In Situ Electropolymerizing Toward EP-CoP/Cu Tandem Catalyst for Enhanced Electrochemical CO2-to-Ethylene Conversion.

Electrochemical CO2 reduction has garnered significant interest in the conversion of sustainable energy to valuable fuels and chemicals. Cu-based bimetallic catalysts play a crucial role in enhancing *CO concentration on Cu sites for efficient C─C coupling reactions, particularly for C2 product generation. To enhance Cu's electronic structure and direct its selectivity toward C2 products, a novel strategy is proposed involving the in situ electropolymerization of a nano-thickness cobalt porphyrin polymeric network (EP-CoP) onto a copper electrode, resulting in the creation of a highly effective EP-CoP/Cu tandem catalyst. The even distribution of EP-CoP facilitates the initial reduction of CO2 to *CO intermediates, which then transition to Cu sites for efficient C─C coupling. DFT calculations confirm that the *CO enrichment from Co sites boosts *CO coverage on Cu sites, promoting C─C coupling for C2+ product formation. The EP-CoP/Cu gas diffusion electrode achieves an impressive current density of 726 mA cm-2 at -0.9 V versus reversible hydrogen electrode (RHE), with a 76.8% Faraday efficiency for total C2+ conversion and 43% for ethylene, demonstrating exceptional long-term stability in flow cells. These findings mark a significant step forward in developing a tandem catalyst system for the effective electrochemical production of ethylene.

Scanning Electrochemical Probe Lithography for Ultra-Precision Machining of Micro-Optical Elements with Freeform Curved Surface.

Two challenges should be overcome for the ultra-precision machining of micro-optical element with freeform curved surface: one is the intricate geometry, the other is the hard-to-machining optical materials due to their hardness, brittleness or flexibility. Here scanning electrochemical probe lithography (SECPL) is developed, not only to meet the machining need of intricate geometry by 3D direct writing, but also to overcome the above mentioned mechanical properties by an electrochemical material removal mode. Through the electrochemical probe a localized anodic voltage is applied to drive the localized corrosion of GaAs. The material removal rate is obtained as a function of applied voltage, motion rate, scan segment, etc. Based on the material removal function, an arbitrary geometry can be converted to a spatially distributed voltage. Thus, a series of micro-optical element are fabricated with a machining accuracy in the scale of 100 s of nanometers. Notably, the spiral phase plate shows an excellent performance to transfer parallel light to vortex beam. SECPL demonstrates its excellent controllability and accuracy for the ultra-precision machining of micro-optical devices with freeform curved surface, providing an alternative chemical approach besides the physical and mechanical techniques.

Salt gradient enhanced sensitivity in nanopores for intracellular calcium ion detection.

Intracellular calcium ion detection is of great significance for understanding the cell metabolism and signaling pathways. Most of the current ionic sensors either face the size issue or sensitivity limit for the intracellular solution with high background ion concentrations. In this paper, we proposed a calmodulin (CaM) functionalized nanopore for sensitive and selective Ca2+ detection inside living cells. A salt gradient was created when the nanopore sensor filled with a low concentration electrolyte was in contact with a high background concentration solution, which enhanced the surface charge-based detection sensitivity. The nanopore sensor showed a 10 × sensitivity enhancement by application of a 100-fold salt gradient, and a detection limit of sub nM. The sensor had a wide detection range from 1 nM to 1 mM, and allowed for quick calcium ion quantification in a few seconds. The sensor was demonstrated for intracellular Ca2+ detection in A549 cells in response to ionomycin.

Regulation of heterogeneous electron transfer reactivity by defect engineering through electrochemically induced brominating addition.

Enhancing the electrochemical activity of graphene holds great significance for expanding its applications in various electrochemistry fields. In this study, we have demonstrated a facile and quantitative approach for modulating the defect density of single-layer graphene (SLG) via an electrochemically induced bromination process facilitated by cyclic voltammetry. This controlled defect engineering directly impacts the heterogeneous electron transfer (HET) rate of SLG. By utilizing Raman spectroscopy and scanning electrochemical microscopy (SECM), we have established a correlation between the HET kinetics and both the defect density (nD) and mean distance between defects (LD) of SLG. The variation of the HET rate (k0) with the defect density manifested a distinctive three-stage behavior. Initially, k0 increased slightly with the increasing nD, and then it experienced a rapid increase as nD further increased. However, once the defect density surpassed a critical value of about 1.8 × 1012 cm-2 (LD < 4.2 nm), k0 decreased rapidly. Notably, the results revealed a remarkable 35-fold enhancement of k0 under the optimal defect density conditions compared to pristine SLG. This research paves the way for controllable defect engineering as a powerful strategy to enhance the electrochemical activity of graphene, opening up new possibilities for its utilization in a wide range of electrochemical applications.

Ultrasonic-Assisted Electrochemical Nanoimprint Lithography: Forcing Mass Transfer to Enhance the Localized Etching Rate of GaAs.

Electrochemical nanoimprint lithography (ECNL) has emerged as a promising technique for fabricating three-dimensional micro/nano-structures (3D-MNSs) directly on semiconductor wafers. This technique is based on a localized corrosion reaction induced by the contact potential across the metal/semiconductor boundaries. The anodic etching of semiconductor and the cathodic reduction of electron acceptors occur at the metal/semiconductor/electrolyte interface and the Pt mold surface, respectively. However, the etching rate is limited by the mass transfer of species in the ultrathin electrolyte layer between the mold and the workpiece. To overcome this challenge, we introduce the ultrasonics effect into the ECNL process to facilitate the mass exchange between the ultrathin electrolyte layer and the bulk solution, thereby improving the imprinting efficiency. Experimental investigations demonstrate a positive linear relationship between the reciprocal of the area duty ratio of the mold and the imprinting efficiency. Furthermore, the introduction of ultrasonics improves the imprinting efficiency by approximately 80 %, irrespective of the area duty ratio. The enhanced imprinting efficiency enables the fabrication of 3D-MNSs with higher aspect ratios, resulting in a stronger light trapping effect. These results indicate the prospective applications of ECNL in semiconductor functional devices, such as photoelectric detection and photovoltaics.

In situ Electropolymerized 3D Microporous Cobalt-Porphyrin Nanofilm for Highly Effective Molecular Electrocatalytic Reduction of Carbon Dioxide.

Electrocatalytic CO2 reduction reaction (CO2 RR) based on molecular catalysts, for example, cobalt porphyrin, is promising to enhance the carbon cycle and mitigate current climate crisis. However, the electrocatalytic performance and accurate evaluations remain problems because of either the low loading amount or the low utilization rate of the electroactive CoN4 sites. Herein a monomer is synthesized, cobalt(II)-5,10,15,20-tetrakis(3,5-di(thiophen-2-yl)phenyl)porphyrin (CoP), electropolymerized onto carbon nanotubes (CNTs) networks, affording a molecular electrocatalyst of 3D microporous nanofilm (EP-CoP, 2-3 nm thickness) with highly dispersed CoN4 sites. The new electrocatalyst shortens the electron transfer pathway, accelerates the redox kinetics of CoN4 sites, and improves the durability of the electrocatalytic CO2 RR. From the intrinsic redox behavior of CoN4 sites, the effective utilization rate is obtained as 13.1%, much higher than that of the monomer assembled electrode (5.8%), and the durability is also promoted dramatically (>40 h) in H-type cells. In commercial flow cells, EP-CoP can achieve a faradic efficiency for CO (FECO ) over 92% at an overpotential of 160 mV. At a higher overpotential of 620 mV, the working current density can reach 310 mA cm-2 with a high FECO of 98.6%, representing the best performance for electrodeposited molecular porphyrin electrocatalysts.

Electrochemical regulation of the band gap of single layer graphene: from semimetal to semiconductor.

As a semimetal with a zero band gap and single-atom-scale thickness, single layer graphene (SLG) has excellent electron conductivity on its basal plane. If the band gap could be opened and regulated controllably, SLG would behave as a semiconductor. That means electronic elements or even electronic circuits with single-atom thickness could be expected to be printed on a wafer-scale SLG substrate, which would bring about a revolution in Moore's law of integrated circuits, not by decreasing the feature size of line width, but by piling up the atomic-scale-thickness of an SLG circuit board layer by layer. Employing scanning electrochemical microscopy (SECM), we have demonstrated that the electrochemically induced brominating addition reaction can open and regulate the band gap of SLG by forming SLG bromide (SLGBr). The SLG/SLGBr/SLG Schottky junction shows excellent performance in current rectification, and the rectification potential region can be regulated by tuning the degree of bromination of SLG. This work provides a feasible and effective way to regulate the band gap of SLG, which would open new applications for SLG in micro-nano electronics and ultra-large-scale integrated circuits (ULSI).

Dynamically Interfacial pH-Buffering Effect Enabled by N-Methylimidazole Molecules as Spontaneous Proton Pumps toward Highly Reversible Zinc-Metal Anodes.

Aqueous zinc-metal batteries have attracted extensive attention due to their outstanding merits of high safety and low cost. However, the intrinsic thermodynamic instability of zinc in aqueous electrolyte inevitably results in hydrogen evolution, and the consequent generation of OH- at the interface will dramatically exacerbate the formation of dead zinc and dendrites. Herein, a dynamically interfacial pH-buffering strategy implemented by N-methylimidazole (NMI) additive is proposed to remove the detrimental OH- at zinc/electrolyte interface in real-time, thus eliminating the accumulation of by-products fundamentally. Electrochemical quartz crystal microbalance and molecular dynamics simulation results reveal the existence of an interfacial absorption layer assembled by NMI and protonated NMI (NMIH+ ), which acts as an ion pump for replenishing the interface with protons constantly. Moreover, an in situ interfacial pH detection method with micro-sized spatial resolution based on the ultra-microelectrode technology is developed to probe the pH evolution in diffusion layer, confirming the stabilized interfacial chemical environment in NMI-containing electrolyte. Accordingly, with the existence of NMI, an excellent cumulative plating capacity of 4.2 Ah cm-2 and ultrahigh Coulombic efficiency of 99.74% are realized for zinc electrodes. Meanwhile, the NMI/NMIH+ buffer additive can accelerate the dissolution/deposition process of MnO2 /Mn2+ on the cathode, leading to enhanced cycling capacity.

Electrochemical Storage of Atomic Hydrogen on Single Layer Graphene.

If hydrogen can be stored and carried safely at a high density, hydrogen-fuel cells offer effective solutions for vehicles. The stable chemisorption of atomic hydrogen on single layer graphene (SLG) seems a perfect solution in this regard, with a theoretical maximum storage capacity of 7.7 wt %. However, generating hydrogenated graphene from H2 requires extreme temperatures and pressures. Alternatively, hydrogen adatoms can easily be produced under mild conditions by the electroreduction of protons in solid/liquid systems. Graphene is electrochemically inert for this reaction, but H-chemisorption on SLG can be carried out under mild conditions via a novel Pt-electrocatalyzed "spillover-surface diffusion-chemisorption" mechanism, as we demonstrate using dynamic electrochemistry and isotopic Raman spectroscopy. The apparent surface diffusion coefficient (∼10-5 cm2 s-1), capacity (∼6.6 wt %, ∼85.7% surface coverage), and stability of hydrogen adatoms on SLG at room temperature and atmospheric pressure are significant, and they are perfectly suited for applications involving stored hydrogen atoms on graphene.

Direct Nanomachining on Semiconductor Wafer By Scanning Electrochemical Microscopy.

Scanning electrochemical microscopy (SECM) is one of the most important instrumental methods of modern electrochemistry due to its high spatial and temporal resolution. We introduced SECM into nanomachining by feeding the electrochemical modulations of the tip electrode back to the positioning system, and we demonstrated that SECM is a versatile nanomachining technique on semiconductor wafers using electrochemically induced chemical etching. The removal profile was correlated to the applied tip current when the tip was held stationary and when it was moving slowly (<20 µm s-1 ), and it followed Faraday's law. Both regular and irregular nanopatterns were translated into a spatially distributed current by the homemade digitally controlled SECM instrument. The desired nanopatterns were "sculpted" directly on a semiconductor wafer by SECM direct-writing mode. The machining accuracy was controlled to the sub-micrometer and even nanometer scales. This advance is expected to play an important role in electrochemical nanomachining for 3D micro/nanostructures in the semiconductor industry.

Photosynergetic Electrochemical Synthesis of Graphene Oxide.

Here we propose a strategy of radical oxidation reaction for the high-efficiency production of graphene oxide (GO). GO plays important roles in the sustainable development of energy and the environment, taking advantages of oxygen-containing functional groups for good dispersibility and assembly. Compared with Hummers' method, electrochemical exfoliation of graphite is considered facile and green, although the oxidation is fairly low. To synthesize GO with better crystallinity and higher oxidation degree, we present a photosynergetic electrochemical method. By using oxalate anions as the intercalation ions and co-reactant, the interfacial concentration of hydroxyl radicals generated during electrochemical exfoliation was promoted, and the oxidation degree was comparable with that of GO prepared by Hummers' method. In addition, the crystallinity was improved with fewer layers and larger size. Moreover, the aniline coassembled GO membrane was selectively permeable to water molecules by the hydrogen-bond interaction, but it was impermeable to Na+, K+, and Mg2+, due to the electrostatic interactions. Thus, it has a prospective application to water desalination and purification. This work opens a novel approach to the direct functionalization of graphene during the electroexfoliation processes and to the subsequent assembly of the functionalized graphene.

Photoelectric effect accelerated electrochemical corrosion and nanoimprint processes on gallium arsenide wafers.

Here we report photoelectric-effect-enhanced interfacial charge transfer reactions. The electrochemical corrosion rate of n-type gallium arsenide (n-GaAs) induced by the contact potential at platinum (Pt) and GaAs boundaries can be accelerated by the photoelectric effect of n-GaAs. When a GaAs wafer is illuminated with a xenon light source, the electrons in the valence band of GaAs will be excited to the conduction band and then move to the Pt boundaries due to the different work functions of the two materials. This results in an enhanced contact electric field as well as an enlarged Pt/GaAs contact potential. Consequently, in the presence of electrolyte solution, the polarizations of both the Pt/solution interface and the GaAs/solution interface at the Pt/GaAs/solution 3-phase boundary are enhanced. If the accumulated electrons on the Pt side are removed by electron acceptors in the solution, anodic corrosion of GaAs will be accelerated strictly along the Pt/GaAs/solution 3-phase boundary. This photo-enhanced electrochemical phenomenon can increase the corrosion rate of GaAs and accelerate the process of electrochemical nanoimprint lithography (ECNL) on GaAs. The method opens an innovative, highly efficient, low-cost nanoimprint technique performed directly on semiconductors, and it has prospective applications in the semiconductor industry.

Three-dimensional paper based platform for automatically running multiple assays in a single step.

Paper based assays are paving the way to automated, simplified, robust and cost-effective point of care testing (POCT). We propose a method for fabricating three dimensional (3D) microfluidic paper based analytical devices (µPADs) via combining thin adhesive films and paper folding, which avoids the use of cellulose powders and the complex folding sequence and simultaneously permits assays in several layers. To demonstrate the effectiveness of this approach, a 3DµPADs was designed to conduct more assays on a small footprint, allowing dual colorimetric and electrochemical detections. More importantly, we further developed a 3D platform for implementing automated and multiplexed ELISA in parallel, since ELISA, a routine and standard laboratory method, has rarely been used in practical analyses outside of the laboratory. In this configuration, complex and multistep diagnostic assays can be carried out with the addition of the sample and buffer in a simple fashion. Using Troponin I as model, the device showed a broad dynamic range of detection with a detection limit of 0.35 ng/mL. Thus, the developed platforms allow for various assays to be cost-effectively carried out on a single 3D device, showing great potential in an academic setting and point of care testing under resource-poor conditions.

Electrochemical nanoimprint lithography: when nanoimprint lithography meets metal assisted chemical etching.

The functional three dimensional micro-nanostructures (3D-MNS) play crucial roles in integrated and miniaturized systems because of the excellent physical, mechanical, electric and optical properties. Nanoimprint lithography (NIL) has been versatile in the fabrication of 3D-MNS by pressing thermoplastic and photocuring resists into the imprint mold. However, direct nanoimprint on the semiconductor wafer still remains a great challenge. On the other hand, considered as a competitive fabrication method for erect high-aspect 3D-MNS, metal assisted chemical etching (MacEtch) can remove the semiconductor by spontaneous corrosion reaction at the metal/semiconductor/electrolyte 3-phase interface. Moreover, it was difficult for MacEtch to fabricate multilevel or continuously curved 3D-MNS. The question of the consequences of NIL meeting the MacEtch is yet to be answered. By employing a platinum (Pt) metalized imprint mode, we demonstrated that using electrochemical nanoimprint lithography (ECNL) it was possible to fabricate not only erect 3D-MNS, but also complex 3D-MNS with multilevel stages with continuously curved surface profiles on a gallium arsenide (GaAs) wafer. A concave microlens array with an average diameter of 58.4 µm and height of 1.5 µm was obtained on a ∼1 cm2-area GaAs wafer. An 8-phase microlens array was fabricated with a minimum stage of 57 nm and machining accuracy of 2 nm, presenting an excellent optical diffraction property. Inheriting all the advantages of both NIL and MacEtch, ECNL has prospective applications in the micro/nano-fabrications of semiconductors.

Contact electrification induced interfacial reactions and direct electrochemical nanoimprint lithography in n-type gallium arsenate wafer.

Although metal assisted chemical etching (MacEtch) has emerged as a versatile micro-nanofabrication method for semiconductors, the chemical mechanism remains ambiguous in terms of both thermodynamics and kinetics. Here we demonstrate an innovative phenomenon, i.e., the contact electrification between platinum (Pt) and an n-type gallium arsenide (100) wafer (n-GaAs) can induce interfacial redox reactions. Because of their different work functions, when the Pt electrode comes into contact with n-GaAs, electrons will move from n-GaAs to Pt and form a contact electric field at the Pt/n-GaAs junction until their electron Fermi levels (EF) become equal. In the presence of an electrolyte, the potential of the Pt/electrolyte interface will shift due to the contact electricity and induce the spontaneous reduction of MnO4- anions on the Pt surface. Because the equilibrium of contact electrification is disturbed, electrons will transfer from n-GaAs to Pt through the tunneling effect. Thus, the accumulated positive holes at the n-GaAs/electrolyte interface make n-GaAs dissolve anodically along the Pt/n-GaAs/electrolyte 3-phase interface. Based on this principle, we developed a direct electrochemical nanoimprint lithography method applicable to crystalline semiconductors.

Electrochemical micro/nano-machining: principles and practices.

Micro/nano-machining (MNM) is becoming the cutting-edge of high-tech manufacturing because of the increasing industrial demand for supersmooth surfaces and functional three-dimensional micro/nano-structures (3D-MNS) in ultra-large scale integrated circuits, microelectromechanical systems, miniaturized total analysis systems, precision optics, and so on. Taking advantage of no tool wear, no surface stress, environmental friendliness, simple operation, and low cost, electrochemical micro/nano-machining (EC-MNM) has an irreplaceable role in MNM. This comprehensive review presents the state-of-art of EC-MNM techniques for direct writing, surface planarization and polishing, and 3D-MNS fabrications. The key point of EC-MNM is to confine electrochemical reactions at the micro/nano-meter scale. This review will bring together various solutions to "confined reaction" ranging from electrochemical principles through technical characteristics to relevant applications.

Single molecular catalysis of a redox enzyme on nanoelectrodes.

Due to a high turnover coefficient, redox enzymes can serve as current amplifiers which make it possible to explore their catalytic mechanism by electrochemistry at the level of single molecules. On modified nanoelectrodes, the voltammetric behavior of a horseradish peroxidase (HRP) catalyzed hydroperoxide reduction no longer presents a continuous current response, but a staircase current response. Furthermore, single catalytic incidents were captured through a collision mode at a constant potential, from which the turnover number of HRP can be figured out statistically. In addition, the catalytic behavior is dynamic which may be caused by the orientation status of HRP on the surface of the electrode. This modified nanoelectrode methodology provides an electrochemical approach to investigate the single-molecule catalysis of redox enzymes.

Confined Chemical Etching for Electrochemical Machining with Nanoscale Accuracy.

In the past several decades, electrochemical machining (ECM) has enjoyed the reputation of a powerful technique in the manufacturing industry. Conventional ECM methods can be classified as electrolytic machining and electroforming: the former is based on anodic dissolution and the latter is based on cathodic deposition of metallic materials. Strikingly, ECM possesses several advantages over mechanical machining, such as high removal rate, the capability of making complex three-dimensional structures, and the practicability for difficult-to-cut materials. Additionally, ECM avoids tool wear and thermal or mechanical stress on machining surfaces. Thus, ECM is widely used for various industrial applications in the fields of aerospace, automobiles, electronics, etc. Nowadays, miniaturization and integration of functional components are becoming significant in ultralarge scale integration (ULSI) circuits, microelectromechanical systems (MEMS), and miniaturized total analysis systems (µ-TAS). As predicted by Moore's law, the feature size of interconnectors in ULSI circuits are down to several nanometers. In this Account, we present our perseverant research in the last two decades on how to "confine" the ECM processes to occur at micrometer or even nanometer scale, that is, to ensure ECM with nanoscale accuracy. We have been developing the confined etchant layer technique (CELT) to fabricate three-dimensional micro- and nanostructures (3D-MNS) on different metals and semiconductor materials since 1992. In general, there are three procedures in CELT: (1) generating the etchant on the surface of the tool electrode by electrochemical or photoelectrochemical reactions; (2) confining the etchant in a depleted layer with a thickness of micro- or nanometer scale; (3) feeding the tool electrode to etch the workpiece. Scavengers, which can react with the etchant, are usually adopted to form a confined etchant layer. Through the subsequent homogeneous reaction between the scavenger and the photo- or electrogenerated etchant in the electrolyte solution, the diffusion distance of the etchant is confined to micro- or nanometer scale, which ensures the nanoscale accuracy of electrochemical machining. To focus on the "confinement" of chemical etching reactions, external physical-field modulations have recently been introduced into CELT by introducing various factors such as light field, force field, hydrodynamics, and so on. Meanwhile, kinetic investigations of the confined chemical etching (CCE) systems are established based on the finite element analysis and simulations. Based on the obtained kinetic parameters, the machining accuracy is tunable and well controlled. CELT is now applicable for 1D milling, 2D polishing, and 3D microfabrication with an accuracy at nanometer scale. CELT not only inherits all the advantages of electrochemical machining but also provides advantages over photolithography and nanoimprint for its applicability to different functional materials without involving any photocuring and thermoplastic resists. Although there are some technical problems, for example, mass transfer and balance, which need to be solved, CELT has shown its prospective competitiveness in electrochemical micromachining, especially in the semiconductor industry.

Electrochemical buckling microfabrication.

Can isotropic wet chemical etching be controlled with a spatial resolution at the nanometer scale, especially, for the repetitive microfabrication of hierarchical 3D µ-nanostructures on the continuously curved surface of functional materials? We present an innovative wet chemical etching method called "electrochemical buckling microfabrication": first, a constant contact force is applied to generate a hierarchical 3D µ-nanostructure on a mold electrode surface through a buckling effect; then, the etchant is electrogenerated on-site and confined close to the mold electrode surface; finally, the buckled hierarchical 3D µ-nanostructures are transferred onto the surface of a Ga x In1-x P coated GaAs wafer through WCE. The concave microlens, with a Fresnel structure, has an enhanced photoluminescence at 630 nm. Comparing with energy beam direct writing techniques and nanoimprint lithography, this method provides an electrochemical microfabrication pathway for the semiconductor industry, with low cost and high throughput.

Synergetic effect enhanced photoelectrocatalysis.

We report synergetic effect enhanced photoelectrocatalysis, in which Fe(3+) and Br(-) are used as the acceptors of photogenerated charges on TiO2 nanoparticles. The kinetic rate of interfacial charge transfer is promoted from (4.0 ± 0.5) × 10(-4) cm s(-1) (TiO2/(O2, Br(-))) to (1.5 ± 0.5) × 10(-3) cm s(-1) (TiO2/(Fe(3+), Br(-))). The synergetic effect provides a valuable approach to the design of photoelectrocatalytic systems.