High Electrochemical Active Surface Area Research Articles

Cobalt Hydroxide Spindle Nanosheet Amorphous Electrocatalysts via In‐Situ Fast Reduction Release/Oxidization Mechanistic Method for Efficient Overall Water Electrolysis

AbstractWater electrolysis focused with electricity or sunlight is one of the sustainable methods to produce hydrogen; this helps to address the global energy demand whereas sluggish OER and HER kinetic barriers hamper this process. Here, we report an earth abundant Co(OH)2 spindle nanosheet electrocatalyst synthesized via surfactant with boron‐assisted release/oxidize mechanistic process and employed it as a bifunctional electrocatalyst (OER/HER) with small overpotential (258 mV/156 mV), low Tafel slope (78 mV dec−1/71 mV dec−1), higher turnover frequency (0.235 s−1/0.100 s−1) and low charge transfer resistance (4.7 Ω). The higher electrochemical active surface area (45 cm2) of the catalyst exploits the potential electrocatalyst nature with overall cell voltage 1.64 V at 10 mA cm−2.

Modulating electrodeposition of ultralow Pt into 2D MoCu-POMOF-derived MoO2/MoOC for boosted hydrogen evolution reaction

Electrochemical water splitting is regarded as a promising technology for production of high purity, high volume hydrogen. It is critical to create robust and highly active electrocatalysts in order to minimize the cost of hydrogen generation and enable large-scale commercial production. In this work, a new 2D MoCu-POMOF, [Cu(4-pyz)]4@(PMo12O40) (4-pyz = 4-(pyridin-4-yl)benzoic acid) was prepared by a simple hydrothermal method, in which PMo12 nanocluster was encapsulated into cavity of 2D Cu-MOF. The successful establishment of the model in addition to the goal of uniformly dispersed Mo sources target oxygen-rich PMo12 nanoclusters can also provide rich Mo source and self-oxidative properties for MoO2 formation. Cu-MOF provides a special layered structure, which ensures the integrity and stability of the structure and provides a rich C source for pyrolysis and improves the conductivity. Ultralow Pt nanoparticles can reduce free energy of hydrogen evolution, which are embedded in MoO2/MoOC with porous structure and high electrochemical active surface area. MoO2/MoOC and highly dispersed Pt nanoparticles synergistically promote the HER catalysis. Pt@MoO2/MoOC demonstrated the excellent HER activity with a low overpotential of 98.99 mV vs. RHE. This work yielded highly active and high stability molybdenum-based HER electrocatalysis and provides the potential for energy conversion.

Enhanced Methanol Oxidation in Alkaline Media on Electrodeposited Ni Electrodes by Morphological and Crystallographic Evolution

This research aims at exploiting the electrocatalytic behaviour of nano-crystalline nickel electrodes electrodeposited by different techniques including direct current (DC), pulse current (PC), or pulse reversal current (PRC) for methanol electrooxidation in alkaline solutions. We understand that PC electrodeposition forms pyramidal shaped grains with a preferential Bragg diffraction peak of (111), whereas PRC produced refined spherical grain morphology with a strong (200) diffraction peak. However, DC electrodeposition exhibits an intermediate morphology and crystalline structure. Cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) show that PRC electrodeposition develops Ni electrodes with better electrocatalytic activity for methanol electrooxidation than other two nickel electrodes. Based on the CV curve, the current density for Ni prepared by PRC electrodeposition methods is about 75.26 mA.cm−2, which is higher than those of DC and PC methods. This higher activity of PRC electrodeposited nickel is attributed to the low charge transfer resistance confirmed by Nyquist plots. We attributed this behavior to the (200)-oriented crystallographic texture, spherical grain morphology, and consequently the high electrochemical active surface area of this nickel electrode. This work reveals the importance of surface morphology and crystallography on the electrocatalytic behaviour of nickel electrodes for electrochemical energy devices.

Electrochemical sensor based on MOF derived LaFexNi(1-x)O3 using carbon spheres as the template for simultaneous determination of p-aminophenol and paracetamol

Using metal–organic frameworks (MOFs) as the precursor and carbon spheres as the template, LaFexNi(1-x)O3 (x = 1, 0.8, 0.6, 0.4, 0.2, 0) perovskite-type oxides were synthesized. The structure, morphology and valence state of as-prepared perovskite-type oxides were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, and X-ray photoelectron spectroscopy. Cyclic voltammetry and electrochemical impedance techniques were used to study the effect of Ni-doping ratios on the electrocatalytic performance of perovskite. The differential pulse voltammetry was used to measure the content of p-aminophenol (PAP) and paracetamol (PAT) through the LaFe0.6Ni0.4O3 modified glassy carbon electrode. The experiment shows that among LaFexNi(1-x)O3 (x = 1, 0.8, 0.6, 0.4, 0.2, 0) perovskite-type oxides, LaFe0.6Ni0.4O3 was best electrode material due to its low charge transfer resistance and high electrochemical active surface area. The linear ranges of PAP and PAT were both 1.0–100.0 μM under optimized conditions, while the detection limits were 0.111 and 0.162 μM (S/N = 3), respectively. The practicality of the suggested sensor was explored through the simultaneous detection of PAP and PAT in real samples, and satisfactory findings in acetaminophen pills were obtained.

Oxygen reduction stability of graphene-supported electrocatalyst: Electrochemical and morphological evidences

Graphene has been proposed as support or as co-support for Proton Exchange Membrane Fuel cells (PEMFCs) electrocatalysts due to its high electronic conductivity, corrosion stability and high specific surface area compared to common carbon blacks, such as Vulcan. Despite such outstanding properties, comprehensive studies on long-term stability of graphene-supported Oxygen Reduction Reaction (ORR) catalysts are still unavailable or limited.The stability of graphene as support is now studied and compared with carbon black in terms of electrochemical performance and degradation mechanisms. Catalytic layers with Pt/G were prepared and subjected to a set of three different Accelerated Stress Tests (ASTs): cycling at high potentials, Open Circuit Potential (OCP) holding and cycling at low potentials. This study aims to assess if and why graphene is a better candidate as support.The Pt/G catalyst outperformed the reference catalyst in all ASTs, delivering both higher electrochemical active surface area (ECSA) and ORR mass-specific activity. Such electrochemical performance was correlated with morphological evidences associated to the support itself and with Pt nanoparticles.

Nanocomposite of nickel benzene‐1,3,5‐tricarboxylic acid metal organic framework with multiwalled carbon nanotubes: A robust and effective electrocatalyst for oxygen evolution reaction in water splitting

In the current era, the development of robust, eco‐friendly, and highly efficient electrocatalysts for generating hydrogen energy by water electrolysis has become a major challenge. This work explains the electrocatalytic performance of cost‐effective and amiable novel Ni‐BTC‐MWCNTs‐a as an active and effective electrocatalyst for OER in alkaline media. The catalytic activity of the nanocomposite is increased by heat treatment at 400°C temperature for 3 h. Systematic morphological and structural characterization studies of solvothermal synthesized materials were carried out by X‐ray powder diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy technique, scanning electron microscopy (SEM) analysis, and energy dispersive X‐ray spectroscopy (EDS) analysis techniques. Metal–organic framework (MOF)‐based composites exhibit improved catalytic performance owing to the synergistic effect of Nickel BTC MOF, MWCNTs support, and high‐temperature annealing (400°C). Among all as‐synthesized materials, the annealed Ni‐BTC‐MWCNT‐a exhibits admirable catalytic performance for oxygen evolution reaction (OER) at low value for over potential (η) 243 m V, small Tafel slope value 57 mV dec−1, smaller charge transfer resistance (0.274 Ω), and higher electrochemical active surface area (2000 cm2) with maximum durability for 23 h and utilized as auspicious alternate with excellent catalytic activity in water splitting OER process for producing hydrogen energy at large scale other than highly expensive electrocatalysts of Ir, Ru, Pd, and Pt oxides.

High Performance Carbon Material Prepared from Phalsa Using Mild Pyrolytic Process towards Photodegradation of Methylene Blue under the Irradiation of UV Light

In this study, we have used a mild pyrolytic process for the synthesis of luminescent carbon material from phalsa (Grewia asiatica Linn) and utilized it for the photodegradation of methylene blue (MB) in aqueous solution under the irradiation of ultraviolet (UV) light. The carbon material was found to be graphitic in nature and with carbon dot-like properties as demonstrated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DLS), and UV-visible techniques. The prepared carbon material was further studied for the elucidation of functional groups through Fourier transform infra-red (FTIR) spectroscopy. The carbon material exhibits the nanostructured phase which makes it a high surface area material for useful surface reactions. Different photodegradation aspects were investigated, such as initial dye concentration, catalyst dose, effect of pH of dye solution, reusability, electrochemical active surface area (ECSA), and charge transfer and scavenger. Optimum conditions of 15 mg carbon material, initial dye concentration of 2.3 × 10−5 M solution, and pH 5 of dye solution gave the highest outperformance degradation efficiency. The degradation mechanism of MB in aqueous solution was dominated by the hydroxyl radicals as verified by the scavenger study. The reaction kinetics of MB degradation was followed by the pseudo first order kinetics and highest values of rate constants in the low initial dye concentration and the acidic pH of the MB solution. Significantly, the carbon material prepared from phalsa was found to be highly stable, as proven by the reusability experiments. Furthermore, the high ECSA and low charge transfer resistance of carbon material enabled it to have better performance. The use of mild pyrolytic process for the preparation of high performance luminescent carbon material from the biomass could be a great roadmap for the synthesis of a new generation of carbon materials for a wide range of applications including bio-imaging, catalysis, energy conversion and environmental applications.

Investigation of the effects of supporting material modification on the nucleation behavior of Pt catalysts

The presence of stable support material allows catalysts to operate for longer periods under harsh conditions. Although carbon is widely preferred as a supporting material for platinum (Pt) catalysts, the oxidizing problem at high overpotentials causes the catalyst dissolution and reduces the surface area. However, different functional groups on the supporting material surface provide a more homogeneous and rapid reduction of metal cation. Therefore, the use of composites consisting of conductive polymers and carbon structures gains importance. In this study, carbon modification is performed by polyaniline- and 4-Fluoroaniline and synthesized samples are physically and electrochemically characterized. The actual catalytic performances of these catalysts are investigated in a single-cell fuel cell. Characterization studies showed Pt particles distributed more homogeneously on 4F-PANI-C and have smaller grain sizes. CV results support that Pt/4F-PANI-C has a relatively higher electrochemical active surface area. This situation remains valid after the ADT tests. Finally, the MEA performances show that both the power and current density of the Pt/4F-PANI-C catalyst are higher than the other samples.

Electrodeposition of Stable Noble-Metal-Free Co-P Electrocatalysts for Hydrogen Evolution Reaction.

Hydrogen production via water splitting has been extensively explored over the past few decades, and considerable effort has been directed toward finding more reactive and cost-effective electrocatalysts by engineering their compositions, shapes, and crystal structures. In this study, we developed hierarchical cobalt phosphide (Co-P) nanosphere assemblies as non-noble metal electrocatalysts via one-step electrodeposition. The morphologies of the Co-P nanostructures and their electrocatalytic activities towards the hydrogen evolution reactions (HER) were controlled by the applied potentials during electrodeposition. The physicochemical properties of the as-prepared Co-P nanostructures in this study were characterized by field-emission scanning electron microscopy, X-ray photoemission spectroscopy and X-ray diffraction. Linear sweep voltammetry revealed that the Co-P grown at -0.9 V showed the best HER performance exhibiting the highest electrochemical active surface area and lowest interfacial charge transfer resistance. The Co-P electrocatalysts showed superior long-term stability to electrodeposited Pt, indicating their potential benefits.

Rational design of dysprosium cobalt oxide decorated on flower-like molybdenum disulfide: Development of an electrochemical sensor for antipsychotic drug promazine

The construction of perovskite oxides and metal chalcogenide nanocomposites has been employed to develop electrochemical sensors with outstanding sensitivity and low detection limit. In this work, we have successfully synthesized dysprosium cobalt oxide (DCO) encapsulated with molybdenum disulfide (MS) via ultrasonication way, which is employed for the electrochemical determination of antipsychotic drug promazine (PMZ). The as-prepared DCO/MS nanocomposite was scrutinized by different techniques such as X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) analysis, field emission scanning electron microscope (FE-SEM), and high-resolution transmission electron microscope (HR-TEM). Further, the prepared nanocomposites were modified on a glassy carbon electrode (GCE) surface and electrochemical activity was inspected through cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in 0.1 M phosphate buffer solution (PB) with a potential window of 0.0–0.9 V. As a result, DCO/MS promotes superior electrochemical performance because of high electrochemical active surface area (0.396 cm2), good conductivity, and synergetic effect. The developed electrochemical sensor exhibits a broad linear range (0.002 – 695.6 μM) and the lowest detection limit of 0.005 µM, excellent sensitivity, repeatability, and reproducibility. Finally, the fabricated sensor was successively used for the real-time detection of PMZ in environmental and biological samples with feasible recoveries.

Self-supporting NiMo-Fe-P nanowire arrays as bifunctional catalysts for efficient overall water splitting.

Developing efficient bifunctional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalysts is beneficial for simplifying the design of electrolytic cells and reducing the cost of device manufacturing. Herein, a metal phosphide nanoarray (NiMo-Fe-P) electrocatalyst was designed by in situ ion exchange and low-temperature phosphating to promote overall water splitting in 1 M KOH. NiMo-Fe-P demonstrates superb HER and OER activities as reflected by the low overpotentials of 73.1 mV and 215.2 mV, respectively, at a current density of 10 mA cm-2. The addition of Fe changes the electronic structure of Ni, which is conducive to the chemisorption of oxygen-containing intermediates and reduces the energy barrier for water decomposition. Besides, the metal phosphide not only acts as the active site of the HER, but also improves the conductivity of the catalyst. Furthermore, nanowire arrays and the small particles generated on their surfaces provide a high electrochemical active surface area (ECSA), which was beneficial for the exposure of active sites. Attributed to these advantages, the cell voltage of the water electrolyzer constructed with NiMo-Fe-P as both the cathode and anode is only 1.526 V at 10 mA cm-2, and it maintains excellent stability for 100 h with near negligible changes in potential.

Co-deposition of Co-Ni alloy catalysts from an ethylene glycol system for the hydrogen evolution reaction.

The preparation of active, stable and low-cost non-noble electrocatalysts for the hydrogen evolution reaction (HER) using the electrochemical water splitting process is crucial for the promotion of sustainable energy. In this study, Co-Ni alloys with various Co contents are prepared using a galvanostatic method and the co-deposition behavior of Co2+ and Ni2+ in ethylene glycol (EG) is reported. These results indicate that the presence of additional Ni2+ species can accelerate the Co-Ni co-deposition process and Co2+ species in the system can inhibit the reduction of Ni2+. Moreover, the two effects are improved with an increase in Ni2+ or Co2+ species concentration in the EG system, respectively. Chronoamperometry records show that the Co-Ni electro-crystallization mechanism is one of 3D instantaneous nucleation and growth. Moreover, the Co-Ni alloy with 59.46 wt% Co exhibits high electrocatalytic activity for HER with an overpotential of 133 mV at 10 mA cm-2 in 1 M KOH due to a high value of electrochemical active surface area (ECSA) (955.0 cm2). Therefore, the Co-Ni alloy electrocatalyst obtained from the EG system could be a promising candidate for practical hydrogen production.

Cavitation regulated sonochemical synthesis of flexible self-supported CuO@PDA/CC electrode for highly sensitive glucose sensor

Sonochemical synthesis is recognized as a promising high-efficiency method for fabricating transition metal oxides (TMOs) based flexible self-supported electrodes as nonenzymatic glucose sensor. However, it is still a challenge to obtain TMOs self-supported electrodes with well-controlled TMOs nanostructure and desirable interfacial properties via a sonochemical approach because of the uncontrollability of transient cavitation. In this study, CuO@polydopamine (PDA) nanoparticles (NPs) are in situ grown onto carbon cloth (CC) to fabricate CuO@PDA/CC self-supported electrode via a sonochemical process. The sonochemically synthesized PDA not only stabilized the transient cavitation intensity, but also regulated the growth of CuO due to the strong chelating ability between Cu2+ and catechol groups from PDA. It is determined that the mean size of CuO@PDA NPs on the CuO@PDA/CC electrode is less than 100 nm with a narrow size distribution. Attributed to high electrochemical active surface area (4.61 mF cm−2) and low interface resistance (2.35 Ω), CuO@PDA/CC electrode displays excellent electrochemical performance as a glucose sensor with high sensitivity of 1.843 μA cm−2 mM−1 in a wide linear range up to 4.985 mM and excellent stability. This work provides a facile approach to fabricating the flexible self-supported electrodes with well-controlled nanostructure and desirable interfacial properties for high-performance electrochemical sensors via regulating the transient cavitation intensity in the sonochemical process.

Gold nanoparticles decorated covalent organic polymer as a bimodal catalyst for total water splitting and nitro compound reduction

The design and construction of a bimodal catalyst with magnificent performance and high stability is a debatable one for total water splitting and nitro compound reduction. Herein, we report the synthesis of a covalent organic polymer network based on 1,4-phenylenediamine based covalent organic polymer (PD-COP) and its decoration with Au nanoparticles (Au NPs) as well as their confirmation using various analytical and surface techniques. The electrocatalytic activity toward total water-splitting reaction (OER and HER) in KOH solution (1.0 M) was investigated. In addition, the reduction of aromatic nitro compounds (4-nitrophenol (4-NP) and 2-nitroaniline (2-NA)) was carried out in the presence of NaBH4. Among the different electrocatalysts (PD-COP, Au@PD-COP-I, Au@PD-COP-II, Au@PD-COP-III and Au@PD-COP-IV) studied in this work, the Au@PD-COP-II demands a low overpotential of 288 mV and 184 mV to attain a 50-mA/cm2 geometrical current density with a lowest Tafel slope value of 56 and 85 mV/dec for OER and HER respectively. From the OER and HER phenomenal activity, a two-electrode system was constructed, and it needs a cell voltage of 1.615 V to conquer a current density of 10 mA/cm2 with outstanding stability for 34 h. The high electroactivity of Au@PD-COP-II may be allied with the presence of innumerable redox-active sites and high electrochemical active surface area (ECSA) towards effective water electrolysis. Further, the catalytic activity performed towards the reduction of 4-NP to 4-aminophenol (4-AP) and 2-NA to o-PDA (o-phenylenediamine), Au@PD-COP-II showed good catalytic activity with a reduction time of 20 and 14 min respectively.

Tailoring the Pore Structure of Porous Ni-Sn Alloys for Boosting Hydrogen Evolution Reaction in Alkali Solution

Ni-based alloy is an ideal candidate for its application in the field of hydrogen evolution of water splitting due to its good durability, excellent catalytic properties and low hydrogen evolution overpotential. In this paper, porous Ni-Sn alloy materials were prepared by activation reaction sintering, and the pore structure was tailored by adjusting Sn content. The effects of Sn content and electrolyte temperature on the hydrogen evolution properties of porous Ni-Sn alloy electrodes in 6 mol·L−1 KOH solution were studied by electrochemical measurement methods, such as cyclic voltammetry (CV) curves, electrochemical impedance spectroscopy (ESI) and linear sweep voltammetry, and the mechanism of hydrogen evolution was further discussed. The experimental results reveal that when Sn content is 45 wt%, porous Ni-Sn alloy exhibits the best catalytic performance for hydrogen evolution with a Tafel slope of 164.69 mV·dec−1 and an overpotential of 170 mV. The tested electrode also shows good stability for hydrogen evolution in alkaline solution, and the apparent activation energy calculated at room temperature is 29.645 kJ·mol−1. The catalytic mechanism of hydrogen evolution is as follows: the addition of Sn significantly reduces the dissociation degree of M-H bonds, thereby reducing the overpotential of hydrogen evolution; with the increase of Sn content, the porous Ni-Sn electrode displays a higher electrochemical active surface area (ECSA), which makes porous Ni-Sn alloy exhibit good hydrogen evolution catalytic performance.

Urea electrooxidation using ZIF-67-derived Co3O4 catalyst

The development of highly efficient and inexpensive electrocatalysts exhibiting long-term stability is essential for energy-related applications. In this work, the Co3O4 catalyst was synthesized by annealing ZIF-67. The as-prepared catalysts were characterized by XRD, XPS, SEM, and TEM. The electro-oxidation activities were measured by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). In urea electro-oxidation (UOR), the ZIF-67-derived Co3O4 catalyst showed a lower Tafel-slope value (134 mV dec−1) than ZIF-67. The Co3O4 electrocatalyst had a higher electrochemical active surface area (ECSA) than ZIF-67, and therefore, it exhibited a higher electrocatalytic performance. CA also revealed that the ZIF-67-derived Co3O4 electrocatalyst exhibited a superior current density than ZIF-67 and exhibited consistent electrocatalytic activity for UOR.

MoSe2 and NiCo2O4/NiO Based HybridNanostructure as Novel Electrocatalyst for High Performance Rechargeable Zinc-Air Battery

Efficient air electrocatalysts are needed to develop eco-friendly rechargeable Zinc-air (Zn-air) batteries for renewable energy storage. Here, we investigate the electrocatalytic activity of hydrothermally synthesized MoSe2, NiCo2O4/NiO and NiCo2O4/NiO-MoSe2 hybrid nanostructure by performing oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) studies. The NiCo2O4/NiO-MoSe2 hybrid nanostructure (Tafel slope∼ 54 mV decade−1) shows best electrocatalytic activity and stability for OER study among synthesized electrocatalysts. Further, the oxygen reduction behaviors of prepared catalysts have been observed in oxygen saturated electrolyte solution. The excellent electrocatalytic activity of hybrid nanostructure can be associated with its high electrochemical active surface area, number of active sites and possibly due to the presence of selenium vacancies and edges in MoSe2. Furthermore, we demonstrate Zn-air batteries with these electrocatalysts as air cathode, showing open circuit potential of 1.42 V, the specific capacity of 1023 mA h gZn−1 and energy density of 1195 W h kgZn−1, with high durability for hybrid nanostructure-based Zn-air battery. To the best of our knowledge, this is the first study demonstrating pristine MoSe2 and NiCo2O4/NiO-MoSe2 hybrid nanostructure-based cathodes for Zn-air batteries with excellent specific capacity and energy density.

Controllable synthesis of urea-assisted Co3O4 nanostructures as an effective catalyst for urea electrooxidation

Nonprecious urea-assisted Co3O4 nanostructures with different urea concentrations were synthesized using a hydrothermal method. The structural variations of four different electrocatalysts of Co3O4 were investigated using X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analyses. The change in morphology of all Co3O4 samples can be ascribed to urea-assisted controlled synthesis procedures. Linear sweep voltammetry, chronoamperometry, and electrochemical impedance spectroscopy studies were conducted using a three-electrode system to examine the electrocatalytic behavior of the samples for the urea oxidation reaction (UOR) in an alkaline medium. Co3O4 synthesized with a high urea concentration exhibited good electrocatalytic activity for the UOR. At an oxidation potential of 0.65 V, the self-assembled electrocatalysts delivered the highest current density of 98.6 mA g−1. This sample showed a higher electrochemical active surface area (ECSA-242.5 mF cm−2) and BET surface area (22.27 m2 g−1) than others. The enhanced electrocatalytic activity of this sample can be attributed to adding a higher urea concentration during the synthesis steps and its structural morphology, which enhanced the reaction kinetics.

Improvement of surface light absorption of ZnO photoanode using a double heterojunction with α–Fe2O3/g–C3N4 composite to enhance photoelectrochemical water splitting

This study investigated a double-heterojunction of a ZnO/α–Fe2O3/g–C3N4 photoanode to overcome each of their intrinsic drawbacks for use as photocatalysts or photoelectrocatalysts ZnO thin film having a wide bandgap and low reduction potential, α–Fe2O3 having insufficient reduction potential, and g–C3N4 having low oxidation potential as photocatalysts. The elemental and chemical mapping of the materials species and free metal ions were investigated for the first-time using time-of-flight–secondary ion mass spectrometry (TOF−SIMS), which is a surface-sensitive analytical method. The depth profile of TOF−SIMS indicated that the α–Fe2O3 and g–C3N4 species were homogeneously covered and chemically connected on the surface of ZnO nanorods. The photoelectrocatalytic (PEC) performance of the ZnO/α–Fe2O3/g–C3N4 photoanode was obtained, and it showed a photocurrent density of 0.97 mA/cm2 at 1.23 VRHE and under 100 mW/cm2 illumination, which was (1.6 and 4.8) fold greater than those of the ZnO/α–Fe2O3 and ZnO photoanode, respectively. The ZnO/α–Fe2O3/g–C3N4 photoanode generated 29.28 μmol/cm2 of H2 and 14.15 μmol/cm2 of O2 at 2 h illumination of 100 mW/cm2 light along with 1.23 VRHE. The inclusion of the dual heterojunction in the ZnO/α–Fe2O3/g–C3N4 photoanode provided lower charge transfer resistance (Rct) and higher electrochemical active surface area (ECSA), which led to simultaneous enhancements in the electron-hole separation and surface light absorption at higher wavelengths, ultimately resulting in substantially improved PEC performance.

Enhanced electro-activity of nickel phosphide by pre-treatment for efficient hydrogen sulfide elimination

Electrochemical sulfide oxidation is a promising approach for sulfide removal from wastewater or biogas due to low energy and chemical consumption. In this work, nickel phosphide was facilely electrodeposited on stainless steel (SS/Ni-P) and comprehensively evaluated as anode catalyst for sulfide oxidation. Electrochemical property analysis suggested that SS/Ni-P had low polarization resistance (109.10 Ω) and high electrochemical active surface area (Cdl = 1.3 mF/cm2). The sulfide removal efficiency of SS/Ni-P achieved 95.00 ± 3.55 % at 1.42 V vs RHE within 48 h, which was 2.60 times and 3.62 times of that by SS/Ni and SS anodes, respectively. The first order kinetic rate constant of SS/Ni-P for sulfide removal was 0.0315 ± 0.0061 h-1, superior than that of the reported single nickel atom based catalyst with stainless steel substrate. Pre-treating SS/Ni-P under a constant external potential for 10 s further improved the electroactivity on sulfide oxidation due to the enhancement of the electrochemical active surface area by 46.56%. Further analysis of the chemical state changes during the sulfide oxidation process revealed that the Ni from Ni-P was the real active center, which formed Ni-S precursors to promote polysulfide formation. This work provided a highly efficient sulfide oxidation anode material for sulfide containing wastewater and biogas treatment.