Electrochemical Formation of Reactive Oxygen Species at Pt (111)—A Density Functional Theory Study

Platinum single atoms on titania aid dye photodegradation whereas platinum nanoparticles do not

The photocatalytic degradation of unwanted organic species has been investigated for decades using modified and non-modified titania nanostructures. In the present study, we investigate the co-catalytic effect of single atoms (SAs) of Pt and Pt nanoparticles on titania substrates on the degradation of the two typical photodegradation model pollutants: Acid Orange 7 (AO7) and Rhodamine B (RhB). For this, we use highly defined sputter deposited anatase layers and load them with Pt SAs at different loading densities or alternatively with Pt nanoparticles. We find that the Pt SAs have strong accelerating effects (already for a low loading density of ∼105 SAs μm-2) on the photodegradation of AO7, whereas Pt nanoparticles do hardly have an effect on the decay kinetics. The main beneficial effect of SA Pt is facilitated superoxide formation, which for SAs is significantly enhanced. Overall, the work demonstrates that Pt SA co-catalysts can have a beneficial effect not only for the well-studied use of H2 generation, but also in the photocatalytic degradation of pollutants-this is particularly the case if the degradation is dominated by a conduction band electron transfer to dissolved O2 in the solution.

A kinetic descriptor for the electrolyte effect on the oxygen reduction kinetics on Pt(111)

Proton-exchange membrane fuel cells demand efficient electrode–electrolyte interfaces to catalyse the oxygen reduction reaction (ORR), the kinetics of which depends on the energetics of surface adsorption and on electrolyte environment. Here we show an unanticipated effect of non-specifically adsorbed anions on the ORR kinetics on a Pt(111) electrode; these trends do not follow the usual ORR descriptor, that is *OH binding energy. We propose a voltammetry-accessible descriptor, namely reversibility of the *O ↔ *OH transition. This descriptor tracks the dependence of ORR rates on electrolyte, including the concentration/identity of anions in acidic media, cations in alkaline media and the effect of ionomers. We propose a model that relates the ORR rate on Pt(111) to the rate of the *O to *OH transition, in addition to the thermodynamic *OH binding energy descriptor. Our model also rationalizes different trends for the ORR rate on stepped Pt surfaces in acidic versus alkaline media.

Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments

Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the 'junctions' between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

Ab Initio Simulations of Water/Metal Interfaces

Structures and processes at water/metal interfaces play an important technological role in electrochemical energy conversion and storage, photoconversion, sensors, and corrosion, just to name a few. However, they are also of fundamental significance as a model system for the study of solid-liquid interfaces, which requires combining concepts from the chemistry and physics of crystalline materials and liquids. Particularly interesting is the fact that the water-water and water-metal interactions are of similar strength so that the structures at water/metal interfaces result from a competition between these comparable interactions. Because water is a polar molecule and water and metal surfaces are both polarizable, explicit consideration of the electronic degrees of freedom at water/metal interfaces is mandatory. In principle, ab initio molecular dynamics simulations are thus the method of choice to model water/metal interfaces, but they are computationally still rather demanding. Here, ab initio simulations of water/metal interfaces will be reviewed, starting from static systems such as the adsorption of single water molecules, water clusters, and icelike layers, followed by the properties of liquid water layers at metal surfaces. Technical issues such as the appropriate first-principles description of the water-water and water-metal interactions will be discussed, and electrochemical aspects will be addressed. Finally, more approximate but numerically less demanding approaches to treat water at metal surfaces from first-principles will be briefly discussed.

Properties of the Pt(111)/electrolyte electrochemical interface studied with a hybrid DFT-solvation approach

Self-consistent modeling of the interface between solid metal electrode and liquid electrolyte is a crucial challenge in computational electrochemistry. In this contribution, we adopt the effective screening medium reference interaction site method (ESM-RISM) to study the charged interface between a Pt(111) surface that is partially covered with chemisorbed oxygen and an aqueous acidic electrolyte. This method proves to be well suited to describe the chemisorption and charging state of the interface at controlled electrode potential. We present an in-depth assessment of the ESM-RISM parameterization and of the importance of computing near-surface water molecules explicitly at the quantum mechanical level. We found that ESM-RISM is able to reproduce some key interface properties, including the peculiar, non-monotonic charging relation of the Pt(111)/electrolyte interface. The comparison with independent theoretical models and explicit simulations of the interface reveals strengths and limitations of ESM-RISM for modeling electrochemical interfaces.

Solvated proton and the origin of the high onset overpotential in the oxygen reduction reaction on Pt(111)

For the hydrogenation of O atoms on Pt(111), protonation can be bypassed by hydrolysis as the electrode potential rises.

Interface Properties of the Partially Oxidized Pt(111) Surface Using Hybrid DFT-Solvation Models

This article reports a theoretical-computational effort to model the interface between an oxidized platinum surface and aqueous electrolyte. It strives to account for the impact of the electrode potential, formation of surface-bound oxygen species, orientational ordering of near-surface solvent molecules, and metal surface charging on the potential profile along the normal direction. The computational scheme is based on the DFT/ESM-RISM method to simulate the charged Pt(111) surface with varying number of oxygen adatoms in acidic solution. This hybrid solvation method is known to qualitatively reproduce bulk metal properties like the work function. However, the presented calculations reveal that vital interface properties such as the electrostatic potential at the outer Helmholtz plane are highly sensitive to the position of the metal surface slab relative to the DFT-RISM boundary region. Shifting the relative position of the slab also affects the free energy of the system. It follows that there is an optimal distance for the first solvent layer within the ESM-RISM framework, which could be found by optimizing the position of the frozen Pt(111) slab. As it stands, manual sampling of the position of the slab is impractical and betrays the self-consistency of the method. Based on this understanding, we propose the implementation of a free energy optimization scheme of the relative position of the slab in the DFT-RISM boundary region. This optimization scheme could considerably increase the applicability of the hybrid method.

Surface configuration and wettability of nickel(oxy)hydroxides: a first-principles investigation

This article explores the wetting behavior of β-type nickel hydroxide, β-Ni(OH)₂, and nickel oxyhydroxide, β-NiOOH, by means of first-principles calculations.