H2 Evolution Reaction Research Articles

Construction of Co9Se8/TiO2 S‐scheme heterojunction photocatalyst for efficient hydrogen production

Construction of S-scheme heterostructure is the focus of catalyst modification in the field of photocatalysis. In this work, the nanosized Co9Se8 and TiO2 particles were fabricated via a simple hydrothermal process. A series of Co9Se8/TiO2 heterojunctions were subsequently constructed through a physical solvent evaporation strategy. The photocatalytic H2 evolution experiment shows that the H2 evolution rate can reach 8282.7 μmol·g−1·h−1 over 15 %-Co9Se8/TiO2 under 300 W Xe lamp irradiation using 20 % triethanolamine (TEOA) as the sacrifice agent, which is 29.9-fold and 95.8-fold higher than that of pristine TiO2 (277.3 μmol·g−1·h−1) and Co9Se8 (86.5 μmol·g−1·h−1), respectively. The enhanced photocatalytic performance is primarily attributed to the improved light absorption ability and the formed S-scheme heterojunctions between TiO2 and Co9Se8, which could efficiently accelerate the separation and migration of photo-induced charges. Furthermore, the powerful electrons and holes are preserved, thereby earned robust redox ability to prompt H2 evolution reaction. This work affords a feasible approach to obtain S-scheme photocatalysts for effectively converting solar energy to H2.

A Universal Descriptor in Determining H2 Evolution Activity for Dilute Aqueous Zn Batteries

AbstractLarge‐scale energy storage with aqueous Zn batteries (AZBs) have bright future, but their practical application is impeded by H2 evolution reaction (HER), which results in poor stability of Zn–metal anodes. Here, using linear sweep voltammetry in dilute salt aqueous electrolytes, it is discovered that as the salt concentration decreases, HER is gradually suppressed, which is contrary to prior beliefs. Combining calculations and experiments, it is demonstrated that HER derives predominantly from the sum of Zn2+‐solvated water rather than the average amount of water in the Zn2+‐solvation structural unit or free water without interaction with Zn2+, which answers the puzzle from above. This result, which differs fundamentally from the previous understandings, sheds new light on the mysterious role of water chemistry in controlling HER and contributes to a more rational design of advanced electrolytes for AZBs.

Activation of 2D cobalt hydroxide with 0D cobalt oxide decoration for microplastics degradation and hydrogen evolution

The 2D semiconductors are important players in environmental and energy fields due to their unique catalytic and physical properties defined by their dimensionality. Versatile functionalities on one 2D matrix will enlarge its application scopes but require dedicated engineering paths. In this work, we present a cross-dimensional strategy by decorating 0D Co3O4 onto 2D Co(OH)2 to form a multifunctional photocatalyst. The one-pot hydrothermally synthesized Co3O4@Co(OH)2 composite is capable of degrading polystyrene microplastics with an efficiency of 40% under 0.495 W white LED illumination. In a separated experiment, H2 evolution reaction from water splitting was evaluated in absence of sacrificial agents leading to 43 μmol g−1 and to an apparent quantum efficiency of 3.48% at 420 nm. The study of the energy band diagrams by UV–Visible and ambient photoemission spectroscopy and the analysis of the radicals involved in the reaction of photocatalytic degradation allow to unveil the mechanisms for both the processes herein studied. Finally, we could confirm that the heterostructure benefits the redox potentials of 2D and 0D counterparts and facile electron transfers when crossing two different dimensions. These results provide guidelines and inspiration for cross-dimensional activations of low-dimensional materials for versatile functionalities.

Ag-Doped WO3 Nanoplates as Heterogenous Multifunctional Catalyst for Glycerol Acetylation, Electrocatalytic and Enhanced Photocatalytic Hydrogen Production.

Herein, we report a hydrothermal method to synthesize pristine and Ag-doped WO3 nanoplates and study their multifunctional competence in the accomplishment of enhanced catalytic organic conversion and highly efficient photocatalytic and electrocatalytic H2 evolution reactions. The as-synthesized nanoplates were characterized by using various techniques including X-ray diffraction, field emission scanning electron microscopy-energy-dispersive X-ray analysis, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and BET surface area studies. The significant catalytic performance was shown by 1% Ag-doped WO3 nanoplates with 100% glycerol conversion and 90% triacetin selectivity. The photocatalytic activity was also examined toward water splitting H2 evolution reaction which demonstrates the highest H2 evolution of 12.06 mmol g-1 catalyst for 1% Ag-doped WO3 nanoplates in a time span of 8 h. Moreover, the electrocatalytic hydrogen evolution reaction was also monitored in acidic media (0.1 M H2SO4) which demonstrates good results for 1% Ag-doped WO3 nanoplates with a low overpotential of 0.53 V and a low Tafel slope of 40 mV dec-1.

Strongly coupled NH2NH-modified high crystallinity Graphene quantum dots/Carbon Nitride for efficient photocatalytic hydrogen evolution

For the application of photocatalysis, the development of noble metal-free cocatalysts is crucial. Here, a simple molecular fusion method was employed to create high crystallinity GQDs with the –NHNH2 modification, which were then used as an effective metal-free cocatalyst in the photocatalytic H2 evolution reaction. The modified –NHNH2 Lewis base active sites, the quick charge separation channels, and the improved electric conductivity allowed the optimized NHNH2-GQDs/PUCN sample to exhibit an H2 evolution rate of 204.2 μmol g−1 h−1, which is an 80-fold greater activity than that of pure PUCN. This work will provide insights into the design of metal-free cocatalysts for photocatalytic H2 evolution applications.

Degradation of Chloroform by Zerovalent Iron: Effects of Mechanochemical Sulfidation and Nitridation on the Kinetics and Mechanism.

Chloroform (CF) is a widely used chemical reagent and disinfectant and a probable human carcinogen. The extensive literature on halocarbon reduction with zerovalent iron (ZVI) shows that transformation of CF is slow, even with nano, bimetallic, sulfidated, and other modified forms of ZVI. In this study, an alternative method of ZVI modification─involving simultaneous sulfidation and nitridation through mechanochemical ball milling─was developed and shown to give improved degradation of CF (i.e., higher degradation rate and inhibited H2 evolution reaction). The composite material (denoted as S-N(C)-ZVI) gave synergistic effects of nitridation and sulfidation on CF degradation. A complete chemical reaction network (CRN) analysis of CF degradation suggests that O-nucleophile-mediated transformation pathways may be the main route for the formation of the terminal nonchlorinated products (formate, CO, and glycolic polymers) that have been used to explain the undetected products needed for mass balance. Material characterizations of the ZVI recovered after batch experiments showed that sulfidation and nitridation promoted the formation of Fe3O4 on the S-N(C)-ZVI particles, and the effect of aging on CF degradation rates was minor for S-N(C)-ZVI. The synergistic benefits of sulfidation and nitridation on CF degradation were also observed in experiments performed with groundwater.

Electrolessly Deposited Carbon-Supported CuNiSn Electrocatalysts for the Electrochemical Reduction of CO2

Aiming at developing low-cost, high-performance catalysts for the electrochemical reduction of CO2 (CO2-ERR) to valuable multicarbon (C2–C3) chemicals to alleviate global warming, trimetallic alloy electrocatalysts containing Cu, Ni, and Sn supported on a Pd-activated carbon fabric substrate (CS) were prepared via an electroless deposition method. The as-deposited CuNiSn/CS electrocatalysts were employed in CO2-ERR in an H-cell type reactor at an applied potential of −1.6 V vs. Ag/AgCl. The effect of the electroless deposition time (15, 30, and 45 min) was investigated, finding no significant structural differences according to the X-ray diffraction patterns. The evaluation of the reaction performance via linear sweep voltammetry revealed that CO2 was more effectively reduced to adsorbed species on the catalytic surface sites of the electrocatalyst prepared with a 30 min deposition time. The analysis of the gas and liquid products via gas chromatography and nuclear magnetic resonance, respectively, revealed that the Faradaic efficiency and H2 production over CuNiSn/CS was lower than those over related bimetallic and monometallic electrocatalysts, indicating the inhibition of the competitive H2 evolution reaction. Liquid products including formate, ethylene glycol, acetone, ethanol, acetate, and 1-buthanol were detected.

Boosting electrochemical CO2 reduction via valence state and oxygen vacancy controllable Bi–Sn/CeO2 nanorod

Electrocatalytic CO2 reduction reaction (CO2RR) to produce formate has been recognized as one of the most efficient strategies to convert CO2 to energy-rich products and store renewable energy compared with other methods such as biological reduction, thermal catalytic reduction, and photocatalytic reduction. Developing an efficient catalyst is crucial to enhance the formate Faradaic efficiency (FEformate) and retard the competing H2 evolution reaction. The combination of Sn and Bi has been demonstrated to be effective in inhibiting the evolution of H2 and the generation of CO, promoting the formation of formate. Herein, we design Bi- and Sn-anchored CeO2 nanorods catalysts with the valence state and oxygen vacancy (Vo) concentration controllable for CO2RR by reduction treatment at different environments. The m-Bi1Sn2Ox/CeO2 with moderate H2 composition reduction and suitable Sn/Bi molar ratio achieves a remarkable FEformate of 87.7% at −1.18 V vs. RHE compared with other catalysts. Additionally, the selectivity of formate was maintained over 20 h with an outstanding FEformate of above 80% in 0.5 M KHCO3 electrolyte. The outstanding CO2RR performance was attributed to the highest surface Sn2+ concentration which improves the formate selectivity. Further, the electron delocalization effect between Bi, Sn, and CeO2 tunes electronic structure and Vo concentration, promoting the CO2 adsorption and activation as well as facilitating the formation of key intermediates HCOO* as evidenced by the in-situ Attenuated Total Reflectance-Fourier Transform Infrared measurements and Density Functional Theory calculations. This work provides an interesting measure for the rational design of efficient CO2RR catalysts via valence state and Vo concentration control.

Triggering the electrocatalytic performance of MoS2 nanosheets via the synergy of doping with W and supporting on montmorillonite

Benefiting from the two-dimensional structure, edge active sites, and rich resources, MoS2 has attracted increasing attention as a potentially efficient electrocatalyst for the H2 evolution reaction (HER). However, its electrocatalytic property is currently restricted by the poor reactivity and exposure of active sites. Doping with heteroatom and supporting on the matrix are two effective strategies to enhance the electrocatalytic H2 evolution. Herein, the electrocatalytic performance of MoS2 nanosheets was triggered via the synergy of doping with W and supporting on montmorillonite (Mt). The dual two-dimensional composites of W-doped MoS2 nanosheets supported on Mt were fabricated via a one-step hydrothermal method. The synergistic effect of doping with W and supporting on Mt results in the nano heterostructure, high electrocatalytic property for the HER, low Tafel slope (60 mV/decade) and excellent catalytic stability. Doping with W could facilitate the reactivity of catalytic active sites, while supporting on Mt could promote active site exposure and the hydrophilicity of MoS2 nanosheets. The strategy in this study provides a promising path to efficiently enhance the catalytic performances of MoS2 composite electrocatalysts.

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

Respirometric in Situ Methods for Real-Time Monitoring of Corrosion Rates: Part III. Deconvolution of Electrochemical Polarization Curves

A highly sensitive respirometric method is presented that allows real-time monitoring of reaction rates involving H2 and O2 during electrochemical polarization. The measurement approach is based on simultaneous monitoring of the changes in the total pressure and the O2 partial pressure inside a closed chamber. Hence, it is possible to quantify the rates resulting from reactions such as HER, ORR and OER as a function of the applied potential. As a result, deconvolution of the net electric current into cathodic and anodic partial reaction rates during electrochemical polarization can be obtained. It was demonstrated that the respirometric monitoring approach can reveal superfluous cathodic reactions from Al during cathodic polarization as well as during anodic polarization of Al and Mg AZ31. Thus, the true metal oxidation rate could be determined from the electric current and the cathodic reaction rates. Furthermore, the rate of the HER during cathodic electrodeposition of Zn was measured. Through respirometric monitoring of Ni and stainless steel at high anodic potentials, the rate of O2 evolution could be distinguished from electrode oxidation processes.

Porphyrin conjugated polymer/Pt-loaded graphite carbon nitride nanocomposites for efficient charge separation and broadband responsive H2 evolution

An efficient broadband responsive two-dimensional (2D) heterometallic Zn-/Co-porphyrin conjugated polymer (ZnCoP-F CP) with its Co-porphyrin bridging unit bearing two perfluorophenyls is coupled with 2.0 wt% Pt-loaded graphite carbon nitride (PCN) to fabricate a novel 2D/2D nanocomposite (ZnCoP-F/PCN). The resultant ZnCoP-F/PCN composite with an optimal mass ratio exhibits broadband (UV–vis–NIR) responsive H2 evolution reaction (HER) activity up to 432 μmol h−1, 5.2 and 2.8 times higher than that of the ZnCoP-F CP (83 μmol h−1) and PCN (151 μmol h−1) alone, respectively. Furthermore, the ZnCoP-F/PCN displays excellent apparent quantum yields (AQY) of 18.2%, 18.3%, 17.6%, 16.5%, 13.9%, 8.7%, 5.1%, 4.3%, 1.9%, 0.95% and 0.62% at 350, 380, 420, 450, 500, 550, 600, 700, 785, 850 and 950 nm, which are also higher than that of ZnCoP-F CP illuminated at the respective monochromatic light. The enhanced broadband responsive HER performance of ZnCoP-F/PCN can be attributed to the easily assembled ZnCoP-F CP and PCN nanosheets through strong π–π stacking interaction, which can facilitate the fast charge transfer from ZnCoP-F CP to PCN for HER. This work opens a new pathway to fabricate porphyrin polymer-based nanocomposite for more efficiently converting solar radiation and water into H2.

Free-Standing Dendritic Nanostructured Co/CNT/Carbon Nanofiber Composites for Efficient Water Splitting in Alkaline Media

Exploring highly efficient three-dimensional (3D) nanoarchitectures for H2 and O2 evolution reaction (HER and OER) has received tremendous interest. Here, a binder-free free-standing cobalt/bamboo-shaped carbon nanotube/carbon nanofiber (Co/CNT/CNF) film was prepared based on electrospinning, followed by thermal treatment. The synergistic effect between Co cores, CNT shells (5 nm), and CNF skeletons endows the as-prepared Co/CNT/CNF with a 3D porous dendritic nanostructure. Therefore, the unique Co/CNT/CNF film demonstrates prominent HER (overpotential = 129 mV) and OER (overpotential = 162 mV) catalysis behavior at 10 mA cm–2. Meanwhile, the as-prepared Co/CNT/CNF film displays excellent overall water splitting activity as well as durability (at least 40 h both under 10 and 40 mA cm–2). Moreover, the facile electrospinning followed by the thermal treatment approach is economically practical for flexible film production, which has great potential for industrial application in water splitting technology.

ZnxZrO2+x-Based Photocatalyst with Dual Active Sites for Tunable Syngas Production from CO2 Photoreduction

Photocatalytic reduction of CO2 in H2O to CO and H2 for syngas production is an attractive option to solve global warming and generate a feedstock for the Fischer–Tropsch process. The syngas generated from CO2 photoreduction with a precise and controllable ratio of H2/CO remains a major challenge to date. In this work, CdS-sensitized nanoscale ZnxZrO2+x solid solutions with dual active sites were synthesized as photocatalysts for tunable syngas H2 and CO production from CO2 photoreduction. The staggered band energy alignments, electron paramagnetic resonance results, and the site of palladium/gold nanoparticles by photodeposition indicate that the charge transfer in the CdS/ZnxZrO2+x heterojunction mainly follows the conventional type II mechanism. Density functional theoretical calculation results reveal that Zn and Zr sites on ZnxZrO2+x are favorable for the adsorption of H2O and CO2 molecules and generation of H2 and CO, respectively. The H2/CO ratio can be controlled in the range from 0.9 to 25.0 by adjusting the content of Zn in ZnxZrO2+x. Moreover, syngas production can be further improved by the modification of Pd nanoparticles. For the first time, this work proposes a strategy to construct a photocatalyst with dual active sites for effectively controlling the H2/CO ratio in syngas synthesis through a fundamental understanding of adsorption and catalytic reaction sites in both H2 evolution and CO2 reduction reactions.

A Stable Triphenylamine-Based Zn(II)-MOF for Photocatalytic H2 Evolution and Photooxidative Carbon–Carbon Coupling Reaction

Efficient charge transfer has always been a challenge in heterogeneous MOF-based photoredox catalysis due to the poor electrical conductivity of the MOF photocatalyst, the toilless electron-hole recombination, and the uncontrollable host-guest interactions. Herein, a propeller-like tris(3'-carboxybiphenyl)amine (H3TCBA) ligand was synthesized to fabricate a 3D Zn3O cluster-based Zn(II)-MOF photocatalyst, Zn3(TCBA)2(μ3-H2O)H2O (Zn-TCBA), which was applied to efficient photoreductive H2 evolution and photooxidative aerobic cross-dehydrogenation coupling reactions of N-aryl-tetrahydroisoquinolines and nitromethane. In Zn-TCBA, the ingenious introduction of the meta-position benzene carboxylates on the triphenylamine motif not only promotes Zn-TCBA to exhibit a broad visible-light absorption with a maximum absorption edge of 480 nm but also causes special phenyl plane twists with dihedral angles of 27.8-45.8° through the coordination to Zn nodes. The semiconductor-like Zn clusters and the twisted TCBA3- antenna with multidimensional π interaction sites facilitate photoinduced electron transfer to render Zn-TCBA a good photocatalytic H2 evolution efficiency of 27.104 mmol·g-1·h-1 in the presence of [Co(bpy)3]Cl2 under visible-light illumination, surpassing many non-noble-metal MOF systems. Moreover, the positive enough excited-state potential of 2.03 V and the semiconductor-like characteristics of Zn-TCBA endow Zn-TCBA with double oxygen activation ability for photocatalytic oxidation of N-aryl-tetrahydroisoquinoline substrates with a yield up to 98.7% over 6 h. The durability of Zn-TCBA and the possible catalytic mechanisms were also investigated by a series of experiments including PXRD, IR, EPR, and fluorescence analyses.

Fabrication of MnO2/g-C3N4 hetero-junction for hydrogen production and rhodamine B/methylene blue dye degradation

Over the past few decades, significant progress has been made in the area of clean and renewable energy resources to cope with the rapid diminish of fossil fuels. To suffice this purpose, photocataytic hydrogen production using heterojunctions is drawing a lot of attention. For this purpose a MnO2/g-C3N4 heterojunctions has been fabricated using hydrothermal method. The fabricated sample has been characterized by PXRD, SEM and EDX analysis. The XPS analysis reveals about the presence of Mn, C, N and O elements in the sample. The bandgap for MnO2/g-C3N4 narrowed to 1.75 eV, favouring the harvesting of visible-light. In the photocatalytic H2 evolution reaction (HER), MnO2/g-C3N4 heterojuctions exhibited promising results with 3855 μmol g−1 H2 production via Z-scheme mechanism, where e− produced in MnO2 are accumulated in the valance band of g-C3N4, increasing the lifetime of generated e− and h+. Fabricated MnO2/g-C3N4 heterojunctions have also been used for degradation of industrial dye viz. Rhodamine B (RhB) and Methyl orange (MO).

Activities in photocatalytic hydrogen evolution of In2O3/In2S3 heterostructure and In2O3/In2S3@PAN nanofibers

Fabrication of flexible photocatalysts with the heterostructure is one of promising approaches to improve the photocatalytic activity and reusability. In the present work, the In2O3/In2S3 heterostructures were synthesized by the solvothermal reactions. And the In2O3/In2S3@PAN nanofibers were synthesized by loading In2O3/In2S3 nanoparticles on the surface of PAN nanofibers. The SEM, TEM and elemental mapping images exhibit the homogeneous distribution of the In2O3/In2S3 nanoparticles over the whole surface of nanofibers. The increased photocurrent density and decreased radius of EIS curve indicate that higher effective separation for photogenerated electron-hole pairs and charge transfer were obtained by the In2O3/In2S3 heterostructures. The loading on the surface of PAN nanofibers gives a larger number of photoactive sites to the H2 evolution reactions. And the H2 evolution rate in the photocatalytic process with the presence of the In2O3/In2S3-3@PAN photocatalyst is ∼10.32 and ∼5.33 times higher than the rates of pure In2O3 and In2S3.

Sulfur vacancy MoS2 for electrocatalytic reduction of nitrate to ammonia with enhanced selectivity

As an important raw material, ammonia consumes a significant amount of the world’s energy. The electrocatalytic reduction of nitrate to ammonia provides a new way to generate NH3 from waste water under benign conditions. However, NO3− conversion toward N2 and H2 evolution reaction (HER) competition limit the development of nitrate reduction to ammonia. In this study, we synthesized MoS2 with sulfur vacancies (SVs) using a one-step hydrothermal method, and we used the SVs to utilize the H* from the side reaction HER and accelerate the process of *N to NH3. MoS2 with SVs exhibits higher ammonia synthesis performance and faradaic efficiency (FE) than that of MoS2, with ammonia yield enhancing from 76.67 μg h−1 mgcat.−1 to 111.33 μg h−1 mgcat.−1 and FE expanding from 44.62 % to 78.04 % at − 0.6 V vs. RHE at ambient conditions. Calculations using density functional theory discovered that the presence of SVs effectively lowered the energy barrier in the potential-determining step for nitrate reduction, and H* couples with nearby *N at Mo sites promote activity. This research enhances our knowledge of how to handle the content of MoS2 with SVs when preparing monolayered MoS2 with special catalytic properties.

Electrified hydrocarbon-to-oxygenates coupled to hydrogen evolution for efficient greenhouse gas mitigation

Chemicals manufacture is among the top greenhouse gas contributors. More than half of the associated emissions are attributable to the sum of ammonia plus oxygenates such as methanol, ethylene glycol and terephthalic acid. Here we explore the impact of electrolyzer systems that couple electrically-powered anodic hydrocarbon-to-oxygenate conversion with cathodic H2 evolution reaction from water. We find that, once anodic hydrocarbon-to-oxygenate conversion is developed with high selectivities, greenhouse gas emissions associated with fossil-based NH3 and oxygenates manufacture can be reduced by up to 88%. We report that low-carbon electricity is not mandatory to enable a net reduction in greenhouse gas emissions: global chemical industry emissions can be reduced by up to 39% even with electricity having the carbon footprint per MWh available in the United States or China today. We conclude with considerations and recommendations for researchers who wish to embark on this research direction.

Highly dispersed PtO over g-C3N4 by specific metal-support interactions and optimally distributed Pt species to enhance hydrogen evolution rate of Pt/g-C3N4 photocatalysts

Understanding the fundamental chemistry of metal-support interactions during catalyst preparation is essential to develop a highly efficient Pt/g-C3N4 photocatalyst for the H2 evolution reaction (HER). In this study, we prepared Pt/g-C3N4 photocatalysts via a loading process of different Pt contents onto solvothermally treated g-C3N4 (SCN) and a successive hydrogen reduction. The physicochemical interactions between Pt species and O-containing functional groups over SCN were tracked, and we investigated how the interactions influenced the photocatalytic properties and performance of Pt/SCN. During the reduction process, Pt(OH)22+ ions in liquid phase specifically interacted with neighboring C = O groups over SCN, resulting in highly dispersed PtO species via chemical bonding to SCN. Due to the limited number of the neighboring C = O groups over SCN, the chemically bonded PtO species were saturated at a certain amount, and 1Pt/SCN (1 wt% of Pt) showed the highest Pt dispersion in this study. In the reduction process, excess Pt was readily reduced to Pt metallic phase and then agglomerated in Pt clusters at high Pt loadings. Therefore, the highly active and stable Pt2+ sites were uniformly dispersed and immobilized over 1Pt/SCN by specific interactions with the O-containing functional groups, showing an outstanding HER activity per gram Pt (120.6 mmol∙gPt−1∙h−1). However, data for the optical and electrochemical properties demonstrated that 3Pt/SCN (3 wt% of Pt) had the best charge separation efficiency because of the optimal distribution of the Pt species over SCN. Correspondingly, the optimized 3Pt/SCN exhibited the highest HER rate of 1255.52 μmol∙gcat−1∙h−1, which was about 50 times higher than SCN photocatalyst (25.2 μmol∙gcat−1∙h−1).