewable energy field. One of the best performing catalysts for water oxidation is nickel oxyhydroxide (NiOOH). However, only one mechanism has been adopted so far for modeling catalysis of the active plane: β-NiOOH(01̅5).

The "Rust" Challenge: On the Correlations between Electronic Structure, Excited State Dynamics, and Photoelectrochemical Performance of Hematite Photoanodes for Solar Water Splitting.

In recent years, hematite's potential as a photoanode material for solar hydrogen production has ignited a renewed interest in its physical and interfacial properties, which continues to be an active field of research. Research on hematite photoanodes provides new insights on the correlations between electronic structure, transport properties, excited state dynamics, and charge transfer phenomena, and expands our knowledge on solar cell materials into correlated electron systems. This research news article presents a snapshot of selected theoretical and experimental developments linking the electronic structure to the photoelectrochemical performance, with particular focus on optoelectronic properties and charge carrier dynamics.

Practical Cluster Models for a Layered β-NiOOH Material.

Due to the high oxygen evolution reaction (OER) activity, stability, and abundance of NiOx materials, they are found to be promising catalysts, competitive with expensive metal oxides such as IrO₂ and RuO₂. From a theoretical point of view, studies reported in the literature so far are mostly based on density functional theory using periodic slab models for the bulk and surface of β-NiOOH, one of the active NiOx phases. However, cluster models are a valid method to investigate many aspects about structure, charge carrier transport properties, and OER activity of β-NiOOH.