Cathodic Shift Research Articles

Utilizing a Siloxane-Modified Organic Semiconductor for Photoelectrochemical Water Splitting

We explore the potential of employing diketopyrrolopyrrole (DPP) based π-conjugated OSs as a hole transport layer material in heteroatom-doped hematite (Ti–Fe2O3/Ge–Fe2O3) photoanodes for efficient photoelectrochemical water splitting. The siloxane-modified π-conjugated polymer (PSi) with a high carrier mobility and crystallinity revealed great potential to extract holes by forming a built-in potential with hematite photoanodes while showing high stability in an alkaline electrolyte for photoelectrochemical water oxidation. Because of the easy hole extraction and subsequent fast hole transport property of the PSi interlayer between NiFe(OH)x and Ge-doped porous Fe2O3(Ge-PH), NiFe(OH)x/PSi/Ge-PH showed a 1.8-fold increase in photocurrent density (4.57 mA cm–2 at 1.23 VRHE) with a cathodic shift of the onset potential (0.735 VRHE) and good stability for 65 h compared to Ge-PH. This study demonstrates the successful use of inherently unstable π-conjugated OSs as a hole extracting/transport medium in a photoanode, addressing the intrinsic recombination issues of hematite for efficient and stable water splitting.

Ultrafast timescale charge carrier dynamics in nanocomposite hematite photoelectrodes

Hematite (α-Fe2O3) has been extensively studied as a candidate for solar water splitting. However, its overall efficiency in solar water splitting is currently low. In this study, Ti-doping, ZnFe2O4 shell and Co-Pi oxygen evolution catalysts (OECs) were applied on α-Fe2O3 nanocoral photoelectrode by forming a heterojunction to improve charge carrier separation. The current density of the Ti:Fe2O3/ZnFe2O4/Co-Pi nanocomposite photoelectrode at 1.23 VRHE was 3.6 mA/cm2. Moreover, the onset potential exhibited a cathodic shift of 0.85 VRHE, which improved the conversion efficiency to approximately 0.33 %. Transient absorption spectroscopy (TAS) was employed to investigate the yield and decay dynamics of photogenerated holes in the hematite-based photoelectrodes. The transient absorption data indicated different trends corresponding to the enhancement in the carrier separation due to band bending and holes transfer in the modified photoelectrodes. The enhancement in carrier separation was the origin of the high performance induced by long-lived carriers.

Combined Hydrogen Potentiometry and Electrochemical Impedance Spectroscopy Approach for Quantification of Oxygen Reduction Kinetics at Buried Metal/Organic Coating Interfaces

Oxygen reduction reaction (ORR) is considered a key electrochemical reaction, the kinetics of which are complex and challenging to quantify, even more at such buried metal/polymer interface. Here in this work, a novel approach independent of the polymer barrier property has been developed to quantitively characterize ORR kinetics using a combined hydrogen potentiometry (HP) and electrochemical impedance spectroscopy (EIS) approach. For the ORR measured using EIS on the front side of a bare Pd membrane exposed to an alkaline NaOH electrolyte, a 5-fold decrease in the charge transfer resistance (RCT) indicated the progress of ORR, in stark contrast to a corresponding 2-fold increase in inert N2 atmosphere. For a polymethyl methacrylate (PMMA)/Pd interface, a 30-fold decrease in RCT as compared to bare Pd correlated well with a cathodic shift of around 50 mV (1 pH unit) in the current-potential I(U) curve. At a molecularly tailored octane-thiol/Pd interface, ORR kinetics was highly inhibited, with the current-potential I(U) curve shifted in the cathodic direction by 190 mV, as compared to the Pd/PMMA interface at a charging (ORR) current of −25 μA cm−2. This could be successfully correlated to a 100-fold decrease in RCT value indicating interface sensitivity of this HP-EIS combined technique.

CoP-loaded BiVO4 for highly active and robust photocathodic protection of 304 stainless steel

Despite the narrow band gap and the suitable band edge position, the BiVO4 photoanode exhibits low metal anticorrosion performance due to inefficient charge separation and transfer. In this work, we introduce a CoP electrocatalyst with metal character on the BiVO4 surface by cyclic voltammetry to address this challenge, which greatly enhances the electron injection efficiency into the protected metal. The modified BiVO4 photoanode exhibits high solar water oxidation activity, resulting in a 123 mV cathodic shift on the self-corrosion potential of 304 stainless steel (304SS), enabling excellent metal protection. Additionally, the coupled composite photoanode shows high photo stability under light illumination, with only 8% decay on the open circuit potential after 51 h of photo-illumination. Our mechanism study shows that the CoP overlayer can act as the hole collector and electrocatalyst for water oxidation, and thus the BiVO4 valence band holes are effectively transferred to the CoP and subsequently to water. Such an improvement inhibits the charge recombination increasing the electron lifetime, and thus realizing the effective protection of 304SS. The present work offers a rather simple process that allows the effective deposition of CoP electrocatalyst on BiVO4 surfaces, which effectively protects metals from corrosion.

Comparative Analysis of the Interaction between the Antiviral Drug Umifenovir and Umifenovir Encapsulated in Phospholipids Micelles (Nanosome/Umifenovir) with dsDNA as a Model for Pharmacogenomic Analysis by Electrochemical Methods

In the present study, the electrochemical behavior of antiviral drug umifenovir (Umi) and umifenovir encapsulated in phospholipids micelles (nanosome/umifenovir, NUmi) were investigated for the first time on screen-printed electrodes modified by carbon nanotubes. We have shown that Umi can be electro oxidized around the potential of +0.4 V in the concentration range of 50–500 µM (R2 = 0.992). Non-overlapping signatures of DNA and umifenovir (10–150 µM) permit to register interaction between umifenovir (or umifenovir encapsulated in phospholipids micelles), purine, and pyrimidine heterocyclic bases of DNA separately. The type of interaction is most likely via electrostatic interactions and groove binding in drug-DNA formed complex, as was revealed based on the values of binding constants Kb and the cathodic shifts of oxidation potentials for heterocyclic bases with increasing Umi or NUmi concentration. The negative values of Gibbs free energy (ΔG) for all nucleobases confirm the process spontaneity. This study is the first one presenting the effect of antiviral drug umifenovir and umifenovir encapsulated in phospholipids micelles on dsDNA as a target of pharmacogenomics.

Study on the Interference Law of AC Transmission Lines on the Cathodic Protection Potential of Long-Distance Transmission Pipelines

Through inductive coupling, AC transmission lines can generate large amounts of voltage to buried oil and gas pipelines in areas with common corridors, posing a threat to the cathodic protection effect of pipelines. Therefore, this paper investigates the effect of AC transmission lines on the cathodic protection of long-distance pipelines through inductive coupling. COMSOL Multiphysics finite element simulation software is used to calculate the distribution of cathodic protection potential of long-distance pipelines under different voltage levels, parallel spacing, conductor-to-ground height, conductor arrangement and pipeline burial depth for normal operation of AC transmission lines. Comparison and analysis of the AC transmission line on the pipeline cathodic protection potential interference law is conducted. The results show that: 1. AC transmission lines cause serious electromagnetic interference with the pipeline cathodic protection system, which will cause the pipeline cathodic protection potential to shift out of the effective protection area. 2. The maximum value of the induced voltage of the pipeline will appear at the two ends of the pipeline, and the induced voltage of the pipeline in the middle position is 0. 3. The shift of the pipeline cathodic protection potential increases with the increase of voltage level and decreases with the increase of parallel spacing, conductor height and burial depth. The pipeline cathodic protection potential shift is highest when the wires are arranged horizontally and lowest when they are arranged in an umbrella shape.

Benchmarking of Aluminum Alloys Processed by High-Pressure Torsion: Al-3% Mg Alloy for High-Energy Density Al–Air Batteries

Aluminum–air batteries are an up-and-coming alternative for high-energy density storage. However, one of the main drawbacks is the self-corrosion of aluminum alloys in alkaline electrolytes, where the batteries perform best. For that reason, new aluminum alloys resistant to corrosion are required. Severe plastic deformation (SPD) techniques are versatile methodologies that result in metals with an ultrafine microstructure and can be used to prepare new alloys or modify their microstructure. In this study, 4N-Al (99,99%) and Al-2% Fe, Al-3% Mg, Al 1050, Al 5052, and Al 6063 alloys were studied as-received and after SPD by high-pressure torsion (HPT). We observed that the ultrafine-grained microstructure improved the resistance toward corrosion. However, the main determining factor in the resistance toward corrosion is the cathodic shift in the corrosion potential, as observed by mass loss and potentiodynamic polarization plots. Based on that, Al-3%Mg was chosen to be tested in an in-house designed aluminum–air cell with an alkaline gel electrolyte. The battery delivered up to 1407 mA h g–1, 1.7 V, and an operation time of 70 h at a current of 2 mA cm–2. Therefore, HPT represents an opportunity to easily prepare and benchmark new aluminum alloys for metal–air battery applications.

Modulation of Lewis and Brønsted Acidic Sites to Enhance the Redox Ability of Nb2O5 Photoanodes for Efficient Photoelectrochemical Performance.

Accelerated surface redox reaction and regulated carrier separation are the crux to the development of highly reactive oxide semiconductors for efficient photoelectrochemical water splitting. Here, we have selected Nb2O5 materials that combine unique surface acidity and semiconductor properties, and first used surface phosphorylation to change its surface acidic sites (Lewis and Brønsted acidic sites) to achieve efficient photoelectrochemical water splitting. The resulting photoanode born from this strategy exhibits a high photocurrent density of 0.348 mA/cm2 at 1.23 VRHE, which is about 2-fold higher than that of the bare Nb2O5, and a cathodic shift of 60 mV. Detailed experimental results show that the large increase in the Lewis acidic site can effectively modulate the electronic structure of the active sites involved in catalysis in [NbO5] polyhedra and promote the activation of lattice oxygen. As a result, higher redox properties and the ability to inhibit carrier recombination are exhibited. In addition, the weakening of the Brønsted acidic site drives the reduction of protons in the oxygen evolution reaction (OER) and accelerates the reaction kinetics. This work advances the development of efficient photoelectrochemical water splitting on photoanodes driven by the effective use of surface acidity and provides a strategy for enhancing redox capacity to achieve highly active photoanodes.

Computational fluid dynamics simulation of bubble hydrodynamics in water splitting: Effect of electrolyte inflow velocity and electrode morphology on cell performance

Efficient management of oxygen gas bubbles evolving at the photoanode is important for a good overall performance of a photoelectrochemical (PEC) cell. The process of formation, detachment, coalescence and rise affects the bubble residence time at or near the photoanode. A reduced bubble residence time promotes easier electrolyte access to the photoanode surface, thereby enhancing the oxygen evolution reaction (OER) kinetics. In this work, computational fluid dynamics (CFD) simulations using laminar flow and phase-field model in COMSOL Multiphysics are conducted to study the gas bubble hydrodynamics for different bubble configurations, sizes, and bubble gaps. CFD results predict enhanced bubble rise in the presence of forced convection, i.e., some electrolyte inflow velocity (u≠0m.s−1). Experimental results using hematite as the model electrode also show a higher photocurrent density (ca. 4.33 mA.cm−2 at 2 V vs. RHE) for u = 0.1 m.s−1, compared to that without flow (3.5 mA.cm−2 at 2 V vs. RHE). This indicates improved access of electrolyte at the electrode surface and faster OER. Further, CFD simulations for electrode morphology effects show a reduced bubble adhesion for hydrophilic hematite nanorod arrays compared to planar photoanode, due to capillary wicking. The continuous contact film detaches and results in a reduced blockage of active sites at the bubble base, thereby enhancing the PEC performance for the nanorod arrayed morphology. Here too, experimental results show a four-fold increase in photocurrent density (ca. 0.1 mA.cm−2 at 1.5 V vs. RHE) and a 210 mV cathodic shift in onset potential for nanorods, compared to planar electrodes (0.025 mA.cm−2 at 1.5 V vs. RHE). A significant reduction in charge transfer resistance is observed for the former, implying better OER kinetics. The results obtained help in the understanding of transient processes involving O2 bubble hydrodynamics and electrolyte usage efficiency in a PEC reactor.

Modulating the Geometry of the Carbon Nanofiber Electrodes Provides Control over Dopamine Sensor Performance.

One of the major challenges for in vivo electrochemical measurements of dopamine (DA) is to achieve selectivity in the presence of interferents, such as ascorbic acid (AA) and uric acid (UA). Complicated multimaterial structures and ill-defined pretreatments have been frequently utilized to enhance selectivity. The lack of control over the realized structures has prevented establishing associations between the achieved selectivity and the electrode structure. Owing to their easily tailorable structure, carbon nanofiber (CNF) electrodes have become promising materials for neurobiological applications. Here, a novel yet simple strategy to control the sensitivity and selectivity of CNF electrodes toward DA is reported. It consists of adjusting the lengths of CNF by modulating the growth phase during the fabrication process while keeping the surface chemistries similar. It was observed that the sensitivity of the CNF electrodes toward DA was enhanced with the increase in the fiber lengths. More importantly, the increase in the fiber length induced (i) an anodic shift in the DA oxidation peak and (ii) a cathodic shift in the AA oxidation peak. As the UA oxidation peak remained unaffected at high anodic potentials, the electrodes with long CNFs showed excellent selectivity. Electrodes without proper fibers showed only a single broad peak in the solution of AA, DA, and UA, completely lacking the ability to discriminate DA. Hence, the simple strategy of controlling CNF length without the need to carry out any complex chemical treatments provides us a feasible and robust route to fabricate electrode materials for neurotransmitter detection with excellent sensitivity and selectivity.

Passivation of Hematite by a Semiconducting Overlayer Reduces Charge Recombination: An Insight from Nonadiabatic Molecular Dynamics.

Hematite (α-Fe2O3) is a promising photoanode material for photoelectrochemical water splitting. Surface-passivating layers are effective in improving water oxidation kinetics; however, the passivation mechanism is not fully understood due to the complexity of interfacial reactions. Focusing on the Fe-terminated Fe2O3 (0001) surface that exhibits surface states in the band gap, we perform ab initio quantum dynamics simulations to study the effect of an α-Ga2O3 overlayer on charge recombination. The overlayer eliminates surface states and suppresses charge recombination 4-fold. This explains in part the observed cathodic shift in the onset potential for water oxidation. The increased charge carrier lifetime is an outcome of two factors, energy gap and electron-vibrational coupling, with a positive contribution from the former but a negative contribution from the latter. This work presents an advance in the atomistic time-domain understanding of the influence of surface passivation on charge recombination dynamics and provides guidance for designing novel α-Fe2O3 photoanodes.

NiFePB-modified ZnO/BiVO4 photoanode for PEC water oxidation.

Photoelectrochemical (PEC) water splitting has been recognized as the most promising approach for directly converting solar energy into chemical energy, and substantial efforts have been made to develop a highly efficient and low-cost photoanode for enhancement of PEC water splitting efficiency due to sluggish water oxidation reaction kinetics. A ternary NiFePB-modified ZnO/BiVO4 heterojunction photoanode was simply assembled by low-temperature hydrothermal, metal-organic decomposition and electrodeposition methods to improve the water splitting efficiency; its photocurrent density for water oxidation reached 1.66 mA cm-2 at 1.23 V (vs. RHE); in comparison, that of ZnO is only 0.4 mA cm-2. The onset potential manifests a cathodic shift of ∼283 mV compared to ZnO. The IPCE and the ABPE respectively are 3.1 and 6.4 times those of ZnO, respectively. This improvement is ascribed to the efficient separation of photogenerated electrons and holes by the formation of a heterojunction between ZnO and BiVO4 and the enhancement in the oxygen evolution reaction kinetics by the decoration of the co-catalyst NiFePB as a hole acceptor.

Meso-pore generating P doping for efficient photoelectrochemical water splitting

Hematite (Fe2O3) has been widely used as a photoanode in photoelectrochemical water splitting (PEC) for green hydrogen production. Here, for the first time, we investigate how a simple in-situ phosphorus (P) doping strategy improves the overall PEC performance of hematite with a systematic analysis of the various effects on the PEC performance. By introducing enriched FePO4 regions on the Ti-doped FeOOH surface and subsequent high-temperature annealing via P-doping, meso-porous P,Ti co-doped Fe2O3 (P,Ti-Fe2O3) nanorods were fabricated. P,Ti-Fe2O3 exhibited four-fold and two-fold increased BET surface area and electrical active area, respectively, compared to that of Ti-Fe2O3. Benefiting from the nano-structuring and efficient P doping effects [e.g., increased carrier density (Nd=3.48168 ×1020 cm−3), enhanced charge separation (ηbulk= 38.7% and ηsurface= 79.1%), and steeper band bending (Wd=3.910 nm)], the resulting P,Ti-Fe2O3 photoanode exhibited 94% improved photocurrent density of 2.50 mA cm−2 compared to that of Ti-Fe2O3 (@ 1.23 VRHE) under 1 sun illumination. With the deposition of the NiFeOx cocatalyst, the NiFeOx/P,Ti-Fe2O3 photoanode exhibited excellent photocurrent density of 3.54 mA cm−2 (@ 1.23 VRHE) with a remarkable cathodic shift (180 mV) of the onset potential, marking the highest value among P doped hematite studies. This study suggests a new paradigm of P doped hematite with mesopores and gradient doping properties affordable in a cost-efficient way, achieving an excellent PEC water splitting performance.

Magnetron Sputtered Al Co-Doped with Zr-Fe2O3 Photoanode with Fortuitous Al2O3 Passivation Layer to Lower the Onset Potential for Photoelectrochemical Solar Water Splitting

In this paper, we investigate the magnetron sputtering deposition of an Al-layer on Zr-doped FeOOH (Zr-FeOOH) samples to fabricate a Zr/Al co-doped Fe2O3 (Al-Zr/HT) photoanode. An Al-layer is deposited onto Zr-FeOOH through magnetron sputtering and the thickness of the Al deposition is regulated by differing the sputtering time. Electrochemical impedance spectroscopy, intensity-modulated photocurrent spectroscopy, Mott-Schottky and time-resolved photoluminescence spectra analyses were used to study, in depth, the correlations between sputtered Al-layer thicknesses and PEC characteristics. High-temperature quenching (800 °C) assists in diffusing the Al3+ in the bulk of the Zr-doped Fe2O3 photoanode, whilst an unintended Al2O3 passivation layer forms on the surface. The optimized Al-Zr/HT photoelectrode achieved 0.945 mA/cm2 at 1.0 VRHE, which is 3-fold higher than that of the bare Zr/HT photoanode. The Al2O3 passivation layer causes a 100 mV cathodic shift in the onset potential. Al co-doping improved the donor density, thus reducing the electron transit time. In addition, the passivation effect of the Al2O3 layer ameliorated the surface charge transfer kinetics. The Al2O3 passivation layer suppressed the surface charge transfer resistance, consequently expediting the hole migration from photoanode to electrolyte. We believe that the thickness-controlled Al-layer sputtering approach could be applicable for various metal oxide photoanodes to lower the onset potential.

Gradient Si- and Ti-doped Fe2O3 hierarchical homojunction photoanode for efficient solar water splitting: Effect of facile microwave-assisted growth of Si-FeOOH on Ti-FeOOH nanocorals

The construction of a homojunction is an effective approach for addressing issues such as slow charge separation and charge-transfer kinetics in photoanodes. In the present work, we designed a gradient Si- and Ti-doped Fe2O3 homojunction photoanode to improve the photoelectrochemical (PEC) performance of a Ti-doped Fe2O3 photoanode. Ti-FeOOH nanocorals were synthesized using a hydrothermal process, and Si-FeOOH was grown on Ti-FeOOH nanocorals using a rapid and facile microwave-assisted (MW) technique. By varying the MW irradiation time, the thickness of the Si/Ti:Fe2O3 photoanode was adjusted and an optimized 3-Si/Ti:Fe2O3 photoelectrode was achieved with a significantly enhanced photocurrent density (1.37 mA cm−2 at 1.23 V vs. RHE) and a cathodic shift of the onset potential (150 mV) compared with that of bare Ti-Fe2O3. This enhanced PEC performance can be ascribed to homojunction formation and Si gradient doping. The Si dopant increased the donor concentration and the formation of a homojunction improved the intrinsic built-in electric field, thereby promoting charge separation and charge transfer. Furthermore, the as-formed homojunction passivated the surface-trapping states, consequently improving the charge transfer efficiency (60% at 1.23 VRHE) at the photoanode/electrolyte interface. These findings could pave the way for the microwave-assisted fabrication of diverse efficient homojunction photoanodes for PEC water splitting applications.

Promoting nickel oxidation state transitions in single-layer NiFeB hydroxide nanosheets for efficient oxygen evolution

Promoting the formation of high-oxidation-state transition metal species in a hydroxide catalyst may improve its catalytic activity in the oxygen evolution reaction, which remains difficult to achieve with current synthetic strategies. Herein, we present a synthesis of single-layer NiFeB hydroxide nanosheets and demonstrate the efficacy of electron-deficient boron in promoting the formation of high-oxidation-state Ni for improved oxygen evolution activity. Raman spectroscopy, X-ray absorption spectroscopy, and electrochemical analyses show that incorporation of B into a NiFe hydroxide causes a cathodic shift of the Ni2+(OH)2 → Ni3+δOOH transition potential. Density functional theory calculations suggest an elevated oxidation state for Ni and decreased energy barriers for the reaction with the NiFeB hydroxide catalyst. Consequently, a current density of 100 mA cm–2 was achieved in 1 M KOH at an overpotential of 252 mV, placing it among the best Ni-based catalysts for this reaction. This work opens new opportunities in electronic engineering of metal hydroxides (or oxides) for efficient oxygen evolution in water-splitting applications.

(Invited) Non-Metal P Doping for Efficient Water Splitting

Here, we investigate how a simple in-situ phosphorus (P) doping strategy improves the overall PEC performance of hematite. By introducing enriched FePO4 regions on the Ti-doped FeOOH surface and subsequent high-temperature annealing, P,Ti co-doped Fe2O3 (P,Ti-Fe2O3) nanorods were fabricated. P,Ti-Fe2O3 not only increased the conductivity by creating oxygen vacancies but also generated a porous structure inside the hematite. Benefiting from the efficient P doping effects, the resulting P,Ti-Fe2O3 photoanode exhibited 94% improved photocurrent density compared to that of Ti-Fe2O3 (@ 1.23 VRHE) under 1 sun illumination. After applying the co-catalyst, NiFeOx/P,Ti-Fe2O3 showed significantly enhanced photocurrent density (3.54 mA cm-2 at 1.23 VRHE) with a 108 mV cathodic shift. Our study suggests a new approach for achieving porous hematite and a highly efficient PEC system by a simple and cost-effective nonmetal P-doping method.

Fluoride ion sensing with an acridinium borane

With our continuing interest in the chemistry of cationic boranes, we have synthesized the tetrafluoroborate salt of 1-dimesitylboron-4-( N-methyl-9-acridinium)-phenylene, which acts as a turn-on fluoride anion sensor, visibly changing from yellow to orange upon binding fluoride. To understand this reactivity, we spectroscopically and computationally analyzed the cation and fluoroborate adduct. Ultraviolet–visible spectroscopy and time-dependent density functional theory calculations revealed the basis of the color change to be a low energy redshift in a intramolecular charge transfer band. Electrochemical studies were undertaken to further probe this system. Cyclic voltammetry indicated a reversible one-electron reduction for the cation and a cathodic shift of −0.12 V in the first reduction wave upon fluoride binding. Chemical reduction of the cation yielded the acridine borane radical, which was verified by electron paramagnetic resonance spectroscopy.

Bisaryl and Bisalkynyl Diruthenium (III,III) Compounds Based on an Electron-Deficient Building Block.

Reported herein is a new series of diruthenium(III,III) bisalkynyl and bisaryl diruthenium(III,III) compounds supported with 2-amino-3-(trifluoromethyl)pyridinate (amtfmp). Using Ru2(amtfmp)4Cl2 from a modified preparation, cis 2:2 Ru2(amtfmp)4(C≡CPh)2 (1), cis 2:2 Ru2(amtfmp)4(Ph)2 (2), and 3:1 Ru2(amtfmp)4(Ph)2 (3) were synthesized via a lithium-halogen exchange reaction using LiC2Ph and LiPh, respectively. Compounds 1-3 are all Ru2(III,III) species with a ground-state configuration of π4δ2(π*)4 (S = 0) and were characterized via mass spectrometry, electron absorption and 1H/19F NMR spectroscopies, and voltammetry. The molecular structures of 1-3 were established using single-crystal X-ray diffraction analysis, and preliminary density functional theory analysis was performed to elaborate the electronic structures of 1 and 2. Comparisons of the electrochemical properties of 1-3 against the Ru2(amtfmp)4Cl2 starting material reveal cathodic shifts of the Ru27+/6+ oxidation and the Ru26+/5+ and Ru25+/4+ reduction potentials. In comparison to related Ru2(III,III) bisalkynyl and bisaryl compounds, the electrode potentials for 1-3 are anodically shifted up to ca. 0.95 V, highlighting the strong electron-withdrawing nature of the amtfmp ligand.

Hematite decorated with nanodot-like cobalt (oxy)hydroxides for boosted photoelectrochemical water oxidation

Photoelectrochemical (PEC) water splitting has been considered as an alternative process to produce green hydrogen. However, the energy conversion efficiency of PEC systems was still limited by the inefficient photoanode. Cocatalysts decoration is regarded as an efficient strategy for improving PEC performance of photoanode. In this work, nanodot-like cobalt (oxy)hydroxides was rationally decorated on hematite to fabricate CoOOH/Fe2O3 photoanode. The resulted CoOOH/Fe2O3 exhibits a high photocurrent density of 1.92 mA cm−2 at 1.23 V vs. RHE, which is 2.6 times than that of bare Fe2O3. In addition, the onset potential displays a cathodic shift of ca. 110 mV, indicating that CoOOH can efficiently accelerate water oxidation kinetics over Fe2O3. The comprehensive PEC and electrochemical characterizations reveal that CoOOH could not only provide abundant accessible Co active sites for water oxidation, but also could passivate the surface states of Fe2O3, thus increase the carrier density and decrease the interfacial resistance. As a result, the PEC water oxidation performance over Fe2O3 was significantly boosted. This work supports that the roles of CoOOH cocatalyst is generic and such CoOOH could be used for other semiconductor-based photoanodes for outstanding PEC water splitting performance.