Electrochemical Atomic Force Microscopy Research Articles

Recent development of samples’ surface properties using scanning ion conductance microscopy

Scanning ion conductance microscopy has a widespread application in imaging non-conductive substrates, especially biological samples due to its high-resolution and non-contact imaging. In this work, state-of-the-art achievements on exploring samples’ surface properties including surface morphology, sample conductivity and dynamics using scanning ion conductance microscopy are firstly introduced, which confirm that scanning ion conductance microscopy is such a mature technology that realises non-invasive and high-resolution imaging. Then, combinations with scanning electrochemical microscopy and atomic force microscopy are demonstrated, which realise the multifunction of scanning ion conductance microscopy. Furthermore, improvements that can help enhance the imaging rate are presented. Finally, the future direction of scanning ion conductance microscopy is discussed.

A probeless and label-free electrochemical immunosensor for cystatin C detection based on ferrocene functionalized-graphene platform

A novel electrochemical sensor with inherent redox activity mediated by ferrocene for Cystatin C (CysC), an early kidney failure biomarker, is described. The current response was mediated by graphene oxide-ferrocene nanofilm with redox-activity coming from electroactive species surface-confined. Anti-CysC antibodies were immobilized by their Fc portions on the drop-casting polyethyleneimine (PEI) film for improving the sensitivity and reproducibility. Stepwise modifications of the nanostructured surface were characterized by electrochemical techniques, FT-IR and AFM. FT-IR confirmed the formation of the Fc-GO nanocomposite and PEI deposition on the electrode surface. The AFM micrographs confirmed a nanometric film of Fc-GO and PEI. The sensor platform showed a response from 0.1 to 1000 ng/mL and lower limit of detection (LOD) of 0.03 ng/mL of CysC, with good accuracy, specificity and it was successfully applied for CysC detection. Advantages of this immunosensor include rapid testing with minimal steps by the simple use of an intrinsic redox probe, working in a reduction potential, which avoids potential interferences. This proposal attempts to circumvent amperometric detection limitations and provides a promising candidate for future point-of-care diagnostics without redox probe additional solutions for measurements.

Operando Study of Lithium Dendrite Growth on Graphite Andoe By EC-AFM

Lithium dendrite growth is one of the most challenging problems affecting safety performance of lithium ion batteries (LIBs). It causes low Columbic efficiency as well as safety hazards for LIBs. Understanding the evolution process of Li dendrite growth at nanoscale is critical for solving this problem. Herein, we report an in-situ electrochemical atomic force microscopy (EC-AFM) investigation of the initial Li deposition in EC and FEC-based electrolytes on graphite electrodes. Our results showed solid electrolyte interphase (SEI) formed from FEC-based electrolyte can suppress Li dendrite growth. FEC-based electrolyte induced formation of LiF-rich SEI films which were harder and denser than that formed in EC-based electrolyte. Combining with its better mechanical property and larger resistance, the SEI layer formed from FEC-based electrolyte is sufficient to slow down Li+ ions intercalation, prevent reduction of Li+ ions and Li deposition get electrons to deposit on the graphite surface. Our results demonstrated that EC-AFM is a powerful in-situ technique for the study of lithium dendrite growth.

Ir/TiC/Pt Vs. Pt-Ir/TiC in Role of Magnetron Sputtered Thin-Film Catalyst for Anode of PEM Reversible Fuel Cell

Ever increasing amount of installed power capacity from the volatile renewable sources (e.g. wind and solar) puts high demand on a reliable and scalable system, capable of storing the energy during the overproduction and releasing it in times of the deficit. Utilization of hydrogen as an energy vector proves to be an interesting option in this context. Overproduced electrical energy can be electrochemically converted to hydrogen by means of the water electrolyzers (WEs). Generated hydrogen can be either injected into the existing natural gas pipelines or stored for later conversion back to electricity via the fuel cells (FCs). The most suitable WEs and FCs for this task are arguably the proton exchange membrane WEs and FCs (PEM-WEs, PEM-FCs). Major factor currently hindering wider commercialization of these technologies is the high price and scarcity of noble metals, namely Pt and Ir which serve the role of a catalyst within the individual cells. One way of lowering the loading of noble metals is by using thin-film techniques for their deposition onto the high-surface conductive nanoparticles. Another approach, which is convenient in applications where the complete cycle of electricity->H2->electricity takes place, is merging the PEM-WEs and PEM-FCs into one bi-functional system – the PEM unitized reversible fuel cell (PEM-URFC). Such unification may potentially lead to significant cost savings not only on the catalyst but on the overall hardware as well. In this work, we present and discuss unorthodoxly prepared bi-functional thin-film low-loading Pt-Ir catalysts for the anode side of PEM-URFC (i.e. the oxygen evolution/hydrogen oxidation side). Two different geometries of the catalyst coated membranes (CCM) were studied; the CCM with magnetron co-sputtered Pt-Ir catalyst on top of the TiC-based support sublayer and the CCM with sandwich-like design where Pt is magnetron sputtered on the bottom and Ir on the top side of the TiC-based support sublayer. Although the loading of noble metals within both tested CCMs and the corresponding membrane electrode assemblies (MEAs) was similar, the obtained in-cell efficiency varied significantly. The sandwich-like CCM performed better in both electrolyzer and fuel cell regimes. Combination of data obtained from the in-cell performance measurements, X-ray photoelectron spectroscopy (XPS) and electrochemical atomic force microscopy (EC-AFM) helped us to identify the reasons why sandwich-like CCM performed better in both operational regimes. We concluded that thorough oxidation of Ir to IrO2, which did not occur when Ir was within Pt-Ir alloy after co-sputtering, was responsible for higher efficiency of the sandwich-like CCM in PEM-WE regime. On the other hand, the less prominent increase of efficiency in PEM-FC mode seemed to be due to the swapping of Pt thin film from position "top" (i.e. further from the PEM) to position "bottom" (i.e. closer to the PEM) which allowed for better ionic conductivity. Considering relatively high efficiencies obtained by the sandwich-like MEA with just a fraction of conventional noble metal loading, we believe that continuing in the research of thin-film, segmented catalysts is the step in the right direction.

High‐Rate, Tunable Syngas Production with Artificial Photosynthetic Cells

AbstractAn artificial photosynthetic (APS) system consisting of a photoanodic semiconductor that harvests solar photons to split H2O, a Ni‐SNG cathodic catalyst for the dark reaction of CO2 reduction in a CO2‐saturated NaHCO3 solution, and a proton‐conducting membrane enabled syngas production from CO2 and H2O with solar‐to‐syngas energy‐conversion efficiency of up to 13.6 %. The syngas CO/H2 ratio was tunable between 1:2 and 5:1. Integration of the APS system with photovoltaic cells led to an impressive overall quantum efficiency of 6.29 % for syngas production. The largest turnover frequency of 529.5 h−1 was recorded with a photoanodic N‐TiO2 nanorod array for highly stable CO production. The CO‐evolution rate reached a maximum of 154.9 mmol g−1 h−1 in the dark compartment of the APS cell. Scanning electrochemical–atomic force microscopy showed the localization of electrons on the single‐nickel‐atom sites of the Ni‐SNG catalyst, thus confirming that the multielectron reduction of CO2 to CO was kinetically favored.

High-Rate, Tunable Syngas Production with Artificial Photosynthetic Cells.

An artificial photosynthetic (APS) system consisting of a photoanodic semiconductor that harvests solar photons to split H2 O, a Ni-SNG cathodic catalyst for the dark reaction of CO2 reduction in a CO2 -saturated NaHCO3 solution, and a proton-conducting membrane enabled syngas production from CO2 and H2 O with solar-to-syngas energy-conversion efficiency of up to 13.6 %. The syngas CO/H2 ratio was tunable between 1:2 and 5:1. Integration of the APS system with photovoltaic cells led to an impressive overall quantum efficiency of 6.29 % for syngas production. The largest turnover frequency of 529.5 h-1 was recorded with a photoanodic N-TiO2 nanorod array for highly stable CO production. The CO-evolution rate reached a maximum of 154.9 mmol g-1 h-1 in the dark compartment of the APS cell. Scanning electrochemical-atomic force microscopy showed the localization of electrons on the single-nickel-atom sites of the Ni-SNG catalyst, thus confirming that the multielectron reduction of CO2 to CO was kinetically favored.

Elucidating the interfacial evolution and anisotropic dynamics on silicon anodes in lithium-ion batteries

Silicon (Si) has been considered as one of the most promising anodes in secondary high-energy rechargeable lithium-ion batteries (LIBs) owing to its high theoretical specific capacity and abundant reserves, whereas it suffers from an unstable solid electrolyte interphase (SEI) film and dramatic volume expansion. Herein, in situ electrochemical atomic force microscopy (AFM) and visual videos were used to reveal the interphasial properties of SEI film and anisotropic dynamics upon lithiation/delithiation processes on the single-crystalline Si electrodes with different crystal plane orientations. Lithiation of Si (111) prefer to grow along the <121> direction in the XY plane with the shape of oriented rods, in contrast, that of Si (100) form cone-like structure with the axial direction of <100> perpendicular to the (100) surface. Quantitative dynamic processes elucidate the preferable reversibility in Si (111) system, revealing the corresponding structure-reactivity correlations.

Atomic force microscopy study of nanoporous gold surface and electrochemical properties

The morphology, surface oxide and strain evolution of nanoporous (np) gold were investigated using atomic force microscopy (AFM). Topographic AFM images show typical np structure with a few nanometers ligament size. Current sensing AFM results revealed semiconductor properties of the surface oxide, which may consist of Ag2O (p-type) and AgO (n-type). The surface oxide can effectively suppress the np structure coarsening. In-situ electrochemical AFM tests exhibit a refined macroscopic dimensional change of 40 nm within 0.35–0.7 V potential range. AFM can be used as an effective method to investigate the morphology and voltage-induced dimension changes in electrolyte.

Hysteretic order-disorder transitions of ionic liquid double layer structure on graphite

Understanding the electrical double layer (EDL) structure at the solid/liquid interface is critical towards realizing the full potential of electrochemical applications using ionic liquids. In this work, the out-of-plane and in-plane EDL structures of PYR14-TFSI on graphite (HOPG) have been studied by in-situ electrochemical atomic force microscopy (AFM) and molecular dynamics (MD) simulation. AFM results revealed that the first adsorbed ion layer on HOPG consists of both disordered and ordered lateral domains. It has been found that the neighboring molecules in the x-y plane form intricate ordered lateral structures on length scale of hundreds of nanometers, and the out-of-plane EDL structure is independent of the in-plane structure. MD simulations under zero polarization showed that in the first adsorbed layer, cations have one preferred orientation while anions have two preferred orientations in relation to the HOPG surface, which might be the origin of the complex lateral ordering. When polarizing the surface, a hysteretic order-disorder transition of the lateral ordering in the first adsorbed layer can be observed by in-situ AFM, and the ordered domains disappear for high positive or negative voltages. Comparison with bias-dependent MD reveals that the existence of a bimodal anion distribution in the first absorbed layer can be linked to the observed transitions giving new insights into the origin of the structural domains, which can help understand unusual charge and discharge kinetics observed in similar systems.

Revealing the Surface Effect of the Soluble Catalyst on Oxygen Reduction/Evolution in Li-O2 Batteries.

Understanding catalytic mechanisms at the nanoscale is essential for the advancement of lithium-oxygen (Li-O2) batteries. Using in situ electrochemical atomic force microscopy, we explored the interfacial evolution during the Li-O2 electrochemical reactions in dimethyl sulfoxide-based electrolyte, further revealing the surface catalytic mechanism of the soluble catalyst 2,5-di- tert-butyl-1,4-benzoquinone (DBBQ). The real-time views showed that during discharge flower-like Li2O2 formed in the electrolyte with DBBQ but small toroid without DBBQ. Upon charge, Li2O2 decomposes at a slow rate from bottom to top in the absence of DBBQ, yet with an outside-in approach in the presence of DBBQ. Bigger discharge products and more efficient decomposition pathways in the DBBQ-containing system reveal the catalytic activity of DBBQ straightforwardly. Our work provides a direct insight into the surface effect of soluble catalyst DBBQ on Li-O2 reactions at the nanoscale, which is critical for the performance optimization of Li-O2 batteries.

Development of a New Electrochemical Atomic Force Microscopy Tool for Obtaining Surface Morphology Through Electrochemical Reaction.

Electrochemical atomic force microscopy is a complex electrochemical analysis method that has been applied in many fields. Electrochemical atomic force microscopy consists of an electrochemical cell, electrochemical analysis system, and atomic force microscopy. To simultaneously analyze the electrochemical system and the atomic force microscopy, an electrochemical cell with a suitable structure is needed. We developed the electrochemical atomic force microscopy analysis system using a self-developed electrochemical cell. To confirm the in-situ analytical ability of the developed electrochemical atomic force microscopy analysis system, we observed the electrochemical corrosion process of copper with respect to changes in pH of a sulfuric acid solution. The operation of the electrochemical atomic force microscopy tool was verified by experiments on the electrochemical corrosion of copper, and the factors affecting the corrosion process were examined. It was confirmed that electrochemical atomic force microscopy can perform electrochemical analysis and atomic force microscopy image analysis at the same time.

Effects of probe downforce and bias voltage on electrochemical atomic force microscopy nanomachining of copper materials

This study applied electrochemical atomic force microscopy in a liquid environment. Copper was used to conduct an experiment involving nanoscale electrochemically assisted machining. Experimental conditions (e.g., number of scans, bias voltage, and electrolyte formula) were adjusted to explore the resulting phenomena and effects on nanoscale electrochemically assisted machining. The experiments showed that increasing downforce in air did not significantly influence the Cu specimen. In 0.01M phosphoric acid, applying a small amount of downforce and bias voltage resulted in a significant machining outcome. Optimal machining efficiency was achieved in the presence of both 0.01M H3PO4 and bias voltage of 0.5 V. Moreover, after machining, a small amount of oxide was scraped off the Cu surface and adhered to the probe.

In Situ Nanoscale Redox Mapping Using Tip-Enhanced Raman Spectroscopy.

Electrochemical atomic force microscopy tip-enhanced Raman spectroscopy (EC-AFM-TERS) was used for the first time to spatially resolve local heterogeneity in redox behavior on an electrode surface in situ and at the nanoscale. A structurally well-defined Au(111) nanoplate located on a polycrystalline ITO substrate was studied to examine nanoscale redox contrast across the two electrode materials. By monitoring the TERS intensity of adsorbed Nile Blue (NB) molecules on the electrode surface, TERS maps were acquired with different applied potentials. The EC-TERS maps showed a spatial contrast in TERS intensity between Au and ITO. TERS line scans near the edge of a 20 nm-thick Au nanoplate demonstrated a spatial resolution of 81 nm under an applied potential of -0.1 V vs Ag/AgCl. The intensities from the TERS maps at various applied potentials followed Nernstian behavior, and a formal potential ( E0') map was constructed by fitting the TERS intensity at each pixel to the Nernst equation. Clear nanoscale spatial contrast between the Au and ITO regions was observed in the E0' map. In addition, statistical analysis of the E0' map identified a statistically significant 4 mV difference in E0' on Au vs ITO. Electrochemical heterogeneity was also evident in the E0' distribution, as a bimodal distribution was observed in E0' on polycrystalline ITO, but not on gold. A direct comparison between an AFM friction image and the E0' map resolved the electrochemical behavior of individual ITO grains with a spatial resolution of ∼40 nm. The variation in E0' was attributed to different local surface charges on the ITO grains. Such site-specific electrochemical information with nanoscale spatial and few mV voltage resolutions is not available using ensemble spectroelectrochemical methods. We expect that in situ redox mapping at the nanoscale using EC-AFM-TERS will have a crucial impact on understanding the role of nanoscale surface features in applications such as electrocatalysis.

A novel metal-organic layered material with superior supercapacitive performance through ultrafast and reversible tetraethylammonium intercalation

Supercapacitors can deliver high electrical power because of fast ion adsorption/desorption on the surface or surface redox reactions, which, in turn, restrict their energy density. To break surface-storage ceiling and further improve the energy density, here, we develop a cost-effective, layered material made of amorphous metal-organic nanosheets, Ni-p-phenylenediamine (Ni-pPD), with a large intersheet spacing of 1.6 nm for its robust and highly reversible intercalation reaction with tetraethylammonium cations. When coupled with activated carbon cathode, the 230 μm-thick Ni-pPD anode shows a high gravimetric capacitance (259 F g−1) and a high areal capacitance (2.9 F cm−2) at 2 A g−1 within a wide potential window of 2.85 V in the organic electrolyte of tetraethylammonium tetrafluoroborate/acetonitrile. In-situ electrochemical atomic force microscopy reveals that high kinetics at high potentials are attributed to the increased intersheet spacing under large polarization, demonstrating structural advantages of this novel material and its great potential for real-world applications.

Electrochemical assay for 20S proteasome activity and inhibition with anti-cancer drugs

The majority of eukaryotic regulated protein turnover is performed by the proteasome, a multi-catalytic enzyme. Due to the fact that proteasome enzyme abnormal functioning was observed in different malignant cells, the proteasome is becoming a target for medical treatment. In order to evaluate the mechanisms of action of pharmaceutical compounds on proteasome enzyme inhibition, detecting and characterizing its activity is essential. An electrochemical assay that allows the monitoring of the chymotrypsin-like activity and inhibition of the 20S proteasome enzyme, based on the electrochemical detection of an electroactive compound released upon proteolysis of an adequate chymotrypsin-substrate is described. By employing differential pulse voltammetric measurement, the activity of the 20S proteasome enzyme was investigated for different incubation times of 20S with oligopeptide substrate as well as for different concentrations of substrate. Enzyme kinetic parameters were determined by voltammetry and the electrochemical assay compared with fluorescence spectroscopy. Electrochemical quartz crystal microbalance and atomic force microscopy were also used to investigate substrate interaction with the 20S proteasome and their adsorption at the electrode surface. Finally, the new electrochemical assay allowed to investigate the mechanisms of two different proteasome inhibitor drugs, bortezomib and oprozomib, underlying the applicability of the assay for understanding proteasome inhibitor action.

Composites of Donor-π-Acceptor type configured organic compound and porous ZnO nano sheets as corrosion inhibitors of copper in chloride environment

Donor-π-Acceptor (D-π-A) type compounds are very interesting for corrosion study since they have unique structural configuration. Their high chemical reactivity promotes an easy bonding with the metals, which helps in corrosion inhibition. In this work, ethyl-2-cyano-3-(4-(dimethylamino) phenyl) acrylate (ECDPA) (a D-π-A type compound) is used to restrict the copper loss in 1 M HCl. The impedance analysis portrays that ECDPA saves 75% of copper at its maximum concentration in HCl solution. To further increase the inhibition efficiency, ECDPA-ZnO composites are developed. The ZnO is synthesized hydrothermally and calcined at two different temperatures (300 °C and 500 °C). The morphology of synthesized ZnO changes drastically with calcination; however, the main morphological difference in ZnO at 300 °C (Z3) and ZnO at 500 °C (Z5) is increment of porosity. Hence, two composites are made to analyze the change in corrosion behavior of the composites. The composites are designated as: ECDPA-ZnO at 300 °C to EZ3 and ECDPA-ZnO at 500 °C to EZ5. The characterizations of ZnO, ECDPA and ECDPA-ZnO composites have been performed by UV–visible spectroscopy, FTIR spectroscopy, HRTEM, HRSEM, EDAX and XRD techniques. The corrosion inhibition efficiencies of EZ3 and EZ5 are achieved as 78% and 81%. This fact suggests that ZnO increases the adsorption of ECDPA over copper surface, which is confirmed by Langmuir adsorption analysis and electrochemical atomic force microscopy (EC-AFM) measurements.

Electrochemical DNA Sensors with Layered Polyaniline-DNA Coating for Detection of Specific DNA Interactions.

A DNA sensor has been proposed on the platform of glassy carbon electrode modified with native DNA implemented between two electropolymerized layers of polyaniline. The surface layer was assembled by consecutive stages of potentiodynamic electrolysis, DNA drop casting, and second electrolysis, which was required for capsulation of the DNA molecules and prevented their leaching into the solution. Surface layer assembling was controlled by cyclic voltammetry, electrochemical impedance spectroscopy, atomic force, and scanning electron microscopy. For doxorubicin measurement, the DNA sensor was first incubated in the Methylene blue solution that amplified signal due to DNA intercalation and competition with the doxorubicin molecules for the DNA binding sites. The charge transfer resistance of the inner layer interface decreased with the doxorubicin concentration in the range from 1.0 pM to 0.1 μM (LOD 0.6 pM). The DNA sensor was tested for the analysis of spiked artificial urine samples and showed satisfactory recovery in concentration range of 0.05–10 μM. The DNA sensor developed can find application in testing of antitumor drugs and some other DNA damaging factors.

Atomic Force Microscopy Meets Biophysics, Bioengineering, Chemistry, and Materials Science.

Briefly, herein the use of atomic force microscopy (AFM) in the characterization of molecules and (bioengineered) materials related to chemistry, materials science, chemical engineering, and environmental science and biotechnology is reviewed. First, the basic operations of standard AFM, Kelvin probe force microscopy, electrochemical AFM, and tip‐enhanced Raman microscopy are described. Second, several applications of these techniques to the characterization of single molecules, polymers, biological membranes, films, cells, hydrogels, catalytic processes, and semiconductors are provided and discussed.

The Origin of Electrochemical Actuation of MnO2/Ni Bilayer Film Derived by Redox Pseudocapacitive Process

AbstractPseudocapacitance‐induced electrochemical actuators (EC‐actuators) have attracted great attention in robots and artificial intelligence technologies. Despite major efforts to design such EC‐actuators, a molecular‐level understanding of the deformation mechanism is still lacking. Here, a reversible deformation of a freestanding MnO2/Ni bilayer film is demonstrated and in situ electrochemical atomic force microscopy, in situ Raman spectroscopy, and density functional theory simulation are used to study the origin of the deformation. The results show that the electrochemical actuation of the MnO2/Ni film is highly related with the redox pseudocapacitive behavior of MnO2 layer. Valence state variation of Mn element, shortening and lengthening of MnO bond, and insertion and extraction of Na+ ions, which all result from the redox pseudocapacitance of MnO2 during charging and discharging, eventually lead to the reversible contraction and expansion of MnO2 morphology. Such action counters with the nonactive Ni layer, finally inducing the reversible deformation of the MnO2/Ni bilayer film. It is believed that the study can provide useful guidance to design better EC‐actuators in the future.

Cu2S nanocrystals incorporated highly efficient non-fullerene ternary organic solar cells

Here, we report Cu2S nanocrystals based non-fullerene ternary polymer solar cells by incorporating Cu2S in conjugated polymer (PBDB-T: poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl) benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))]) and small molecule non-fullerene compound (ITIC:3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene). The devices were fabricated in inverted configuration i.e. ITO/ZnO/PBDB-T: Cu2S NCs: ITIC/MoO3/Ag. Effect of concentration of Cu2S nanocrystals on the performance parameters of PBDB-T: ITIC based organic solar cells is studied. An enhancement in the power conversion efficiency from 8.24% to 9.53% is achieved for the optimum concentration of Cu2S nanocrystals in the organic photoactive blend. The cause of improvement in the performance parameters of the device is investigated by means of the light intensity dependent electrochemical impedance spectroscopy and atomic force microscopy. It is found that the devices with Cu2S nanocrystals have less trap-assisted recombination.