Noble Metal Electrodes Research Articles

Highly Effective 2D Layer Structured Titanium Carbide Electrode for Dye‐Sensitized and Perovskite Solar Cells

AbstractIn this study, 2D layer‐structured Ti3C2 is synthesized by using an etching method at lower temperature, which is then applied in dye‐sensitized and perovskite solar cells as counter electrode with higher activity compared with conventional TiC particles counter electrode. The dye‐sensitized solar cells fabricated by using a 2D layer‐structured Ti3C2 counter electrode achieves a power conversion efficiency of 9.57 %, much higher than that of the counterpart device fabricated using a TiC particle counter electrode (7.37 %). The excellent activity of the Ti3C2 electrode can be attributed to the superior charge transfer and mass transport properties, owing to the specific 2D layer structure. Moreover, the fabricated 2D layer‐structured Ti3C2 is applied in perovskite solar cells, thereby achieving a power conversion efficiency of 7.78 % without further optimization. Thus, it is a potential candidate for noble metal electrodes.

Heterogenized Pyridine-Substituted Cobalt(II) Phthalocyanine Yields Reduction of CO2 by Tuning the Electron Affinity of the Co Center.

Conversion of CO2 to reduced products is a promising route to alleviate irreversible climate change. Here we report the synthesis of a Co-based phthalocyanine with pyridine moieties (CoPc-Pyr), which is supported on a carbon electrode and shows Faradaic efficiency ∼90% for CO at 490 mV of overpotential (-0.6 V vs reversible hydrogen electrode (RHE)). In addition, its catalytic activity at -0.7 V versus RHE surpasses other Co-based molecular and metal-organic framework catalysts for CO2 reduction at this bias. Density functional theory calculations show that pyridine moieties enhance CO2 adsorption and electron affinity of the Co center by an inductive effect, thus lowering the overpotential necessary for CO2 conversion. Our study shows that CoPc-Pyr reduces CO2 at lower overpotential and with higher activity than noble metal electrodes, such as silver.

Toward High-Performance Electron/Hole-Transporting-Layer-Free, Self-Powered CsPbIBr2 Photodetectors via Interfacial Engineering.

Self-powered photodetectors (PDs) with inorganic lead halide perovskites hold multiple traits of high sensitivity, fast response, independence from external power supply, and excellent sustainability and stability, thus holding a great promise for practical applications. However, they generally contain high-temperature-processed electron-transporting layers (ETLs) and high-cost, unstable hole-transporting layers (HTLs) coupled with noble metal electrodes, which bring significant obstacles of production cost and stability for their potential commercialization. Herein, we demonstrate the building of high-performance HTL/ETL-free, self-powered CsPbIBr2 PD with simplified architecture of fluorine-doped tin oxide (FTO)/CsPbIBr2/carbon upon interfacial modification by polyethyleneimine (PEI). The optimized PD yields a dark current of 2.03 × 10-9 A, peak responsivity (R) of 0.32 A/W, maximum specific detectivity (D*) of 3.74 × 1012 Jones, and response time of 1.21 μs. These figures of merit are far beyond those of the one prepared without PEI modification and even the PD containing TiO2 ETL. Hence, our work suggests a highly feasible route to develop self-powered PDs with significantly simplified fabrication and a reduced production cost.

Nitrogen doping and titanium vacancies synergistically promote CO2 fixation in seawater.

The electrocatalytic generation of useful chemicals from CO2, H2O, and sustainable energy resources offers a promising strategy for the carbon cycle. However, the current CO2 electrolysis system is mainly operated in artificial electrolytes (e.g. ionic liquids and inorganic salt solutions), of which the high cost and impractical working conditions hinder its large-scale development. In this case, seawater represents an attractive alternative due to its abundance and good conductivity. Herein, we show that N-doping and titanium vacancies (VTi) can be introduced in Ti3C2 MXene nanosheets via a facile NH3-etching pyrolysis approach. These nanosheets demonstrate impressive CO2 reduction reaction (CO2RR) performances in seawater with a remarkable 92% faradaic efficiency and a partial current density of -16.2 mA cm-2 for CO production, being close to those of noble metal electrodes. Mechanistic studies reveal that the existence of N dopants and VTi synergistically modulates the electronic structure of the active Ti site, on which the free energy barriers for the key *COOH formation and desorption of *CO are greatly reduced, thereby leading to a notable CO2RR improvement. This study provides an opportunity for developing an active and cost-effective CO2 electrolysis system by using seawater as the electrolyte.

New life for old wires: electrochemical sensor method for neural implants

Objective. Electrochemical microsensors based on noble metals can give essential information on their microenvironment with high spatio-temporal resolution. However, most advanced chemo- and biosensors lack the long-term stability for physiological monitoring of brain tissue beyond an acute application. Noble metal electrodes are widely used as neural interfaces, particularly for stimulating in the central nervous system. Our goal was to recruit already deployed, unmodified noble metal electrodes (Pt, Pt/Ir) as in situ chemical sensors. Approach. With advanced electrochemical sensor methods, we investigated electrode surface processes, oxidizable species and oxygen as an indicator for tissue mass transport. We developed a unique, multi-step, amperometric/potentiometric sensing procedure derived from the investigation of Pt surface processes by chronocoulometry providing fundamental characterization of the electrode itself. Main results. The resulting electrochemical protocol preconditions the electrode, measures oxidizable and reducible species, and the open circuit potential (OCP). A linear, stable sensor performance was demonstrated, also in the presence of proteins, validating signal stability of our cyclic protocol in complex environments. We investigated our sensor protocol with microelectrodes on custom Pt/Ir-wire tetrodes by in vivo measurements in the rat brain for up to four weeks. Results showed that catalytic activity of the electrode is lost over time, but our protocol is repeatedly able to both quantify and restore electrode sensitivity in vivo. Significance. Our approach is highly relevant because it can be applied to any existing Pt electrode. Current methods to assess the brain/electrode microenvironment mainly rely on imaging techniques, histology and analysis of explanted devices, which are often end-point methods. Our procedure delivers online and time-transient information on the chemical microenvironment directly at the electrode/tissue interface of neural implants, gives new insight into the charge transfer processes, and delivers information on the state of the electrode itself addressing long-term electrode degradation.

Sensing mechanical deformation via ionic polymer metal composites: A primer

Ionic polymer metal composites (IPMCs) were discovered about twenty five years ago by Prof. Oguro and his team in Japan [1], and evidence about metalizing ionomer membranes dates even earlier [2]. Since their discovery, IPMCs have been the object of intensive research across the entire globe [3]-[5]. In its simplest form, an IPMC is constituted by a hydrated ionomeric membrane (that is, an electrically-charged polymer), which is neutralized by mobile counterions in a solution and plated by noble metal electrodes. IPMCs can be used as actuators and sensors, whereby a voltage applied across the electrodes will elicit mechanical deformation, and an imposed mechanical deformation will induce a measurable voltage across the electrodes.

Simultaneous Detection of Carbamates and Organophosphate Pesticides at Bare Boron-Doped Diamond Electrodes

Carbamate and organophosphate compounds are widely used pesticides because of their high insecticidal activity, and sometimes as nerve agents because of their crippling inhibition of the enzyme acetylcholinesterase (AChE)1. These compounds accumulate in the food chain and can hijack the nervous system of the target organisms indiscriminately. Traditional electrochemical methods of pesticide detection rely on layered structures atop noble metal or carbon electrodes to assist the loading of AChE, which produces currents proportional to its inhibition level. One of the clear advantages of boron-doped diamond (BDD) as an electrode material is its greater potential window in aqueous solutions, compared to conventional electrode materials2. This allows redox behaviour at extended potentials to be observed without damage to the electrode. Cyclic, differential-pulse, and square-wave voltammetric techniques were used to probe carbaryl (CB), carbofuran (CF), and malathion in Carmody buffers of pH 2–12. Oxidation of CF occurred at the three overpotentials 1.31 V, 1.44 V, and 1.69 V, and a broad reduction peak was observed at 1.10 V, referred against Ag|AgCl. Compared with the oxidation of CB at 1.35 V, these electrochemical differences allowed for simultaneous detection of both compounds. This non-enzymatic sensor demonstrated a linear calibration over a concentration range of 1–100 µM for CB (R=0.9834) and CF (R=0.9938). After exposure to 1 mM malathion, a reduction peak appears that is highly sensitive to pH, attributed to a complex carbon–oxygen adsorbate that is robust to aggressive cleaning methods and only removable by hydrogen plasma etching. This malathion modified surface may be advantageous in future applications such as pH sensing. The oxidised BDD demonstrated failsafe reproducibility, a linear response, and low detection limits at medically relevant concentrations. References Kostelnik, P. Kopel, A. Cegan, M. Pohanka, Sensors, 17 (2017) 676.V. Macpherson, Phys. Chem. Chem. Phys., 17 (2015) 2935-2949.

Paper-Based Disposable Molecular Sensor Constructed from Oxide Nanowires, Cellulose Nanofibers, and Pencil-Drawn Electrodes.

Progress toward the concept of "a trillion sensor universe" requires sensor devices to become more abundant, ubiquitous, and be potentially disposable. Here, we report a paper-based disposable molecular sensor device constructed from a nanowire sensor based on common zinc oxide (ZnO), a wood-derived biodegradable cellulose nanofiber paper substrate, and a low-cost graphite electrode. The ZnO nanowire/cellulose nanofiber composite structure is embedded in the surface of the cellulose nanofiber paper substrate via a two-step papermaking process. This structure provides a mechanically robust and efficiently bridged network for the nanowire sensor, while ensuring efficient access to target molecules and allowing reliable electrical contact with electrodes. The as-fabricated paper sensor device with pencil-drawn graphite electrodes exhibits efficient resistance change-based molecular sensing of NO2 as a model gas. The performance of our device is comparable to that of noble metal electrodes. Furthermore, we demonstrate cut-and-paste usability and easy disposal of the sensor device with its uniform in-plane sensing properties. Our strategy offers a disposable molecular sensing platform for use in future sensor network technologies.

A Solvent‐Free Solution: Vacuum‐Deposited Organic Monolayers Modify Work Functions of Noble Metal Electrodes

AbstractThe energy level alignment between organic semiconductors (OSCs) and the respective (metal) electrodes in organic electronic devices is of key importance for efficient charge carrier injection. For many years, researchers have attempted to control this energy level alignment by means of functional self‐assembled monolayers or the insertion of thin injection layers (made, e.g., of doped OCSs or pure dopants). The present work demonstrates an alternative to these approaches, namely the use of phthalocyanine monolayers as contact primers, which are deposited onto noble metal electrodes by means of vacuum deposition. It is shown that polar as well as non‐polar phthalocyanines modify the work functions of clean Au(111) and Ag(111) surfaces as a function of their coverage and thus enable quantitative control of the metal work functions. This behavior is successfully replicated for the respective polycrystalline metal surfaces and it is found that full monolayers can even withstand air exposure when protected by sacrificial multilayers, which are afterward removed by thermal desorption.

Copper Metallopolymer Catalyst for the Electrocatalytic Hydrogen Evolution Reaction (HER).

Conjugated polymers with stabilizing coordination units for single-site catalytic centers are excellent candidates to minimize the use of expensive noble metal electrode materials. In this study, conjugated metallopolymer, POS[Cu], was synthesized and fully characterized by means of spectroscopical, electrochemical, and photophysical methods. The copper metallopolymer was found to be highly active for the electrocatalytic hydrogen generation (HER) in an aqueous solution at pH 7.4 and overpotentials at 300 mV vs. reversible hydrogen electrode (RHE). Compared to the platinum electrode, the obtained overpotential is only 100 mV higher. The photoelectrochemical tests revealed that the complexation of the conjugated polymer POS turned its intrinsically electron-accepting (p-type) properties into an electron-donor (n-type) with photocurrent responses ten times higher than the organic photoelectrode.

Cost-efficient solar cells using nanocrystalline perovskite La (Fe and Mn) O3 and candle soot: Theory and experiment

In present investigation, co-precipitation as a simple, low temperature synthesis and low cost route was used to prepare nanocrystal perovskite La (Fe and Mn) O3 for solar cell application. The synthesized powders were characterized by XRD, SEM, PL, DRS, CV, EDS, and FTIR analysis. The photovoltaic behavior of prepared La (Fe and Mn) O3 perovskite as photo anode was also investigated, experimentally and theoretically. The best power conversion efficiency was experimentally obtained by LaFeO3 perovskite (0.07). Two different counter electrodes were applied: Pt electrode and an electrode prepared from a candle soot coated on the surface of FTO glass as a remarkable alternative material and process of noble metal electrode (Au or Ag) deposited by complicated vacuum technologies. In another stage, commercial electrolyte was used to enhance efficiency. These results indicate that there is a possibility to further increase the performance and efficiency of perovskite based cells.

Light Processing Enables Efficient Carbon-Based, All-Inorganic Planar CsPbIBr2 Solar Cells with High Photovoltages.

Inorganic halide perovskite CsPbIBr2 possesses the most balanced band gap and stability characters among all of the concerned analogs for carbon-based, all-inorganic solar cells that are free of any hole-transporting layers and noble-metal electrodes. Yet, the current CsPbIBr2 solar cells seem to deliver the lowest record efficiency. This is originally plagued by a serious energy loss ( Eloss) in the cells, which thus limits their open-circuit voltages ( Voc) severely. Herein, we demonstrate a light-processing technology that can overcome this obstacle successfully, by enabling the full-coverage, pure-phase CsPbIBr2 films featured with large grains, high crystallinity, and preferential [100] grains orientation, along with favorable electronic structure. It is achieved by the exposure of CsPbIBr2 precursor film formed in a conventional one-step spin-coating route to a simulated AM 1.5 G illumination before thermal annealing. The resulting carbon-based, all-inorganic planar cells give an optimized power conversion efficiency (PCE) of 8.60% with the Voc of 1.283 V. Notably, such an impressive Voc stands the highest value among all of the previously reported CsPbIBr2 solar cells; hence, its PCE exceeds nearly all of them. Therefore, our work suggests a new route to further improve the efficiency of low-cost, stable, and simple-fabrication CsPbIBr2 solar cells.

Performance of Surface‐Oxidized Ni3B, Ni2B, and NiB2 Electrocatalysts for Overall Water Splitting

AbstractThe development of efficient and earth‐abundant bifunctional electrocatalysts is of great important for energy conversion and storage technologies. Three surface oxidized nickel borides of Ni−B−O@Ni3B, Ni−B−O@Ni2B and Ni−B−O@NiB2 electrocatalysts have been prepared and investigated. Surface oxidation, which is inevitable for the bifunctional nickel borides, promotes the activity for the oxygen evolution reaction (OER), but leads to activity degradation for the hydrogen evolution reaction (HER). Meanwhile, boron is found to play a crucial role in the oxidation of nickel, facilitating the formation of an active intermediate for the OER. Ni−B−O@Ni3B turns out to be the best bifunctional electrocatalyst. An alkaline electrolyzer constructed using Ni−B−O@Ni3B electrodes as both anode and cathode has achieved a current density of 10 mA cm−2 at 1.58 V for overall water splitting with satisfied durability, rivaling the integrated noble metal electrode.

In-situ electrochemical activation of carbon fiber paper for the highly efficient electroreduction of concentrated nitric acid

An in-situ electrochemical activation method was developed to activate the carbon fiber paper (CFP) for the highly efficient concentrated HNO3 reduction. The defects and heteroatoms were introduced onto the surface of carbon fiber resulting in a significant improvement in the reactivity. Furthermore, the surface wettability of electrode was adjusted to enhance the accessibility of the active surface. Owing to these advantages, the activated-CFP electrode exhibits a higher current density (464.1 mA cm−2) for the electroreduction of 4 M HNO3 compared to the conventional Pt electrodes (75.39 mA cm−2). Based on scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and contact angle analysis, the HNO3 reduction mechanism on the activated CFP electrode was discussed. High activity as well as excellent electrochemical and chemical stability in the concentrated HNO3 make the activated-CFP as an effective alternative for noble-metal electrode in the future industrial applications.

Concentration cell-based potentiometric analysis for point-of-care testing with minimum background

One of the most critical problems of point-of-care testing is how to reduce the interference of background, especially under resource-limited conditions when sample pretreatment is not available. In this work we report a potentiometric method for point-of-care testing with minimum background. The method is based on the principles of a concentration cell which is a type of galvanic cells. It is an electrochemical cell having two carbon electrodes. The potential of each electrode is determined by ratio of a redox couple (i.e. Fe(CN)64−/3-) on the electrode surface. On one electrode, the adsorbed enzyme catalyzes the oxidation of analyte by Fe(CN)63− which produces Fe(CN)64−. The shift of the potential was because of the analyte as well as the background. In the other channel, no enzyme was present so that the shift of the potential, if any, is owing to the background. By measuring the potential difference between the two electrodes (i.e. voltage of the concentration cell), analyte can be quantitatively determined with most of the background eliminated. As the proof-of-concept analyte, blood glucose is quantitatively detected using a voltammeter with acceptable selectivity and accuracy. Noble metal electrodes that are indispensable for conventional electrochemical sensing are not required. All these features simplify the fabrication procedure and reduce the cost for the detection. Therefore, we believe it is promising for electrochemical point-of-care testing.

Alternative cost-effective electrodes for hydrogen production in saline water condition

For the sustainable clean and green energy, hydrogen is considered as one of the prominent renewable energy source which attracted increasing interests in recent years. To produce this, one of the cheapest method is water electrolysis. But several challenges in water electrolysis are, to reduce the maintenance cost, energy consumption and high cost of platinum electrode material. So, in search of an alternative low cost and efficient electrode material, researchers are modifying various metals electrodes to replace the noble metal electrodes. Stainless steel (SS 304) is one of the types of carbon steel material commonly used for various applications. The aim of the work is to explore the stainless steel (SS 304), annealed at high temperature, with and without “hydrogen and argon” environment and tested the samples for hydrogen production in sea water condition (3.5% NaCl). Cr2O3 and MnCr2O4 spinel oxide formation was observed over the surface of the electrodes after annealing process. From Raman, X-ray Photoelectron Spectroscopy (XPS) and electrochemical measurements it was observed that, the sample prepared under hydrogen and argon environment is stable when compared with the rest of the samples. Decrease in relative amount of chromium oxide was observed for the sample annealed in air environment. The rate of production of hydrogen prepared under “hydrogen and argon” environment is higher and the results are discussed.

Evaluation of in situ water electrochemical disinfection using novel carbon-based and noble metal electrodes

In this study, the morphology, chemical composition, and electrochemical characteristics of three carbon-based and three noble metal/alloy electrodes were evaluated. Measurement of free chlorine production was carried out using iodine–starch method. Measurement of hypochlorite production was performed using N,N-diethyl-p-phenylenediamine (DPD). The electro-catalytic activity of the electrodes was characterized using cyclic voltammetry (CV). Among the noble metals, the gold–palladium alloy electrode showed the best catalytic performance. Among the carbon-based electrodes, TiC showed the best catalytic performance. Scanning electron microscopy (SEM) images before and after reaction confirms the stability of the TiC electrode, proving its potential for long-term use. The chemical structure of the electrodes was characterized using X-ray photoelectron spectroscopy (XPS) and this showed that carbon electrodes present a trace graphene oxide structure (sp3 orbitals C–OH/C–O). Moreover, the modification of porous carbon by vacuum-assisted TiO2 impregnation indicates that the electronic state of TiC did not change due to impregnation with TiO2. In summary, the TiC carbon-based electrode shows high stability and potential for long use.

Counting surface redox sites in carbon-supported electrocatalysts by cathodic stripping of O deposited from N2O

Methods of determining in situ the electrochemically active surface area of bulk noble metal electrodes (e.g., underpotential deposition of a strongly interacting sorbent followed by columbic stripping) may not be appropriate for certain base metals supported on electroactive supports, such as carbon, because of the difficulty of finding a metal-specific titrant and because the support itself can contribute a very large background current. For example, the coulometric stripping of metal-selective sorbates, like carbon monoxide, works for the in situ characterization of certain electrode-supported metals (e.g. Pt, Pd) if applied carefully, but not for base metals, like Cu that do not strongly adsorb the titrant. Moreover, in scoping studies, we found that underpotential deposition of Tl on carbon-supported Cu failed to be selective for the copper. Here we present the use of gentle oxidation of the metal domains using N2O as the oxidant, followed by cathodic stripping of the surface oxide. The method compares approximately with XRD line broadening for characterizing ∼10 nm particles of Cu supported on graphite felt. More significantly, we show that the method usefully normalizes the rates of two electrochemical hydrogenation reactions: conversion of nitrobenzene to aniline and conversion of benzaldehyde to benzyl alcohol.

Enhanced efficiency and stability of fully air-processed TiO2 nanorods array based perovskite solar cell using commercial available CuSCN and carbon

In this study, commercial available inorganic p-semiconductor CuSCN and carbon was employed in replacing the expensive hole transport materials and noble metal electrode of the traditional perovskite solar cell, respectively. TiO2 compact layer and the mesoporous layer were also replaced by TiO2 nanorod arrays. The fully-air processed perovskite solar cells were easy to fabricate and demonstrated an enhanced efficiency and stability. The introduction of CuSCN improves the current density and the fill factor of the solar cell, thus leads to 29% increase in conversion efficiency. Intensity modulated photovoltage (IMVS) shows that the solar cell with CuSCN has a longer electron life time. Current attenuation curve shows that the current of the solar cell with CuSCN rises quicker and higher than that of the solar cell without CuSCN. The steady-state photoluminescence tests shows that the introduction of CuSCN layer enhances the separation of electrons and holes, thus reducing the recombination of electrons and holes. Electrochemical impedance spectroscopy (EIS) reveals that the solar cell with CuSCN has low transport resistance and high recombination resistance, thus leading to the slower electron recombination rates. In addition, study shows that the use of CuSCN and carbon displays high stability, and both kind of cells keep over 80% of the initial efficiency after 30 days without encapsulation. This method simplifies the perovskite solar cell fabrication process and opens a door toward the cheap, stable and printable solar cell.

Reliable Multivalued Conductance States in TaO x Memristors through Oxygen Plasma-Assisted Electrode Deposition with in Situ-Biased Conductance State Transmission Electron Microscopy Analysis.

Transition metal oxide-based memristors have widely been proposed for applications toward artificial synapses. In general, memristors have two or more electrically switchable stable resistance states that device researchers see as an analogue to the ion channels found in biological synapses. The mechanism behind resistive switching in metal oxides has been divided into electrochemical metallization models and valence change models. The stability of the resistance states in the memristor vary widely depending on: oxide material, electrode material, deposition conditions, film thickness, and programming conditions. So far, it has been extremely challenging to obtain reliable memristors with more than two stable multivalued states along with endurances greater than ∼1000 cycles for each of those states. Using an oxygen plasma-assisted sputter deposition method of noble metal electrodes, we found that the metal-oxide interface could be deposited with substantially lower interface roughness observable at the nanometer scale. This markedly improved device reliability and function, allowing for a demonstration of memristors with four completely distinct levels from ∼6 × 10-6 to ∼4 × 10-8 S that were tested up to 104 cycles per level. Furthermore through a unique in situ transmission electron microscopy study, we were able to verify a redox reaction-type model to be dominant in our samples, leading to the higher degree of electrical state controllability. For solid-state synapse applications, the improvements to electrical properties will lead to simple device structures, with an overall power and area reduction of at least 1000 times when compared to SRAM.