Density functional theory calculations for the hydrogen evolution reaction in an electrochemical double layer on the Pt(111) electrode

Dispersion corrected RPBE studies of liquid water

The structure of liquid water has been addressed by ab initio molecular dynamics simulations based on density functional theory. Exchange-correlation effects have been described by the popular PBE and RPBE functionals within the generalized gradient approximation as these functionals also yield satisfactory results for metals which is important to model electrochemical interfaces from first principles. In addition, dispersive interactions are included by using dispersion-corrected schemes. It turns out that the dispersion-corrected RPBE functional reproduces liquid water properties quite well in contrast to the PBE functional. This is caused by the replacement of the over-estimated directional hydrogen-bonding in the PBE functional by non-directional dispersive interactions.

Kinetically induced irreversibility in electro-oxidation and reduction of Pt surface

A mean field kinetic model was developed for electrochemical oxidations and reductions of Pt(111) on the basis of density functional theory calculations, and the reaction mechanisms were analyzed. The model reasonably describes asymmetric shapes of cyclic voltammograms and small Tafel slopes of relevant redox reactions observed in experiments without assuming any unphysical forms of rate equations. Simulations using the model indicate that the oxidation of Pt(111) proceeds via an electrochemical oxidation from Pt to PtOH and a disproportionation reaction from PtOH to PtO and Pt, while its reduction proceeds via two electrochemical reductions from PtO to PtOH and from PtOH to Pt.

Monolayer-precision synthesis of molybdenum sulfide nanoparticles and their nanoscale size effects in the hydrogen evolution reaction

Metal sulfide-based nanostructured materials have emerged as promising catalysts for hydrogen evolution reaction (HER), and significant progress has been achieved in enhancing their activity and durability for the HER. The understanding of nanoscale size-dependent catalytic activities can suggest critical information regarding catalytic reactivity, providing the scientific basis for the design of advanced catalysts. However, nanoscale size effects in metal sulfide-based HER catalysts have not yet been established fully, due to the synthetic difficulty in precisely size-controlled metal sulfide nanoparticles. Here we report the preparation of molybdenum sulfide (MoS2) nanoparticles with monolayer precision from one to four layers with the nearly constant basal plane size of 5 nm, and their size-dependent catalytic activity in the HER. Using density functional theory (DFT) calculations, we identified the most favorable single-, double-, and triple-layer MoS2 model structures for the HER, and calculated elementary step energetics of the HER over these three model structures. Combining HER activity measurements and the DFT calculation results, we establish that the turnover frequency of MoS2 nanoparticles in the HER increases in a quasi-linear manner with decreased layer numbers. Cobalt-promoted MoS2 nanoparticles also exhibited similar HER activity trend. We attribute the higher HER activity of smaller metal sulfide nanoparticles to the higher degree of oxidation, higher Mo-S coordination number, formation of the 1T phase, and lower activation energy required to overcome transition state. This insight into the nanoscale size-dependent HER activity trend will facilitate the design of advanced HER catalysts as well as other hydrotreating catalysts.

Widely available active sites on Ni2P for electrochemical hydrogen evolution – insights from first principles calculations

A hydrogen evolution reaction barrier on Ni₂P nano wires.

A novel solid-to-solid electrocatalysis of graphene oxide reduction on copper electrode

Graphene oxide could be efficiently reduced to graphene on Cu electrode through a novel electrocatalytic solid-to-solid reaction.

Highly exposed {001} facets of titanium dioxide modified with reduced graphene oxide for dopamine sensing

Titanium dioxide (TiO2) with highly exposed {001} facets was synthesized through a facile solvo-thermal method and its surface was decorated by using reduced graphene oxide (rGO) sheets. The morphology and chemical composition of the prepared rGO/TiO2 {001} nanocomposite were examined by using suitable characterization techniques. The rGO/TiO2 {001} nanocomposite was used to modify glassy carbon electrode (GCE), which showed higher electrocatalytic activity towards the oxidation of dopamine (DA) and ascorbic acid (AA), when compared to unmodified GCE. The differential pulse voltammetric studies revealed good sensitivity and selectivity nature of the rGO/TiO2 {001} nanocomposite modified GCE for the detection of DA in the presence of AA. The modified GCE exhibited a low electrochemical detection limit of 6 μM over the linear range of 2-60 μM. Overall, this work provides a simple platform for the development of GCE modified with rGO/TiO2 {001} nanocomposite with highly exposed {001} facets for potential electrochemical sensing applications.

Tuning the MoS₂ edge-site activity for hydrogen evolution via support interactions

The hydrogen evolution reaction (HER) on supported MoS2 catalysts is investigated using periodic density functional theory, employing the new BEEF-vdW functional that explicitly takes long-range van der Waals (vdW) forces into account. We find that the support interactions involving vdW forces leads to significant changes in the hydrogen binding energy, resulting in several orders of magnitude difference in HER activity. It is generally seen for the Mo-edge that strong adhesion of the catalyst onto the support leads to weakening in the hydrogen binding. This presents a way to optimally tune the hydrogen binding on MoS2 and explains the lower than expected exchange current densities of supported MoS2 in electrochemical H2 evolution studies.

Density Functional Theory Methods for Electrocatalysis

Electrocatalysis involves catalytic reactions occurring in electrochemical systems, where bond breaking and forming on the catalyst surface are coupled with electron and ion transfer. Electrocatalytic reactions occur in fuel cells, with examples such as hydrogen oxidation, methanol oxidation, and oxygen reduction as well as in electrolysis cells, with examples such as hydrogen evolution, water splitting, and carbon dioxide reduction. Density functional theory (DFT) can be used in a similar manner to its application to non-electrochemical catalytic reactions however, additional complexities arise owing to the electrochemical nature of the catalytic interface. As in typical heterogeneous catalysis, the electrocatalyst is generally a supported nanoparticle, and all of the same challenges in developing appropriate and computationally tractable model systems (use of low-index plane surfaces or small particles as models, for example) apply to electrocatalytic systems.

Core-shell MoO3-MoS2 nanowires for hydrogen evolution: a functional design for electrocatalytic materials

We synthesize vertically oriented core-shell nanowires with substoichiometric MoO(3) cores of ∼20-50 nm and conformal MoS(2) shells of ∼2-5 nm. The core-shell architecture, produced by low-temperature sulfidization, is designed to utilize the best properties of each component material while mitigating their deficiencies. The substoichiometric MoO(3) core provides a high aspect ratio foundation and enables facile charge transport, while the conformal MoS(2) shell provides excellent catalytic activity and protection against corrosion in strong acids.