Theoretical investigation on potential of zero free charge of (111) and (100) surfaces of Group 10 and 11 metals

The potential of zero free charge (PZFC) value is a crucial parameter in electrochemistry. However, the evaluations of PZFC have traditionally been difficult. To overcome this challenge, we applied a hybrid solvation method that incorporates, both an explicit water layer next to the metal surface and an implicit water layer, combined with density functional theory (DFT) to simplify the PZFC evaluation. Using the (111) and (100) surfaces of Group 10 and 11 metals as model systems, we calculated their PZFC values, which showed excellent agreement with the reported data. This great match validates the accuracy and reliability of our theoretical approach. Notably, we observed that the surface structure and the orientation of water molecules have a significant influence on the PZFC values of the metals. Our study, therefore, paves the way for efficiently and accurately calculating the PZFC values of materials, which can greatly benefit their practical applications.Comment: 26 pages, 7 figures, paper contribution to thesi

Affordable Double-Reference Approach for Simulating Electrified Pt(111)/Water Interfaces

The electrified solid-liquid interface plays an essential role in many renewable energy-related applications, including hydrogen production and utilization. Limitations in computational modelling of the electrified solid-liquid interface have held back the understanding of its properties at the atomic-scale level. In this study, we applied the grand canonical density functional theory (GC-DFT) combined with a hybrid implicit/explicit solvation model to reinvestigate the widely studied electrified platinum-water interface affordably. This GC-DFT method was validated by successfully reproducing the experimental potential of zero charge (PZC) of the Pt(111)-water interface. The calculated capacitances of the Pt(111)-water interface over the applied bias potential closely match the experimental and previous theoretical data from expensive ab-initio molecular dynamics simulations. The structural analysis of the interface models reveals that the applied bias potential can significantly affect the Pt(111)-water atomic interface configurations. The orientation of the water molecules next to the Pt(111) surface is vital for correctly describing the PZC and capacitance. Additionally, our GC-DFT results confirm that the absorption of the hydrogen atom under applied bias potential can significantly affect the electrified interfacial properties. The developed affordable GC-DFT approach, therefore, offers an efficient and accurate means to enhance the understanding of electrified solid-liquid interfaces.Comment: 24 pages, 7 figures, supporting information, still under revie

Theoretical understanding of the properties of stepped iron surfaces with van der Waals interaction corrections

The stepped surfaces in nanoscale zero-valent iron (nZVI) play an essential role for environmental application. However, there is still currently a deficiency in the atomic understanding of stepped surface properties due to the limitation of the computational methodology. In this study, stepped Fe(210) and (211) surfaces were theoretically investigated using density functional theory (DFT) computations in terms of the flat Fe(110) surface. Our results suggest that the consideration of van der Waals (vdW) interaction correction is beneficial for the DFT study on Fe-based systems. The DF-cx method is found to be the most promising vdW correction method. The DF-cx results reveal that the stepped Fe(210) and Fe(211) surfaces experience significant surface relaxation and abnormal trends in their work function. Their electronic properties and reactivities of the surface atoms are strongly affected by the Fe coordination numbers and the strong adsorption strengths of oxygen on the surfaces are dependent on both the coordination number of the adsorbed atoms and the geometry of the adsorption sites.</p

The Role of Steps on Silver Nanoparticles in Electrocatalytic Oxygen Reduction

Hydrogen fuel cell technology is an essential component of a green economy. However, it is limited in practicality and affordability by the oxygen reduction reaction (ORR). Nanoscale silver particles have been proposed as a cost-effective solution to this problem. However, previous computational studies focused on clean and flat surfaces. High-index surfaces can be used to model active steps presented in nanoparticles. Here, we used the stable stepped Ag(322) surface as a model to understand the ORR performance of steps on Ag nanoparticles. Our density functional theory (DFT) results demonstrate a small dissociation energy barrier for O2 molecules on the Ag(322) surface, which can be ascribed to the existence of low-coordination number surface atoms. Consequently, the adsorption of OOH* led to the associative pathway becoming ineffective. Alternatively, the unusual dissociative mechanism is energetically favored on Ag(322) for ORR. Our findings reveal the importance of the coordination numbers of active sites for catalytic performance, which can further guide electrocatalysts’ design.</p

The impact of metal dopants on the properties of nZVI: a theoretical study

The substitution of Fe with metal dopants shows potential for enhancing the wastewater remediation performance of nanoscale zero-valent iron (nZVI). However, the specific roles and impacts of these dopants remain unclear. To address this knowledge gap, we employed density functional theory (DFT) to investigate metal-doped nZVI on stepped surfaces. Four widely used metal dopants (Ag, Cu, Ni, and Pd) were investigated by replacing Fe atoms at the edge of the stepped surface. Previous research has indicated that these Fe atoms exhibit chemical reactivity and are vulnerable to water oxidation. Our DFT calculations revealed that the replacement of Fe atoms on the edge of the stepped surface is energetically more favorable than that on the flat Fe(110) surface. Our results shed light on the effects of metal dopants on the surface properties of nZVI. Notably, the replacement of Fe atoms with a metal dopant generally led to weaker molecular and dissociated water adsorption across all systems. The results from this study enhance our understanding of the complex interplay between dopants and the surface properties of nZVI, offering theoretical guidance for the development and optimization of metal-doped nZVI for efficient and sustainable wastewater remediation applications

β-Arsenene Monolayer : A Promising Electrocatalyst for Anodic Chlorine Evolution Reaction

Materials innovation plays an essential role to address the increasing demands of gaseous chlorine from anodic chlorine evolution reaction (CER) in chlor-alkali electrolysis. In this study, two-dimensional (2D) semiconducting group-VA monolayers were theoretically screened for the electrochemical CER by means of the density functional theory (DFT) method. Our results reveal the monolayered β-arsenene has the ultralow thermodynamic overpotential of 0.068 V for CER, which is close to that of the commercial Ru/Ir-based dimensionally stable anode (DSA) of 0.08 V @ 10 mA cm−2 and 0.13 V from experiments and theory, respectively. The change of CER pathways via Cl* intermediate on 2D β-arsenene also efficiently suppresses the parasitical oxygen gas production because of a high theoretical oxygen evolution reaction (OER) overpotential of 1.95 V. Our findings may therefore expand the scope of the electrocatalysts design for CER by using emerging 2D materials.</p

TMN4 complex embedded graphene as efficient and selective electrocatalysts for chlorine evolution reactions

In the industrial large-scale chlor-alkali process, the electrocatalytic chlorine evolution reaction (CER) is a crucial half anodic reaction. However, the concomitant oxygen evolution reaction (OER) is unavoidable by using the noble metal-based dimensionally stable anodes (DSAs) as CER benchmark catalysts. Through purposely screening six TMN4 complexes embedded graphene with the demonstrated low performance of OER, our density functional theory (DFT) results predict that NiN4 complex embedded graphene (NiN4@G) can efficiently catalyse the CER. This single-atom catalyst (SAC) shows superior CER activity with the ultralow thermodynamic overpotential of 0.014 V via the Cl* intermediate instead of the formation of the ClO*. Moreover, its high theoretical overpotential of OER inherently promotes the selectivity of chlorine evolution. The analyses of the bonding mechanism between TM and Cl atoms reveal that their electrostatic attraction forces can be a good descriptor for the discovery of high-performance CER electrocatalysts. Our findings may broaden the scope of CER catalysts design beyond DSAs with the maximized metal atom utilization.</p

Low-Dimensional Metal-Organic Frameworks with High Activity and Selectivity toward Electrocatalytic Chlorine Evolution Reactions

Chlorine gas plays a paramount role in modern industrial chemistry and is one of the most basic chemicals produced by the electrolysis of brine solution. In the past decades, the dimensionally stable anode (DSA) made of RuO2is the benchmark catalyst for the chlorine evolution reaction (CER) with high activity. However, the drawbacks of the DSA, such as high cost and inferior selectivity, demand the development of low-cost and efficient electrocatalysts for CER. Herein, three low-dimensional Fe/Co/Ni-dithiolene metal-organic frameworks (MOFs) were systematically investigated using the density functional theory. Our calculation results predict that Ni-based dithiolene MOF can efficiently catalyze the CER with a low thermodynamic overpotential of 0.049 V via the Cl∗ intermediate. The electronic resonance structure of [Ni2+(L•-)(L2-)]-in the Ni-based dithiolene MOF leads to the electron transfer first from S atoms in ligands to Ni cations to achieve a stable electronic configuration, which leads to the most desirable Ni-Cl interaction strength for CER. Moreover, the selectivity to Cl2generation is due to its high thermodynamic overpotential of oxygen evolution reaction. Our findings may, therefore, accelerate CER catalyst discoveries beyond DSAs with the optimized electronic structures.</p

Revisiting the Electrified Pt(111)/Water Interfaces through an Affordable Double-Reference Ab Initio Approach

The electrified solid–liquid interface plays an essential role in many renewable energy-related applications, including hydrogen production and utilization. Limitations in computational modeling of the electrified solid–liquid interface have held back the understanding of its properties at the atomic-scale level. In this study, we applied the grand canonical density functional theory (GC-DFT) combined with a hybrid implicit/explicit solvation model to reinvestigate the widely studied electrified platinum-water interface affordably. The calculated double-layer capacitances of the Pt(111)–water interface over the applied bias potential closely match the experimental and previous theoretical data from expensive ab initio molecular dynamics simulations. The structural analysis of the interface models reveals that the applied bias potential can significantly affect the Pt(111)–water atomic interface configurations. The orientation of the water molecules next to the Pt(111) surface is vital for correctly describing the potential of zero charge (PZC) and capacitance. Additionally, the GC-DFT results confirm that the absorption of the hydrogen atom under applied bias potential can significantly affect the electrified interfacial properties. The presented affordable GC-DFT approach, therefore, offers an efficient and accurate means to enhance the understanding of electrified solid–liquid interfaces