Half-reaction Research Articles

In-situ photodeposition of cadmium sulfide nanocrystals on manganese dioxide nanorods with rich oxygen vacancies for boosting water-to-oxygen photooxidation

Carrier separation and surface reaction kinetic are two main bottlenecks limiting photocatalytic efficiency of photocatalysts towards an industrial level. In this regard, heterostructures and defects engineering have been proven to be effective strategies for addressing the two issues. However, the integrated construction of heterostructures and defects has been reported rarely. Herein, a facile in-situ photodeposition strategy has been developed to grow CdS nanocrystals on MnO2-x nanorods with rich oxygen vacancies (VO) as a direct Z-scheme photocatalyst for boosting water oxidation. It has been found that the Cd2+ ions accept photoelectrons from MnO2-xunder irradiation for the in-situ growth of CdS nanocrystals, which enables a close contact between the two components, providing high-speed electron-transport channels for photocatalysis. Meanwhile, the photooxidation half reactions extract surface lattice oxygen, leading to the increase of VO content in MnO2-x, which supplies abundant active sites for oxygen evolution. Owing to the synergistic effects of VO and Z-scheme systems, the optimized MnO2-x/CdS photocatalyst displays a dramatically enhanced photocatalytic activity with an O2 production rate of 779 μmol g-1h-1 under visible-light irradiation without any cocatalysts, which is 2.33 times higher than the bare MnO2-x. This work reveals the cooperative manipulation of VO and CdS nanocrystals on MnO2-x for achieving efficient photocatalysis, providing new insights into the construction of high-performance photocatalysts via a combined strategy of Z-scheme heterostructures and surface defects.

Trimetallic nanoplate arrays of Ni-Fe-Mo sulfide on FeNi3 foam: A highly efficient and bifunctional electrocatalyst for overall water splitting

One of the challenges to realize large-scale water splitting is the lack of highly active and low-cost electrocatalysts for its two half reactions: hydrogen and oxygen evolution reactions (HER and OER). In this work, a Mo doping approach is adopted to enhance the HER and OER bifunctionality of NiFe-LDH. The catalyst MoNiFeSx@FeNi3 obtained after sulfidation exhibits further improved catalytic performance and good stability. In KOH solution (1.0 M), ultralow overpotentials of 67 mV and 142 mV work well to reach current densities of 10 mA cm−2 for HER and OER, separately. In urea (0.33 M) and KOH (1.0 M) solutions, catalyst urea oxidation reaction can be significantly promoted by MoNiFeSx@FeNi3, and can reach a current density of 10 mA cm−2 under the condition of 1.31 V. Most importantly, our work elaborates a facile strategy to synthesize novel trimetallic transition metal catalyst as a cut-price substitute for precious metals for highly effective overall water splitting.

Battery-Driven N2 Electrolysis Enabled by High-Entropy Catalysts: From Theoretical Prediction to Prototype Model.

A small-scale standalone device of nitrogen (N2 ) splitting holds great promise for producing ammonia (NH3 ) in a decentralized manner as the compensation or replacement of centralized Haber-Bosch process. However, the design of such a device has been impeded by sluggish kinetics of its half reactions, i.e., cathodic N2 reduction reaction (NRR) and anodic oxygen evolution reaction (OER). Here, it is predicted from density function theory that high-entropy oxides (HEOs) are potential catalysts for promoting NRR and OER, and subsequently develop a facile procedure to synthesize HEOs in the morphology of sea urchin-shaped hollow nanospheres assembled from ultrathin nanosheets. The excellent electrocatalytic activities of HEOs for both NRR (NH3 yield rate: 47.58µg h-1 mg-1 and Faradaic efficiency (FE): 10.74%) and OER (215 mV @10mA cm-2 ) are demonstrated. Consequently, a prototype device of N2 electrolysis driven by commercial batteries is constructed, which can operate smoothly and deliver remarkable NH3 yield rate (41.11µg h-1 mg-1 ) and FE (14.14%). Further mechanism study has attributed the excellent catalytic performances of HEOs to their unique electronic structures originated from multi-metal synergistic effects and entropy increase effects. The work will provide new clues for designing versatile catalysts and devices for large-scale industrialization.

Efficient oxygen evolution reaction on RuO2 nanoparticles decorated onion-like carbon (OLC)

Oxygen evolution reaction (OER) is an important half-cell reaction of the electrical water splitting, for its high overpotential associated with sluggish OER kinetics. Therefore, it is critical to develop highly active and durable electrocatalysts to reduce the overpotential. Herein, ultra-small RuO2 nanoparticles (NPs) supported on onion-like carbon (OLC) and carbon nanotube (CNT) are successfully synthesized by means of wet impregnation combined with annealing treatment, respectively. The microstructure characterization results showed OLC perfect graphitic carbon layer structure, and the RuO2 NPs supported on the OLC possess larger particle size compared with the RuO2 NPs supported on the CNT. Moreover, the electronic structure of Ru in RuO2/OLC was also optimized by the OLC support to be beneficial for the OER. The OER performance of the catalysts were investigated in 1 M KOH solution. The results show RuO2/OLC has a comparable OER activity to the commercial RuO2, but a significantly higher mass activity than the commercial RuO2. When compared with the RuO2/CNT, RuO2/OLC not only exhibits lower overpotential and Tafel slop, but also owns more active sites and higher TOF value, indicating the OLC support improved the OER activity of RuO2/OLC. Moreover, RuO2/OLC showed a superior stability compared with RuO2/CNT, which can be attributed to the excellent electrochemical oxidation-resistance of the OLC.

Progress in Preparation and Research of Water Electrolysis Catalyst for Transition Metal Phosphide

Confronted with growing energy crisis and environmental challenges, water electrolysis for hydrogen production can provide high-density, clean and renewable energy, but limited by sluggish kinetics of two half reaction, anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction(HER). Noble-metal-based electrocatalysts can decrease overpotential and accelerate kinetics dramatically, but limited by its scarcity and high cost. Transitional metal catalysts are abundant, low cost and have potential to become excellent catalyst due to unique electronic structure. Beginning from basic principle of electrocatalysis, this paper focuses on the synthesis method of transitional metal phosphide (TMP), and further discusses modification methods of TMP, including phase tuning, element doping/alloying, interfacial/structural engineering and three-dimensional architecture. Finally, the challenges of TMP are analyzed and future research focuses are prospected.

Layered Double Hydroxides for Oxygen Evolution Reaction towards Efficient Hydrogen Generation

Electrochemical water splitting is one of the effective ways to obtain highly pure hydrogen. However, as one of the two half reactions, oxygen evolution reaction (OER) has a high overpotential, resulting in the low-energy utilization efficiency. Therefore, numerous electrocatalysts have been developed to reduce the energy barrier of OER. Among them, layered double hydroxides (LDHs) are excellent OER electrocatalysts with flexible composition and structure, which have been widely investigated in the past decade. Recent studies have been focusing on the identification of active sites for LDHs during OER process, trying to reveal clear reaction mechanism for designing more efficient LDHs electrocatalysts. Hence, this review tries to discuss the advances in identifying active site of LDHs based OER electrocatalysts for efficient hydrogen generation. We first introduce the effect of structure, composition, and defects to the OER performance of LDHs. Furthermore, main attention is paid on the active sites and mechanisms during OER, especially the coordination structures and catalytic mechanisms of active sites. At the end of this review, we put forward the existing problems and shortcomings in this fields, and propose the corresponding solutions, aiming to further promote the development of outstanding OER electrocatalysts towards efficient hydrogen production.

Recent advances in earth-abundant first-row transition metal (Fe, Co and Ni)-based electrocatalysts for the oxygen evolution reaction

The oxygen evolution reaction (OER) is of fundamental importance as a half reaction and rate-controlling step that plays a predominant function in improving the energy storage and conversion efficiency during the electrochemical water-splitting process. In this review, after briefly introducing the fundamental mechanism of the OER, we systematically summarize the recent research progress for nonprecious-metal-based OER electrocatalysts of representative first-row transition metal (Fe, Co and Ni)-based composite materials. We analyze the effects of the physicochemical properties, including morphologies, structures and compositions, on the integrated performance of these OER electrocatalysts, with the aim of determining the structure-function correlation of the electrocatalysts in the electrochemical reaction process. Furthermore, the prospective development directions of OER electrocatalysts are also illustrated and emphasized. Finally, this mini-review highlights how systematic introductions will accelerate the exploitation of high-efficiency OER electrocatalysts.

Boosting water decomposition by sulfur vacancies for efficient CO2 photoreduction

As the rate-determining half reaction (OER) in the overall CO2 photoreduction, the four-electron-involving OER on S-vacancy sites was favored, therefore facilitating the hole-elimination/proton release and unleashing the CO2 reduction half reaction.

Progress on Platinum-Based Catalyst Layer Materials for H-PEMFC

The constant increase in energy demand and related environmental issues have made fuel cells an attractive technology as an alternative to conventional energy technologies. Like any technology, fuel cells face drawbacks that scientific society has been focused on to improve and optimize the overall technology. Thus, the cost is the main inhibitor for this technology due to the significantly high cost of the materials used in catalyst layers. The current discussion mainly focuses on the fundamental electrochemical half-cell reaction of hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) that are taking place in the catalyst layers consisting of Platinum-based and Platinum-non noble metals. For this purpose, studies from the literature are presented and analyzed by highlighting and comparing the variations on the catalytic activity within the experimental catalyst layers and the conventional ones. Furthermore, an economic analysis of the main platinum group metals (PGMs) such as Platinum, Palladium and Ruthenium is introduced by presenting the economic trends for the last decade.

Electrochemically activated Co-Prussian blue analogue derived amorphous CoB nanostructures: an efficient electrocatalyst for the oxygen evolution reaction.

The oxygen evolution reaction is a kinetically sluggish half-cell reaction which plays an important role in tuning the efficiency of various electrochemical energy conversion systems. However, this process can be facilitated by manipulating the composition and morphology of the electrocatalyst. Here, by tuning the annealing temperature, a series of cobalt borides (CoB@300, CoB@450, CoB@550 and CoB@650) were synthesized from a metal-organic framework Prussian blue analogue (PBA) following boronization. The resulting borides were characterized systematically and we explored their electrocatalytic activity towards the oxygen evolution reaction (OER). In an alkaline electrolyte, the in situ surface transformation of the boride working electrode to the corresponding metaborite and cobalt oxyhydroxide took place which thereafter acted as the active catalytic sites for the OER. Interestingly, the amorphous form of cobalt boride (i.e., CoB@300) shows many fold increased catalytic activity compared to those of crystalline CoB and commercial RuO2 requiring only 290 mV overpotential to reach the benchmarked 10 mA cm-2 current density and the trend follows the order as CoB@300 > CoB@450 > CoB@550 > CoB@650 > PBA. The dominant catalytic activity of the amorphous cobalt boride nanostructure is attributed particularly to its amorphous nature and synergy between the in situ formed catalytically active centres (meta-borites and cobalt oxyhydroxide).

Infrared analysis of catalytic CO2 reduction in hydrogenated germanium.

The oxidation and carbisation kinetics of porous amorphous and nano-crystalline hydrogenated germanium (a-Ge:H and nc-Ge:H) films exposed to ambient air and deionized water have been studied using vibration modes observed by infrared spectroscopy. Based on infrared analysis, a two-step process of first oxidation by water and secondly carbisation by carbon dioxide (CO2) is proposed that partly mimics the (photo-)catalytic processes in artificial (photo)synthesis. It is shown that water acts like the precursor for oxidation of porous a-Ge:H and nc-Ge:H in the first step. The incorporation of oxygen in a-Ge:H and nc-Ge:H alloys occurs preferentially at Ge-dangling bonds and not at the Ge–Ge back bonds like in hydrogenated silicon alloys (next of kin IV-valence element). The formation of germanium oxide (GeO) tissue at void surfaces locally creates Ge alloys with significantly lower energy levels for the valence band that can align with the half reaction for water reduction. The heterogeneous nature of a-Ge:H and nc-Ge:H oxidation will result in local catalytic generation of electrons and protons. It is proposed that these charge carriers and ions act as precursors for the second-step reaction based on carbisation that includes both the adsorption of CO2 and formation of CO and formaldehyde.

Surface Roughening Strategy for Highly Efficient Bifunctional Electrocatalyst: Combination of Atomic Layer Deposition and Anion Exchange Reaction.

Electrocatalytic water splitting, which is an interface-dominated process, can be significantly accelerated by increasing the number of front-line surface active sites (NA ) of the electrocatalyst. In this study, a unique method is used for increasing the NA by converting the smooth ultrathin atomic-layer-deposited nanoshells of the electrocatalysts into nano-roughened active shell layers using a controlled anion-exchange reaction (AER). The coarse thin nanoshells present abundant surface active sites, which are generated owing to the inherent unit-cell volume mismatch induced during the AER. Consequently, the nano-roughened electrodes accelerate the sluggish water reaction kinetics and lower the overpotentials required for the hydrogen and oxygen evolution reactions. In addition, the electronic modulation induced by the nanoshell layer at the core-nanoshell interface amplifies the local electron density, as confirmed using electrochemical analysis data and density functional theory calculations. Because of the integrity of the composite electrodes during water-splitting half-cell reactions, their durability for industrial seawater electrolysis is evaluated. The results indicate that their electrochemical activity does not change significantly after 10 days of continuous overall water splitting.

Mechanism of biotin carboxylase inhibition by ethyl 4-[[2-chloro-5-(phenylcarbamoyl)phenyl]sulphonylamino]benzoate

The rise of antibacterial-resistant bacteria is a major problem in the United States of America and around the world. Millions of patients are infected with antimicrobial resistant bacteria each year. Novel antibacterial agents are needed to combat the growing and present crisis. Acetyl-CoA carboxylase (ACC), the multi-subunit complex which catalyses the first committed step in fatty acid synthesis, is a validated target for antibacterial agents. However, there are at present, no commercially available antibiotics that target ACC. Ethyl 4-[[2-chloro-5-(phenylcarbamoyl)phenyl]sulfonylamino]benzoate (SABA1) is a compound that has been shown to have antibacterial properties against Pseudomonas aeruginosa and Escherichia coli. SABA1 inhibits biotin carboxylase (BC), the enzyme that catalyses the first half reaction of ACC. SABA1 inhibits BC via an atypical mechanism. It binds in the biotin binding site in the presence of ADP. SABA1 represents a potentially new class of antibiotics that can be used to combat the antibacterial resistance crisis.

Bimetallic two-dimensional materials for electrocatalytic oxygen evolution

Electrocatalytic oxygen evolution reaction (OER) is one of the important half reactions of electrocatalytic water splitting. However, the slow kinetic process involving four-electron transfer severely limits its reaction efficiency, which in turn limits the overall electrocatalytic hydrolysis efficiency. In order to improve the activity of the electrocatalytic OER, researchers mainly update the catalyst from three aspects, that is, increase the conductivity of the electrocatalyst, and the quantity and quality of active sites. Two-dimensional (2D) engineering can effectively reduce the resistance of the materials and greatly increase the number of electrochemically active sites, while heterometal doping, or the bimetal strategy, can improve the quality of active sites via changing the electronic structure of the material. Thus, the combination of the two can enhance the activity of electrocatalytic OER in all three aspects: conductivity, number and quality of active sites. However, there is currently no review on this topic. Therefore, in this review, we summarize the application of bimetallic 2D materials in electrocatalytic OER from four aspects: the structure, synthesis strategy, catalytic efficiency, and reaction mechanism.

Ionomer content optimization in nickel-iron-based anodes with and without ceria for anion exchange membrane water electrolysis

Hydrogen production from anion exchange membrane water electrolysis (AEMWE) is an efficient cost-effective solution to renewable energy storage. Contrary to proton exchange membrane (PEM) electrolysis, AEMWE requires further optimization of its cell design, particularly for the kinetically unfavourable oxygen evolution anode half-cell reaction (OER). In this work we optimize the commercial Fumatech fumion ionomer content in AEMWE anodes using nickel (Ni) nanoparticles (NP) synthesized by chemical reduction. The optimal ionomer content is then applied to Ni-iron (Fe)-based NPs with and without ceria (CeO 2 ), all prepared using the same method. Scanning Electron Microscopy (SEM) of the resulting electrode surfaces, Particle-size Distribution (PSD) of the catalyst inks, and in-situ testing of the monometallic Ni NPs show that the best and most active catalytic layer is obtained using 15 wt% ionomer. AEMWE performance and short-term durability are evaluated in different concentrations of potassium hydroxide (KOH), where the Ni 90 Fe 10 is the best performing Ni-based electrode showing 1.72 V at 0.8 A cm −2 in 1 M KOH after IR-correction, and a degradation rate of 3.3 mV h −1 . The addition of ceria to the Ni-based catalysts shows more consistent mass transfer over time likely due to more efficient water transport and bubble release. • 15 wt% Fumion is required for high AEMWE performance of NiFe/CeO 2 nanoparticles. • Ni 90 Fe 10 shows a cell voltage of 1.72 V at 0.8 A cm −2 in 1 M KOH. • Ni 80 Fe 20 /10 wt% CeO 2 shows a cell voltage of 1.67 V at 0.4 A cm −2 in 0.1 M KOH. • Ni 90 Fe 10 shows the best stability of the Ni-based materials over 12 h at 0.5 A cm −2 • CeO 2 can help improve charge transfer as well as mass transfer over time.

Preparation of CdS@TiO2/Ni2P photocatalyst for value-added organic transformation coupling with enhanced hydrogen evolution

In a dual-functional photocatalytic reaction system with coupled selective organic reductions and oxidation reaction, both the photogenerated electrons and holes can be simultaneously utilized to generate value-added products, make the overall process more valuable from a sustainability and economic perspective. Herein, CdS&P25–Ni 2 P (SPN) has been synthesized, which realized the selective transformation of organic compounds coupled with hydrogen evolution under visible light condition. The traditional sacrificial agent oxidation reaction is replaced by the dehydrogenation half reaction of aromatic alcohol with higher additional value, where high efficiency photocatalytic reaction can be realized. The effects of solvent, substituents, component of photocatalyst, co-catalyst loading and other factors on this reaction were explored. Under the optimal conditions, the substrate was almost completely transformed within 5 ​h, and the hydrogen production rate can reach 1.148 ​mmol·g cat −1 ·h −1 . Through compare the research of different reaction systems, different possible reaction mechanisms and reaction paths have been proposed. This paper further explores the field of organic value-added transformation coupled with hydrogen production and provides a new strategy for the effective use of photogenerated electrons and holes, which will be inspirational for the future involving catalysis, materials and other fields.

Recent Progress on Transition Metal Based Layered Double Hydroxides Tailored for Oxygen Electrode Reactions

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), namely, so-called oxygen electrode reactions, are two fundamental half-cell reactions in the energy storage and conversion devices, e.g., zinc–air batteries and fuel cells. However, the oxygen electrode reactions suffer from sluggish kinetics, large overpotential and complicated reaction paths, and thus require efficient and stable electrocatalysts. Transition-metal-based layered double hydroxides (LDHs) and their derivatives have displayed excellent catalytic performance, suggesting a major contribution to accelerate electrochemical reactions. The rational regulation of electronic structure, defects, and coordination environment of active sites via various functionalized strategies, including tuning the chemical composition, structural architecture, and topotactic transformation process of LDHs precursors, has a great influence on the resulting electrocatalytic behavior. In addition, an in-depth understanding of the structural performance and chemical-composition-performance relationships of LDHs-based electrocatalysts can promote further rational design and optimization of high-performance electrocatalysts. Finally, prospects for the design of efficient and stable LDHs-based materials, for mass-production and large-scale application in practice, are discussed.

Efficient photocatalytic H2-evolution coupled with valuable furfural-production on exquisite 2D/2D LaVO4/g-C3N4 heterostructure

Effectively utilize photogenerated holes (h+) of catalysts while blocking rapid recombination of photoinduced carriers are the two critical challenges for solar-to-hydrogen (STH) conversion. Here, an exquisite 2D/2D LaVO4/g-C3N4 (LaVO4/CN) heterostructure is delicately designed and fabricated for efficient photocatalytic H2-evolution while producing high value-added furfural simultaneously. The abundant biomass furfuryl alcohol (FFA) is employed to substitute the traditional h+ sacrificial agents such as triethanolamine (TEOA) for the oxidation half reaction, which is very meaningful to balance the H2-evolution half reaction. The LaVO4/CN heterojunction enables 3-time increased H2-evolution and a high furfural-production rate (0.95 mmol g−1 h−1) than that of pristine graphite carbon nitride (g-C3N4, labeled as CN), and with a 22.16% H2-evolution apparent quantum efficiency (AQE) irradiated at 400 nm. This work provides an exquisite catalyst and a new strategy for efficient photocatalytic H2-evolution coupled with production of high valuable chemicals.

Improving the Stability of Protein-Protein Interaction Assay FlimPIA Using a Thermostabilized Firefly Luciferase.

The protein–protein interaction assay is a key technology in various fields, being applicable in drug screening as well as in diagnosis and inspection, wherein the stability of assays is important. In a previous study, we developed a unique protein–protein interaction assay “FlimPIA” based on the functional complementation of mutant firefly luciferases (Fluc). The catalytic step of Fluc was divided into two half steps: D-luciferin was adenylated in the first step, while adenylated luciferin was oxidized in the second step. We constructed two mutants of Fluc from Photinus pyralis (Ppy); one mutant named Donor is defective in the second half reaction, while the other mutant named Acceptor exhibited low activity in the first half reaction. To date, Ppy has been used in the system; however, its thermostability is low. In this study, to improve the stability of the system, we applied Fluc from thermostabilized Luciola lateralis to FlimPIA. We screened suitable mutants as probes for FlimPIA and obtained Acceptor and Donor candidates. We detected the interaction of FKBP12-FRB with FlimPIA using these candidates. Furthermore, after the incubation of the probes at 37°C for 1 h, the luminescence signal of the new system was 2.4-fold higher than that of the previous system, showing significant improvement in the stability of the assay.

The Restructuring-Induced CoO x Catalyst for Electrochemical Water Splitting.

Restructuring is an important yet less understood phenomenon in the catalysis community. Recent studies have shown that a group of transition metal sulfide catalysts can completely or partially restructure during electrochemical reactions which then exhibit high activity even better than the best commercial standards. However, such restructuring processes and the final structures of the new catalysts are elusive, mainly due to the difficulty from the reaction-induced changes that cannot be captured by ex situ characterizations. To establish the true structure–property relationship in these in situ generated catalysts, we use multimodel operando characterizations including Raman spectroscopy, X-ray absorption spectroscopy, and X-ray reflectivity to investigate the restructuring of a representative catalyst, Co9S8, that shows better activity compared to the commercial standard RuO2 during the oxygen evolution reaction (OER), a key half reaction in water-splitting for hydrogen generation. We find that Co9S8 ultimately converts to oxide cluster (CoOx) containing six oxygen coordinated Co octahedra as the basic unit which is the true catalytic center to promote high OER activity. The density functional theory calculations verify the in situ generated CoOx consisting of edge-sharing CoO6 octahedral clusters as the actual active sites. Our results also provide insights to design other transition-metal-based materials as efficient electrocatalysts that experience a similar restructuring in OER.