Basal Plane Surface Research Articles

Measuring the Surface Energy of Nanosheets by Emulsion Inversion.

Solution-processed nanomaterials can be assembled by a range of interfacial techniques, including as stabilizers in Pickering emulsions. Two-dimensional (2D) materials present a promising route toward nanosheet-stabilized emulsions for functional segregated networks, while also facilitating surface energy studies. Here, we demonstrate emulsions stabilized by the 2D materials including the transition metal carbide MXene, titanium carbide (Ti3C2T x ), and develop an approach for in situ measurement of nanosheet surface energy based on emulsion inversion. This approach is applied to determine the influence of pH and nanosheet size on surface energy for MXene, graphene oxide, pristine graphene, and molybdenum disulfide. The surface energy values of hydrophilic Ti3C2T x and graphene oxide decrease significantly upon protonation of usually dissociated functional groups, facilitating emulsion stabilization. Similarly, pristine graphene and molybdenum disulfide increase in surface energy when their surface functional groups are deprotonated under basic conditions. In addition, the surface energies of these pristine materials are correlated with nanosheet size, which allows for the calculation of the basal plane and edge surface energies of pristine nanosheets. This understanding of surface energies and control of emulsion inversion will allow design of emulsion-templated structures and surface energy studies of a wide range of solution-processable nanomaterials.

Selective Covalent Basal Plane Modification as a Probe of Hydroxide Ion Conduction Pathways in Magnesium Aluminum Layered Double Hydroxides.

Understanding ionic conduction in layered double hydroxides (LDHs) is a crucial step towards utilizing them as solid, hydroxide ion-conducting electrolytes in energy conversion applications. We selectively modified the interlayer and external surfaces of MgAl LDHs with tris(hydroxymethyl)aminomethane (TRIS) ligands. By adjusting the concentration of the TRIS surface modifier, the LDH basal plane surfaces could be functionalized everywhere (internally and externally) or only externally. External modification resulted in loss of OH-conductivity compared to pristine LDHs, confirming that external platelet surfaces are the primary ion conduction pathway.

Tritium storage and release mechanism in nuclear graphite using first-principles combined thermal desorption theory

Nuclear graphite (NG) is widely applied in nuclear facilities, and its strong interaction with tritium is an essential factor for tritium transport behavior in various reactors and the treatment of radioactive NG waste. Given that NG is a polycrystalline and porous material, interactions between tritium and NG exist in various microstructures, including graphite edges, graphene basal planes, and amorphous structures. In this study, density functional theory which is integrated in Vienna ab initio simulation package (VASP) was combined with thermal desorption theory to elucidate the underlying mechanism of hydrogen isotope storage corresponding to the experimentally observed desorption peaks in NG. The four desorption temperature peaks, ranging from low to high, were mainly attributed to hydrogen isotope desorption from the graphite basal plane surface, amorphous carbon surface, unsaturated armchair and zigzag edges, respectively. The interaction between hydrogen isotopes and carbon nanostructures provides deeper insights into the understanding of tritium enrichment on the NG surface, which is primarily attributed to the adsorption of tritium on graphite basal plane-like surfaces at relatively low temperatures. This study provides a practical method to bridge the gap between the atomic binding structure and desorption temperature peaks from a kinetic perspective, providing insights into temperature-dependent hydrogen desorption in typical carbon structures and deepening our understanding of tritium transport behaviors in advanced nuclear energy systems.

A novel insight of interaction mechanism of carboxymethyl cellulose with talc surface: A combined molecular dynamic simulation and DFT investigation

Separation of talc from sulfide minerals through adding depressor in flotation field is very necessary, while the interaction of depressor on the surface of talc still needs to be further explained. Here, a typical depressor, carboxymethyl cellulose (CMC), interacted with talc surface was deeply investigated from atomic structure and surface hydration though molecular dynamic simulation (MDs) and density functional theory (DFT) calculation. MDs was applied on investigating adsorption behaviors of CMC on basal and edge plane of talc in aqueous solutions, and DFT was used for studying the interacted orbitals and charge transfer. It was found that adsorption of CMC on surface of edge plane was stronger than that on the surface of basal plane due to the enhanced interaction of polar group on the edge plane and the dragged water molecules. Interactions existed between H atoms in CMC and O atoms in edge plane, between O atoms in CMC and Si, Mg atoms in edge plane. The strong interacted water molecules dragged CMC close to the surface, thus to strengthen the binding of CMC and edge plane of talc. Furthermore, the hydration shell on the basal and edge plane of talc was investigated for explaining the phenomenon. Therefore, our work gave a new insight into the microscopic interaction between talc and CMC, thus to guide the actual application.

Rational design of redox active amorphous Ni-Mn phosphate anchored on vertical graphene nanohills (VGNHs) for solid-state energy storage device

Transition metal phosphates (TMPs) have generated a lot of attention due to their high power and energy potential. However, pristine TMPs materials have sluggish electrode kinetics limiting their practical application. In this study, a sustainable electrochemical deposition approach has been employed for the facile fabrication of amorphous nickel-manganese phosphate (VG-NMP series) nanostructure on vertical graphene nanohills (VGNHs) covered carbon cloth (CC) substrate. Among as-prepared electrodes, the VG-NMP-4 electrode showed optimal electrochemical characteristics. The high specific capacity of VG-NMP-4 was calculated to be 1068 C g−1 (5.14 F cm−2) at a current density of 3 A g−1 and maintained 97 % capacity for 5000 cycles, which outperformed previously reported TMPs-based electrode materials. The enhanced charge storage capability of VG-NMP was mainly due to the dense edge planes of VGs and many gaps for electrolyte penetration because the exposed edge planes have larger areas than the basal plane surface, due to the synergistic effect between Ni and Mn metal ions. The VG-NMP-4 was further utilized as the cathode and anode in the PVA-KOH gel electrolyte for constructing a symmetric solid-state (SSS) supercapacitor. This SSS device offers great durability of 94 % over 5000 cycles and a supreme energy density of 106.8 Wh kg−1 at a power density of 0.751 kW kg−1. This excellent performance suggests that the amorphous Ni-Mn phosphate@VGNHs-CC nanostructured electrode material would be a promising choice for energy storage appliances.

Microfluidic-Assisted Alignment of Graphene Nanosheets for Microfiber Formation

Recently, our lab developed graphene oxide microfibers for ultrasensitive neurochemical detection with fast-scan cyclic voltammetry (FSCV). Graphene-fiber microelectrodes provide a significant advance over traditional carbon-fiber microelectrodes due to their resistance to detrimental fouling, fast electron transfer kinetics, and frequency independent behavior. Despite our recent advancement, there still exists a gap in our understanding of how specific changes in the carbon chemical structure influences adsorption and interaction of various neurochemicals at the surface. Understanding the extent to which the carbon chemical structure influences electrochemical detection is critical for designing tailor-made electrodes for ultrasensitive analyte detection. From a molecular level point-of-view, the graphene sheet consists of two regions with different structure: i) the basal plane, consisting of conjugated sp2 hybridized carbon atoms, and characterized by an atomic flatness and low defect density; and ii) the edge plane, that forms sp3 sites with a high level of defects and a variety of functional groups and dangling bonds. It is generally believed that the electrochemical properties of the basal and edge plane are significantly different, however, there has been debate concerning the electrochemical activity at the basal and edge plane. The conventional consensus is that electron transfer kinetics is faster on the edge plane in comparison with the basal plane sites, while the opposite barrier of this debate provides evidence for fast electron transfer at pristine basal plane. Moreover, how these factors influence neurochemical detection, particularly at rapid scan rates, is still lacking due to the necessity of using microelectrodes with FSCV. To date, most studies analyzing the influence of basal vs. edge plane surfaces on electrochemical detection have used macroelectrodes like highly ordered pyrolytic graphite (HOPG) which are not amenable to FSCV detection due to the large capacitive currents obtained at macroelectrodes at scan rates consisting of hundreds of volts per second. Therefore, to address this existing knowledge gap in understanding how edge vs. basal planes influence subsecond neurochemical detection, the ability to develop microelectrodes with controlled surfaces is crucial. Here, I will discuss our labs latest effort in developing graphene oxide microfibers with controllable nanosheet alignment to study the influence of basal vs. edge plane availability on neurochemical detection at rapid scan rates. To assist in nanosheet alignment, we use microfluidic channels to assist in fluid-driven control of nanosheet orientation. Using microfluidics to help develop highly controllable electrode materials provides a critical advance in our ability to develop novel carbon surfaces for detection.

Understanding and Preventing Lubrication Failure at the Carbon Atomic Steps.

Two-dimensional (2D) lamellar materials are normally capable of rendering super-low friction, wear protection, and adhesion reduction in nanoscale due to their ultralow shear strength between two basal plane surfaces. However, high friction at step edges prevents the 2D materialsfrom achieving super-low friction in macroscale applications and eventually leads to failure of lubrication performance. Here, taking graphene as an example, the authors report that not all step edges are detrimental. The armchair (AC) step edges are found to have only a minor topographic effect on friction, while the zigzag (ZZ) edges cause friction two orders of magnitude larger than the basal plane. The AC step edge is less reactive and thus more durable. However, the ZZ structure prevails when step edges are produced mechanically, for example, through mechanical exfoliation or grinding of graphite. The authors found a wayto make the high-friction ZZ edge superlubricious by reconstructing the (6,6) hexagon structure to the (5,7) azulene-like structure through thermal annealing in an inert gas environment. This will facilitate the realization of graphene-based superlubricity over a wide range of industrial applications in which avoiding the involvement of step edges is difficult.

Spark plasma sintering behavior and structural stability of 2D- WS2 nanosheets

The sintering behavior and structural stability of two-dimensional (2D) WS2 nanosheet powder under high-temperature pressure-assisted spark plasma sintering (SPS) were investigated. Transformation of the 2D particle morphology to coarse WS2 platelets was observed during sintering at a higher temperature of and above 1000 oC. Particle coarsening was caused by diffusion bonding of multiple 2D-WS2 nanosheet particles on the basal plane surface. Consolidation of the 2D-WS2 nanosheet particles at lower sintering temperatures primarily involved particle-particle interlocking and limited particle-particle diffusion bonding. About 94% of the theoretical density was achieved without any sintering additives on SPS at 1200 oC. The WS2 stoichiometry was retained even at 1200 °C with no indication of any thermal degradation. A fraction of the hexagonal 2H-type structure of the 2D-WS2 transformed to rhombohedral 3R phase during SPS at and above 800 °C. The as-sintered 2D-WS2 showed a low coefficient of friction in the range of 0.06–0.1. The observed tribological behavior was correlated with its thermo-mechanical properties and sintering characteristics at different temperatures.

A comparative study of biopolymer adsorption on model anisotropic clay surfaces using quartz crystal microbalance with dissipation (QCM-D)

Mitigation of colloid clay particles is critical during flotation and flocculation processes in mineral processing. Most organic and inorganic mitigation reagents have negative impacts on the environment and human health; therefore, biologically derived substances have been attracting attention as alternative reagents. Given the anisotropic nature of clay surfaces, it is imperative to understand reagent adsorption on the individual edge and basal plane surfaces of clays. Quartz crystal microbalance with dissipation (QCM-D) was used in this study to determine the adsorption characteristics of three biopolymers (the protein-based biopolymer, lysozyme, and protein and polysaccharide-based oligomers; protamine and pectin) on model surfaces of the anisotropic edge and basal planes of the clays (e.g., kaolinite and serpentine). SiO2 sensor representing the tetrahedral basal plane, Al2O3 and Mg(OH)2 representing the octahedral basal planes, AlSiO and MgSiO representing the edge faces of clays were used as model surfaces of clay minerals. For kaolinite, protamine adsorbed preferentially on the silica (SiO2) tetrahedral surface at pH 7 and on the alumina (Al2O3) surface at pH 10. Protamine adsorbed primarily on magnesium hydroxide (Mg(OH)2), representative of serpentine, at pH 7 and 10. Lysozyme adsorbed preferentially and irreversibly on the edge basal plane surfaces of both clays at pH 10, while it showed a higher affinity for octahedral surfaces (alumina and magnesium hydroxide) at pH 7. In contrast, pectin adsorbed strongly on the magnesium hydroxide, representative of the basal plane surface of serpentine. An adsorption study revealed that electrostatic attraction and/or hydrogen bonding mechanisms contributed to the adsorption of biopolymers on clay surfaces. This investigation provides a fundamental and practical understanding of biopolymer interactions with clay surfaces during selective flotation and flocculation.

Highly Sensitive NO2 Detection by TVS-Grown Multilayer MoS2 Films

Two-dimensional layered materials have been investigated for sensor applications over the last decade due to their very high specific surface area and excellent electrical characteristics. Although grain boundaries are inevitably present in polycrystalline-layered materials used for real applications, few studies have investigated their effects on sensing properties. In this study, we demonstrate the growth of two distinct MoS2 films that differ in grain size by means of chemical vapor deposition (CVD) and thermal vapor sulfurization (TVS) methods. Transistor-based sensors are fabricated using these films, and their NO2 sensing properties are evaluated. The adsorption behavior of NO2 on MoS2 is considered in terms of the Langmuir isotherm, and the experimental results can be well fitted by the equation. The CVD-grown film exhibits electrical properties 1–2 orders of magnitude superior to those of the TVS-grown one, which is attributed to the large grain size of the CVD-grown film. In contrast, the sensitivity to NO2 is unexpectedly found to be higher in the TVS-grown film and is of the same order of a previously reported record value. Transmission electron microscopy observations suggest that the TVS-grown film consists of multiple rotationally oriented grains that are connected by mirror twin grain boundaries. Theoretical calculation results reveal that the adsorption of NO2 on the grain boundary that we modeled is equal to that on the ideal basal plane surface of MoS2. In addition, the porous structure in the TVS-grown film may also contribute to enhancing the sensor response to NO2. This study suggests that a highly sensitive MoS2 sensor can also be fabricated by using a polycrystalline film with small grain size, which can possibly be applied to other two-dimensional materials.

Effect of structural properties of green rusts on phosphate fixation and implication for eutrophication remediation

• A Fe(II)/Fe(III) ratio of 5/1 resulted in the maximum phosphate adsorption by GRs. • Phosphate anions exchange with Cl − or SO 4 2− anions in GRs. • Phosphate gets fixed on the basal plane and lateral surface of GRs. • The interlayered Cl − or SO 4 2− have little influence on the phosphate adsorption. • The maximum phosphate adsorption efficiency by GRs was observed a near-neutral pH. As mixed-valent iron(hydr)oxides green rusts (GRs) are widely found in natural and anthropic phosphate removal processes. Effect of structural properties of GRs on phosphate adsorption is rarely studied. It is found that a Fe(II)/Fe(III) ratio of 5/1 resulted in the maximum phosphate adsorption by GRs interlayered with chloride or sulfate anions. Phosphate anions exchange with chloride or sulfate anions in GRs and then get fixed on the basal plane and lateral surface of GRs. The interlayered chloride or sulfate anions have little influence on the phosphate adsorption by GRs. The phosphate adsorption efficiency by GRs was almost constant when pH increasing from 5.5 to 7.5, but decreased when pH further increased to 9.5. Revealing the relationship between the structural properties of GRs and their phosphate adsorption performance deepen our understanding of the fate and transformation of iron (hydr)oxides and phosphate in both natural and engineered environments.

Nanoscale Electrochemistry Study Using SECCM Option of Park Systems

Scanning electrochemical cell microscopy (SECCM) is a nanoelectrochemical scanning probe technique that creates a confined electrochemical cell (droplet) via meniscus contacting the surface by employing an electrolyte filled micropipette containing quasi-reference counter electrode(QRCE).[1] It is particularly useful to investigate the heterogeneity, or local electrochemical properties of the electrode surfaces by direct mapping the electroactivity with nanoscale resolution.In this study, the electrochemically reversible [Ru (NH3)6]3+/2+ electron transfer process at a highly ordered pyrolytic graphite (HOPG) surface was recorded using Park NX12 AFM system. A single barrel glass nanopipette with Ag/AgCl inserted as QRCE was utilized. Using previous successful experience in commercializing pipette-based electrochemical microscopy,[2] Park Systems’ hardware and software enables localized nanoscopic cyclic voltammetry measurements conducted at each pixel each time the meniscus contacts the surface. Thus, a spatially resolved surface electroactivity mapping of HOPG at various scan rates were created with high-throughput at the micro-/nanoscale. The difference in electrochemical activity measured at the edge plane relative to the basal plane surface was shown.This work demonstrates that Park Systems’ commercial SECCM option is promising for quantitative electroanalysis at the nanoscale, with potential applications in energy storage (battery) studies and corrosion research. [1] Gao, R., Edwards, M. A., Qiu, Y., Barman, K., & White, H. S. (2020). Visualization of Hydrogen Evolution at Individual Platinum Nanoparticles at a Buried Interface. Journal of the American Chemical Society. [2] Shi, W., Goo, D., Jung, G., Pascual, G., Kim, B., & Lee, K. Simultaneous Topographical and Electrochemical Mapping using Scanning Ion Conductance Microscopy–Scanning Electrochemical Microscopy (SICM-SECM). Figure 1

Investigating the effect of edge and basal plane surface functionalisation of carbonaceous anodes for alkali metal (Li/Na/K) ion batteries

Alkali metal ion batteries are instrumental in the widespread implementation of electric vehicles, portable electronics, and grid energy storage. From experimental characterisation of hard carbons, these carbon anodes were shown to contain a variety of functional groups. Through density functional theory simulations, the effect of functional groups (O, OH, NH2, and COOH) on edges and basal plane surfaces of carbonaceous materials on the adsorption of lithium, sodium, and potassium are investigated. These simulations show that the functionalisation of H-terminated edges and curved surfaces rather than basal planes is more energetically favourable and thus more likely to be present. Comparison of experimental FTIR and computational vibrational frequency analysis confirmed the occurrence of the investigated functional groups (O, OH, NH2, and COOH) in the synthesised hard carbon materials. Metal adsorption on the functionalised models showed that adsorption energies were stronger on the functionalised basal plane in comparison to the functionalised edge sites and contribute to the metal ion immobilization and consequent irreversible capacity loss. The metal adsorption on the curved surface was further improved by the addition of functional groups, benefitting the initial lithiation/sodiation/potassiation of the carbon anode. Hence, the morphology of the functionalised carbon systems plays an important role in the charge/discharge performance of carbonaceous anodes.

Insights into graphene oxide interaction with human serum albumin in isolated state and in blood plasma

The interactions of graphene oxide (GO), a 2-dimensional nanomaterial with hydrophilic edges, hydrophobic basal plane and large flat surfaces, with biological macromolecules, are of key importance for the development of novel nanomaterials for biomedical applications. To gain more insight into the interaction of GO flakes with human serum albumin (HSA), we examined GO binding to HSA in its isolated state and in blood plasma. Calorimetric data reveal that GO strongly stabilizes free isolated HSA against a thermal challenge at low ionic strength, indicating strong binding interactions, confirmed by the drop in ζ-potential of the HSA/GO assemblies compared to bare GO flakes. However, calorimetry also revealed that the HSA-GO molecular interaction is hampered in blood plasma, the ionic strength being particularly important for the interactions. Molecular modelling calculations are in full concert with these experimental findings, indicating a considerably higher binding affinity for HSA to GO in its partially unfolded state, characteristic to low-ionic-strength environment, than for the native protein conformation, observed under physiological conditions. Therefore, for the first time we demonstrate an impeded interaction between HSA and GO nanoflakes in blood plasma, and suggest that the protein is protected from the plausible toxic effects of GO under native conditions.

CeO2-Based Two-Dimensional Layered Nanocomposites Derived from a Metal-Organic Framework for Selective Electrochemical Dopamine Sensors.

In this work, we demonstrate the incorporation of two-dimensional (2D) layered materials into a metal–organic framework (MOF) derived from one-dimensional (1D) cerium oxide (CeO2) for the electrochemical detection of dopamine. Ce-MOF was employed as a sacrificial template for preparing CeO2 with 2D materials by the pyrolysis process. The influence of the pyrolysis temperature was studied to achieve a better crystal structure of CeO2. Siloxene improved the dopamine sensing performance of CeO2 compared with graphitic carbon nitride (g-C3N4) due to the basal plane surface oxygen and hydroxyl groups of 2D siloxene. Under optimal conditions, the fabricated CeO2/siloxene electrode exhibited a detection limit of 0.292 μM, with a linear range from 0.292 μM to 7.8 μM. This work provides a novel scheme for designing the CeO2 material with siloxene for excellent dopamine sensors, which could be extended towards other biosensing applications.

The effect of sodium hydrosulfide on molybdenite flotation in seawater and diluted seawater

Seawater is used in copper-molybdenum flotation plants when fresh water resources are limited. To minimize the negative effect of process seawater on molybdenite flotation, diluting process seawater with fresh water is a common practice. This study was designed to identify whether the dilution of process seawater in copper-molybdenum flotation plants benefits molybdenite flotation where NaHS is added to depress chalcopyrite. Seawater was prepared based on the concentrations of salts in the process seawater used in a copper-molybdenum flotation plant, and diluted with different proportions of de-ionized water. The concentrations of NaHS chosen to test in molybdenite flotation were determined by conducting chalcopyrite flotation to depress chalcopyrite. It was found that the concentration of NaHS which maximumly depressed chalcopyrite also depressed molybdenite to some extent in both seawater and diluted seawater. Water chemical equilibrium calculation, Cryo-XPS analysis and SEM measurement indicated that the depression mechanisms of NaHS on molybdenite were different in seawater and diluted seawater. Significant dilution of seawater weakened the buffer effect of seawater on pH and raised the pH in flotation significantly after the addition of NaHS so that Mg(OH)2 and CaCO3 precipitates formed to depress molybdenite. Insignificant dilution of seawater had little effect on flotation pH after the addition of NaHS, but the adsorption of HS− and the formation of SO42− on micro-edges of basal plane surfaces of molybdenite at a high NaHS concentration decreased the hydrophobicity of the basal plane surfaces, leading to reduced molybdenite flotation recovery.

Direct-space-self-consistent-phonon treatment of monolayer structures and dynamics.

Computations, which would have been intractable just a few years ago, are now possible on desktop workstations. Such is the case for the application of the Self-Consistent-Phonon (SCP) approximation to large monolayer clusters on structured surfaces, combining a SCP approach to the system dynamics with a random walk approach to finding the optimum positions of the adsorbed atoms. This combination of techniques enables the investigation of the stability, structure, and dynamics of incommensurate adsorbed monolayers at low temperatures. We refer to this approach as the Direct-Space-Self-Consistent-Phonon framework. We present the application of this framework to the study of rare-gas and molecular hydrogen adsorbates on the graphite basal-plane surface and (for xenon) the Pt(111) surface. The largest cluster size consists of 4096 particles, a system that is large enough to examine incommensurate phases without significant adverse boundary effects. The existence of "pseudo-gaps" in the phonon spectrum of nearly commensurate monolayers is demonstrated, and the implication of such "pseudo-gaps" for the determination of the location of any commensurate ↔ incommensurate phase transition is explored. The stability of striped incommensurate structures vs hexagonal incommensurate structures is examined. The inherent difficulties of using this approach for the highly quantum monolayer solids is shown to generate some particular problems. Nevertheless, we demonstrate that this approach to the stability, structure, and dynamics of quantum monolayer solids is a very useful tool in the theorist's arsenal. By implication, this approach should also be useful in the study of adsorption on graphene and carbon nanotubes at low temperatures.

The effect of sodium hydrosulfide on molybdenite flotation as a depressant of copper sulfides

Depressing copper sulfides using sodium hydrosulfide (NaHS) in the flotation of molybdenite is a common practice. However, the effect of NaHS on the flotation of molybdenite is not clear despite a number of studies. In this study, the effect of NaHS concentrations which depressed the flotation of chalcopyrite on the flotation of molybdenite of different particle sizes was investigated. It was found that molybdenite flotation was promoted at a low NaHS concentration. A high NaHS concentration only reduced the flotation kinetics slightly without affecting the final flotation recovery. The effect of NaHS on the flotation of smaller molybdenite particles was more significant. Cryo-XPS analysis was then carried out to understand the underpinning mechanism. It was evident that the flotation behavior of molybdenite in the presence of NaHS was determined by the reactions of NaHS on the edge plane surface of molybdenite. At a low NaHS concentration, NaHS adsorbed on the edge plane surface and formed hydrophobic species such as elemental sulfur and polysulfide. At a high NaHS concentration, the hydrophobic species disappeared with more HS− adsorbed. At both low and high NaHS concentrations, NaHS did not adsorb on the basal plane surface of molybdenite which remained its surface hydrophobicity.

Tailoring the electrochemical properties of 2D-hBN via physical linear defects: physicochemical, computational and electrochemical characterisation.

Monolayer hexagonal-boron nitride films (2D-hBN) are typically reported within the literature to be electrochemically inactive due to their considerable band gap (ca. 5.2–5.8 eV). It is demonstrated herein that introducing physical linear defects (PLDs) upon the basal plane surface of 2D-hBN gives rise to electrochemically useful signatures. The reason for this transformation from insulator to semiconductor (inferred from physicochemical and computational characterisation) is likely due to full hydrogenation and oxygen passivation of the boron and/or nitrogen at edge sites. This results in a decrease in the band gap (from ca. 6.11 to 2.36/2.84 eV; theoretical calculated values, for the fully hydrogenated oxygen passivation at the N or B respectively). The 2D-hBN films are shown to be tailored through the introduction of PLDs, with the electrochemical behaviour dependent upon the surface coverage of edge plane-sites/defects, which is correlated with electrochemical performance towards redox probes (hexaammineruthenium(iii) chloride and Fe2+/3+) and the hydrogen evolution reaction. This manuscript de-convolutes, for the first time, the fundamental electron transfer properties of 2D-hBN, demonstrating that through implementation of PLDs, one can beneficially tailor the electrochemical properties of this nanomaterial.

Investigating the Integrity of Graphene towards the Electrochemical Hydrogen Evolution Reaction (HER)

Mono-, few-, and multilayer graphene is explored towards the electrochemical Hydrogen Evolution Reaction (HER). Careful physicochemical characterisation is undertaken during electrochemical perturbation revealing that the integrity of graphene is structurally compromised. Electrochemical perturbation, in the form of electrochemical potential scanning (linear sweep voltammetry), as induced when exploring the HER using monolayer graphene, creates defects upon the basal plane surface that increases the coverage of edge plane sites/defects resulting in an increase in the electrochemical reversibility of the HER process. This process of improved HER performance occurs up to a threshold, where substantial break-up of the basal sheet occurs, after which the electrochemical response decreases; this is due to the destruction of the sheet integrity and lack of electrical conductive pathways. Importantly, the severity of these changes is structurally dependent on the graphene variant utilised. This work indicates that multilayer graphene has more potential as an electrochemical platform for the HER, rather than that of mono- and few-layer graphene. There is huge potential for this knowledge to be usefully exploited within the energy sector and beyond.