Efficient H2 Evolution Research Articles

In situ synthesis of Cu‐doped ZIF‐8 for efficient photocatalytic water splitting

Metal–organic frameworks (MOFs) reached a new level of research in photocatalysis by their virtue of tunable structure, modifiable pores, and a large surface area. Herein, we employed a simple metal ion exchange method to change ZIF‐8 from UV light to visible light absorption photocatalyst. In this work, Cu2+ ions are integrated within the ZIF‐8 framework to synthesize Cu‐doped ZIF‐8 photocatalysts and well characterized by using both the spectroscopic and electrochemical studies. The Cu@ZIF‐8 (CDZ‐20) photocatalyst shows enhanced light‐harvesting ability and remarkable hydrogen generation rate of 13.9 mmolg−1 h−1 with an apparent quantum efficiency (AQE) of 9.08%, which is 17 times higher than that of pristine ZIF‐8 photocatalyst. The higher photocurrent density of 34 μA/cm2 in CDZ‐20 further reinforced the superiority over the ZIF‐8 (1 μA/cm2). This work paves the way to engineer robust copper doped ZIFs photocatalyst under mild synthesis approach for efficient H2 evolution.

Atomically Dispersed MoOx on Rhodium Metallene Boosts Electrocatalyzed Alkaline Hydrogen Evolution

AbstractAccelerating slow water dissociation kinetics is key to boosting the hydrogen evolution reaction (HER) in alkaline media. We report the synthesis of atomically dispersed MoOx species anchored on Rh metallene using a one‐pot solvothermal method. The resulting structures expose the oxide‐metal interfaces to the maximum extent. This leads to a MoOx‐Rh catalyst with ultrahigh alkaline HER activity. We obtained a mass activity of 2.32 A mgRh−1 at an overpotential of 50 mV, which is 11.8 times higher than that of commercial Pt/C and surpasses the previously reported Rh‐based electrocatalysts. First‐principles calculations demonstrate that the interface between MoOx and Rh is the active center for alkaline HER. The MoOx sites preferentially adsorb and dissociate water molecules, and adjacent Rh sites adsorb the generated atomic hydrogen for efficient H2 evolution. Our findings illustrate the potential of atomic interface engineering strategies in electrocatalysis.

Atomically Dispersed MoOx on Rhodium Metallene Boosts Electrocatalyzed Alkaline Hydrogen Evolution.

Accelerating slow water dissociation kinetics is key to boosting the hydrogen evolution reaction (HER) in alkaline media. We report the synthesis of atomically dispersed MoOx species anchored on Rh metallene using a one-pot solvothermal method. The resulting structures expose the oxide-metal interfaces to the maximum extent. This leads to a MoOx -Rh catalyst with ultrahigh alkaline HER activity. We obtained a mass activity of 2.32 A mgRh -1 at an overpotential of 50 mV, which is 11.8 times higher than that of commercial Pt/C and surpasses the previously reported Rh-based electrocatalysts. First-principles calculations demonstrate that the interface between MoOx and Rh is the active center for alkaline HER. The MoOx sites preferentially adsorb and dissociate water molecules, and adjacent Rh sites adsorb the generated atomic hydrogen for efficient H2 evolution. Our findings illustrate the potential of atomic interface engineering strategies in electrocatalysis.

On the influence of hydrothermal treatment pH on the performance of Bi2WO6 as photocatalyst in the glycerol photoreforming.

Solar driven semiconductor-based photoreforming of biomass derivatives, such as glycerol is a sustainable alternative towards green hydrogen evolution concerted with production of chemical feedstocks. In this work, we have investigated the influence of the pH of the hydrothermal treatment on the efficiency of Bi2WO6 as photocatalyst in the glycerol photoreforming. Bi2WO6 is pointed as a promising material for this application due its adequate band gap and the ability to promote hole transfer directly to glycerol without formation of non-selective ⋅OH radicals. Samples prepared at neutral to moderate alkaline conditions (pH = 7-9) are highly crystalline, while those prepared in acidic media (pH = 0-2) exhibit higher concentrations of oxygen vacancies. At pH = 13, the non-stoichiometric Bi(III)-rich phase Bi3.84W0.16O6.24 is formed. All samples were fully characterized towards their optical and morphological properties. UV-Vis irradiation of the photocatalysts modified with 1% m/m Pt and in the presence of 5% v/v aqueous glycerol solution leads to H2 evolution and glycerol oxidation. The sample prepared at pH = 0 exhibited the highest photonic efficiency (ξ) for H2 evolution (1.4 ± 0.1%) among the investigated samples with 99% selectivity for simultaneous formic acid formation. Similar performance was observed for the non-stoichiometric Bi3.84W0.16O6.24 sample (ξ = 1.2 ± 0.1% and 88% selectivity for formic acid), whereas the more crystalline sample prepared at pH = 9 was less active (ξ = 0.9 ± 0.1%) and leads to multiple oxidation products. The different behaviors were rationalized based on the role of oxygen vacancies as active adsorption and redox sites at the semiconductor surface, stablishing clear relationships between the semiconductor structure and its photocatalytic performance. The present work contributes for the rational development of specific photocatalysts for glycerol photoreforming.

A self-assembly strategy to synthesize carbon doped carbon nitride microtubes with a large π-electron conjugated system for efficient H2 evolution

The combination of element doping into carbon nitride and developing a novel structure is charming in realizing outstanding photocatalytic performance. Herein, carbon-doped carbon nitride microtubes with a large π-electron conjugated system were developed via a facile self-assembly strategy. Glucosamine hydrochloride, a substance with abundant hydroxyl and amino, and melamine were applied as precursors based on the self-assembly behavior via hydrogen bonds. The glucosamine hydrochloride content and the formation of hydrogen bond have impacts on self-assembly behavior to fabricate a rod-shaped precursor. Afterwards, carbon-doped carbon nitride microtubes are synthesized after calcination. The effective π delocalization induced by C doping and unique tubular morphology facilitate charge carrier transfer, offer plentiful active sites as well as the improved visible light capture efficiency. Therefore, carbon-doped carbon nitride microtubes display an outstanding H2 generation rate of 3888.9 μmol h−1 g−1 under λ > 400 nm, far beyond that of pure carbon nitride (886.3 μmol h−1 g−1). Experimental and density functional theory calculation demonstrate that carbon doping endows adjustable band structure, narrow band gap, enhanced π electron density and fast charge transfer rate, finally boosts photocatalytic activity. Our work gives a facial way for fabricating C doped carbon nitride with optimized structure and catalytic performance, which offers an efficient method to develop heteroatoms-doped carbon nitride.

Confinement Matters: Stabilization of CdS Nanoparticles inside a Postmodified MOF toward Photocatalytic Hydrogen Evolution.

Insights into developing innovative routes for the stabilization of photogenerated charge-separated states by suppressing charge recombination in photocatalysts is a topic of immense importance. Herein, we report the synthesis of a metal-organic framework (MOF)-based composite where CdS nanoparticles (NPs) are confined inside the nanosized pores of Zr4+-based MOF-808, namely, CdS@MOF-808. Anchoring l-cysteine into the nanospace of MOF-808 via postsynthetic ligand exchange allows the capture of Cd2+ ions from their aqueous solution, which are further utilized for in situ growth of CdS NPs inside the nanosized MOF pores. The formation of CdS@MOF-808 opens up a possibility for visible-light photocatalysis as CdS NPs (1-2 nm) are a well-studied semiconductor system with a band gap of ∼2.6 eV. The confinement of the CdS NPs inside the MOF pores, close to the Zr4+ cluster, opens up a shorter electron transfer route from CdS to the catalytic Zr4+ cluster and shows a high rate of H2 evolution (10.41 mmol g-1 h-1) from water with a loading of 3.56 wt % CdS. In contrast, a similar composite in which CdS NPs are stabilized on the external surface of MOF-808 reveals poor activity (0.15 mmol g-1 h-1). CdS NPs stabilized on the MOF-808 surface show slower and inefficient electron transfer kinetics compared to CdS stabilized inside the nanospace of the MOF, as realized by the transient absorption measurements. Therefore, this work unveils the critical role of stabilizing the photosensitizer NPs in close proximity of the catalytic sites in MOF systems towards developing highly efficient H2 evolution photocatalysts.

In‐Depth Understanding of the Effect of Halogen‐Induced Stable 2D Bismuth‐Based Perovskites for Photocatalytic Hydrogen Evolution Activity

AbstractHalide perovskites are excellent catalysts for photocatalytic hydrogen (H2) evolution; however, their instability in aqueous systems limits their applications. In this study, an alternative system is presented to avoid the ionization of halide perovskites based on ethanol splitting and three Bi‐based halide perovskite nanosheets (Cs3Bi2X9 PNs; X = I, Br, Cl) are prepared for H2 evolution. Small amounts of these halide perovskites possess good stability in ethanol, where the optimal Cs3Bi2I9 PNs exhibit the highest H2 evolution rate of 2157.8 µmol h−1 g−1. In particular, the effects of halogen regulation on the H2 evolution activity are investigated in depth from various perspectives for Cs3Bi2X9. The increased number of halogen atoms reduces the Bi···Bi distance in the octahedral configuration and eliminates the strong localization of electron–hole pairs, which are conducive to photogenerated charge separation and transfer. In addition, the dominant contribution of halogens to the conduction band is enhanced with an increase in the halogen atomic number. This study establishes a novel strategy for studying Bi‐based perovskites for optimizing their photocatalytic properties. Furthermore, it provides a new perspective for developing highly efficient and stable H2 evolution systems for halide perovskites.

Two-Step Process of a Crystal Facet-Modulated BiVO4 Photoanode for Efficiency Improvement in Photoelectrochemical Hydrogen Evolution.

The photoactivity of nanoporous bismuth vanadate (BiVO4, BVO) photoanodes that were fabricated by a two-step process (electrodeposition and then thermal conversion) in photoelectrochemical (PEC) hydrogen (H2) evolution can be enhanced about 1.44-fold by improving the constitutive ratio of (111̅), (061), and (242̅) crystal facets. The PEC characterization was carried out to investigate the factors altering the performance, which revealed that the crystal facet modulation could improve the photoactivity of the BVO photoanodes. In addition, the orientation-controlled BVO thin-film electrodes are introduced as evidence that the present crystal facet modulation is the positive effect for BVO photoanodes in PEC. The investigation of energy band structures and interfacial charge carrier dynamics of the BVO photoanodes reveals that the crystal facet modulation could result in a shorter lifetime of charge carrier recombination and larger band bending at the interface between BVO and electrolytes. This outcome could improve the charge separation and charge transfer efficiencies of BVO photoanodes, promoting the efficiency of PEC H2 evolution. Moreover, this crystal facet modulation can combine with co-catalyst decoration to further improve the solar-to-hydrogen efficiency of BVO photoanodes in PEC. This study presents a potential strategy to promote the PEC activity by crystal facet modulation and important insights into the interfacial charge transfer properties of semiconductor photoelectrodes for the application in solar fuel generation.

Reversible hydrogenation of carbon dioxide to formic acid using a Mn-pincer complex in the presence of lysine

Efficient hydrogen storage and release are essential for effective use of hydrogen as an energy carrier. In principle, formic acid could be used as a convenient hydrogen storage medium via reversible CO2 hydrogenation. However, noble metal-based catalysts are currently needed to facilitate the (de)hydrogenation, and the CO2 produced during hydrogen release is generally released, resulting in undesirable emissions. Here we report an α-amino acid-promoted system for reversible CO2 hydrogenation to formic acid using a Mn-pincer complex as a homogeneous catalyst. We observe good stability and reusability of the catalyst and lysine as the amino acid at high productivities (CO2 hydrogenation: total turnover number of 2,000,000; formic acid dehydrogenation: total turnover number of 600,000). Employing potassium lysinate, we achieve >80% H2 evolution efficiency and >99.9% CO2 retention in ten charge–discharge cycles, avoiding CO2 re-loading steps between each cycle. This process was scaled up by a factor of 18 without obvious drop of the productivity.

Modulation of the Band Bending of CdS by Fluorination to Facilitate Photoinduced Electron Transfer for Efficient H2 Evolution over Pt/CdS

The potential barrier (Schottky barrier), embodied in the upward band bending of an n-type semiconductor at the interface of a Pt-loaded semiconductor, often makes it difficult for the interfacial photoinduced electron transfer from the conduction band of the semiconductor to the loaded Pt, giving rise to the recombination probability of the photogenerated charges. In this work, we prepared fluorinated CdS by a facile hydrothermal process in the presence of NH4F. With the assistance of the noble metal Pt, the fluorinated CdS exhibits a superior photocatalytic H2 evolution to pristine CdS. Various characterization results revealed that the incorporation of the fluorine anions into the CdS lattice by fluorination apparently lowers the Fermi level to weaken the upward band bending of CdS at the Pt/CdS interface, favoring the interfacial photoinduced electron transfer from the conduction band of CdS to the loaded Pt for an efficient H2 evolution. This work highlights the role of weakening the potential barrier at the Pt/CdS interface in promoting the interfacial photoinduced electron transfer for efficient H2 evolution.

Carbon dots as solid-state electron mediator and electron acceptor in S-scheme heterojunction for boosted photocatalytic hydrogen evolution

Nowadays, it is still an attracting work to photocatalytic water splitting into hydrogen production using solar energy owing to its ecological and sustainable development significance. Herein, a ternary ZnIn2S4/carbon dots/g-C3N4 (ZIS/CDs/CN) S-scheme heterojunction photocatalyst with solid-state electron mediator and electron acceptor dual roles of CDs (∼5 nm) as a co-catalyst are designed via a calcination method follow-up water bath process for boosted photocatalytic H2 evolution. Compared to individual ZIS and pure CN, the photocatalytic efficiency of H2 evolution over ZIS/CDs/CN is enhanced by about 2 and 10 times, respectively. Combined with density functional theory (DFT) calculations, the heterojunction type between ZIS and CN is determined to be S-scheme heterojunction. In order to corroborate the role of CDs in S-scheme heterojunction, ZnIn2S4/g-C3N4 (ZIS/CN) was synthesized for comparative experiments and characterization, and its promotion of S-scheme heterojunction was confirmed. Furthermore, ZIS/CDs/CN S-scheme heterojunction photocatalyst still express excellent practicality in seawater environment and structural stability after four successive cycling reactions for photocatalytic H2 evolution. In addition, this bi-functional CDs is also applicable to S-scheme heterojunction constructed from other two different semiconductors, which enrich the construction method of later S-scheme heterojunctions and advance the development of S-scheme heterojunctions.

Well-defined core/shell pDA@Ni-MOF heterostructures with photostable polydopamine as electron-transfer-template for efficient photoelectrochemical H2 evolution

Here, novel core/shell polydopamine@Ni-MOF (pDA@Ni-MOF) heterogeneous nanostructures are synthesized via a simple one-pot nucleation-growth technique. This rational core/shell design method provide a uniform Ni-MOF shell thickness (shell: ∼ 10 nm) as well as homogeneous wrapping of pDA templates with quite narrow size distributions. The obtained band properties of bare pDA ( E CB = −0.35 eV and E VB = 2.95 eV vs normal hydrogen electrode (NHE)) and bare Ni-MOF ( E CB = −0.49 eV and E VB = 2.85 eV vs NHE) clearly revealed charge separation is occurred on pDA by absorbing light due to π-π∗ transition, and photogenerated electrons on conduction band (CB) of pDA was migrated to CB of Ni-MOF. Specifically, the photoelectrochemical (PEC) water performance of pDA@Ni-MOF photoanodes with highest current density is recorded as 8.61 mA/cm 2 at 0.77 V vs. RHE under visible LED irradiation, which is significantly higher than bare pDA (0.008 V vs. RHE) and bare Ni-MOF (0.011 V vs. RHE) at the same conditions. Note that, the higher photon absorption properties of pDA in core together with high interaction valence bond between two semiconductors could generate electron rich state giving rise to faster electron transfer kinetics as next generation of MOF based hybrid materials with regular morphologies. • One-pot nucleation-growth me-thod is utilized to produce core/shell pDA@Ni-MOF. • Charge separation is done on pDA by absorbing light due to π-π∗ transition. • Photogenerated electrons on pDA is migrated to Ni-MOF. • Highest current density is recorded as 8.61 mA/cm 2 at 0.77 V vs. RHE. • The charge transfer mechanism is verified by XPS.

Fabrication of a ternary NiS/ZnIn2S4/g-C3N4 photocatalyst with dual charge transfer channels towards efficient H2 evolution

As a renewable green energy, hydrogen has received widespread attention due to its huge potential in solving energy shortages and environment pollution. In this paper, a one-step solvothermal method was applied to grow ultra-thin g-C3N4 (UCN) nanosheets and NiS nanoparticles on the surface of ZnIn2S4 (ZIS). A ternary NiS/ZnIn2S4/ultra-thin-g-C3N4 composite material with dual high-speed charge transfer channels was constructed for the advancement of the photocatalytic H2 generation. The optimal ternary catalyst 1.5wt.%NiS/ZnIn2S4/ultra-thin-g-C3N4 (NiS/ZIS/UCN) achieved a H2 evolution yield reached to 5.02 mmolg−1h−1, which was 5.23 times superior than that of pristine ZnIn2S4 (0.96 mmolg−1h−1) and even outperform than that of the best precious metal modified 3.0 wt%Pt/ZnIn2S4 (4.08 mmolg−1h−1). The AQY at 420 nm could be achieved as high as 30.5%. The increased photocatalytic performance of NiS/ZIS/UCN could be ascribed to the type-I heterojunctions between intimated ZIS and UCN. In addition, NiS co-catalyst with large quantity of H2 evolution sites, could result in efficient photo-induced charges separation and migration. Furthermore, the NiS/ZIS/UCN composite exhibited excellent H2 evolution stability and recyclability. This work would also offer a reference for the design and synthesis of ternary co-catalyst with heterojunction composite for green energy conversion.

NiSx modified Mn0.5Cd0.5S twinned homojunctions for efficient photocatalytic hydrogen evolution

Twinned Mn0.5Cd0.5S homojunction (T-MCS) was synthesized via a simple hydrothermal process, and then NiSx was precipitated on the surface of T-MCS by in situ precipitation process. The type-II staggered band alignment between zinc-blende (ZB) and wurtzite (WZ) Mn0.5Cd0.5S can form a homojunction in bulk T-MCS, and the introduction of NiSx nanoparticles can construct a heterojunction between NiSx and T-MCS. The synergistic of homojunction and heterojunction can effectively promote the separation of charge carriers in the bulk phase and surface of T-MCS, meanwhile, NiSx can reduce the H2 evolution overpotential and induce more active sites, leading to an increased H2 production efficiency. The 0.5 wt% NiSx/T-MCS shows a great H2 evolution rate of 111.5 mmol∙g−1∙h−1 in Na2S/Na2SO3 solution under visible light (λ ≥ 420 nm) irradiation, which is 2.3-fold higher than that of the pure T-MCS. Its apparent quantum efficiency (AQE) is 10.4% under 400 (±5) nm light irradiation. This research sheds light on the exploration of homo-heterojunction photocatalysts for efficient H2 evolution.

Unique Mo2C–CdS–Co@C heterojunction integrated with redox cocatalysts and multiple active sites for efficient photocatalytic H2 generation

Photocatalytic water-splitting has encouraged great interest to obtain renewable H2 fuel via the transformation of solar energy. Although significant progress has been achieved, realizing efficient H2 evolution reaction (HER) with non-noble-metal photocatalysts is still challenging. Herein, we report a facile synthesis of Mo2C–CdS–[email protected] heterojunction by anchoring CdS and Mo2C nanoparticles onto [email protected] micro-flowers. The [email protected] micro-flowers were composed of graphitic carbon nanoflakes partially embedded with Co, CoOx, Co9S8 nanocrystals and obtained through the carbonization of metanilic-anion intercalated Co(OH)2 precursor. Due to excellent visible-light harvesting capacity, efficient charge transmission and isolation caused by the existence of superior electron mediator (graphitic carbon) together with oxidation (CoOx) and reduction (Co, Co9S8, Mo2C) cocatalysts, as well as the plentiful H2-evolving active sites originating from the metal (Co), metal sulfide (Co9S8), and metal carbide (Mo2C), the Mo2C–CdS–[email protected] hybrid micro-flowers delivered an exceptional HER (λ > 400 nm) activity of 760.58 μmol h−1 (10 mg), approximately 32 and 15 folds that of pristine CdS and platinum (3 wt%)-decorated CdS, respectively. Moreover, both the cycling and long-term photocatalytic tests confirm that the Mo2C–CdS–[email protected] possesses an outstanding durability for H2 production. The study results might inspire the rational integration of cocatalysts to simultaneously optimize the charge trapping and H2-evolving kinetics for strengthening the photocatalytic HER activity efficiently.

A promoted photocatalysis system trade-off between thermodynamic and kinetic via hierarchical distribution dual-defects for efficient H2 evolution

The tradeoff between thermodynamic and kinetic factors in a photocatalytic system to enhance its activity is still a challenging issue. The modificatin of a photocatalyst with defects provides an effective way to adjust the light absorption properties, but it may lead to the loss of kinetic factors. Herein, a strategy of constructing dual-defects is demonstrated to address this challenge. Bulk N doping and surface oxygen vacancies are introduced into black TiO2 nanotube array in hierarchies through the introduction of N source during anodization process and secondary aluminothermic reduction, respectively. The co-existing of dual-defects reduces the band-gap through p-orbital modulation, and the constant conduction band position ensures the preservation of thermodynamic capabilities. Moreover, a built-in electric field is formed owing to the different electrical properties between hierarchical distributions of dual-defects, which establishes the channels for efficient charge transfer. The thermodynamic and kinetic factors of the tradeoff are realized by the broadening of light absorption induced by “correct concentration” of dual-defects and the acceleration of photogenerated charge transfer induced by “correct distribution” of dual-defects, respectively. As a result, the hierarchically modified black TiO2 exhibits robust hydrogen evolution activity of 3183 μmol·g−1·h−1, roughly a 21-fold improvement with respect to pristine TiO2 under visible light illumination.

A novel hierarchical CdS-DETA@CoP composite as highly stable photocatalyst for efficient H2 evolution from water splitting under visible light irradiation

The photolysis of water using photocatalysts under sunlight irradiation for hydrogen generation reaction is an efficient strategy to solve energy and environmental issues. Herein, a novel hierarchical CdS-DETA@CoP composite was fabricated and applied to visible-light-driven photocatalytic water splitting for generating H2. To achieve this goal, we first prepared a 3D hierarchical CoP co-catalyst via direct phosphatization of the ZIF-67 precursor. Then, two-dimensional (2D) CdS-DETA nanosheets were in situ grown on the surface of hierarchical CoP through a facile water bath method, obtaining a CdS-DETA@CoP composite with a high surface area. The CdS-DETA@CoP composite with 20 wt% CoP exhibits a maximum photocatalytic H2 evolution rate of 48.76 mmol g–1h−1 under visible light irradiation with lactic acid as the sacrificial reagent, which is 46.4 times as high as CdS-DETA. The synergistic effect between CdS-DETA and CoP induced remarkable ability of light-harvesting and efficient separation of photogenerated electron-hole pairs, thus profoundly promoting the activity and stability. The excellent activity is also closely related to the better dispersion of CdS-DETA on the surface of hierarchical CoP co-catalyst.

Nitrogen-defect induced trap states steering electron-hole migration in graphite carbon nitride

Defect structures of semiconductors intrinsically regulate the trap states, excitons and active charge carriers for artificial photosynthesis systems. A g-C3N4 system with abundant nitrogen defects was prepared through a thermal polycondensation strategy to reveal the role of trap states and exhibited a 20-fold enhanced H2 evolution efficiency relative to bulk g-C3N4 under visible light irradiation. Subsequent femtosecond transient absorption spectroscopy study found that the N-defect induced shallow trap states can capture photogenerated electrons to inhibit deep trapping and direct recombination of photogenerated charges. The active electrons in shallow trap states can enhance the photocatalytic H2 evolution when compared with the inactive electrons in deep trap states. Mid-infrared transient absorption spectroscopy also confirmed the increased quantity of shallow-trapped electrons without interference of other signals. This work provides new insights for steering depth of trap states and photocatalytic processes through N defects to achieve high photocatalytic performance using femtosecond transient absorption spectroscopy.

Indium-Based Metal-Organic Framework for Efficient Photocatalytic Hydrogen Evolution.

In this work, an indium-based metal-organic framework was successfully constructed, namely, as In-MOF, by elaborately selecting an InIII center with unique properties and a functional tetracarboxylic acid with unsaturated and open-coordinated nodes. Interestingly, the InIII center was connected to a single-metal-node-based porous three-dimensional pts net. Its structure was dentified by single-crystal and powder X-ray diffraction, Fourier transform infrared, thermogravimetric analysis, etc. Considering the special luminescent characteristic of an indium-based framework, as-prepared In-MOF was explored as a photocatalyst for H2 production from water splitting. The testing results demonstrate that In-MOF as a promising photocatalyst with a suitable band gap realizes a H2 evolution efficiency of 777.65 μmol g-1 h-1.

Piezoelectric nanofoams with the interlaced ultrathin graphene confining Zn–N–C dipoles for efficient piezocatalytic H2 evolution under low-frequency vibration

Unique nanofoams consisting of interweaved ultrathin graphene confining Zn–N–C dipoles (ZnNG) are constructed via calcination of Zn-coordinated precursor. Due to the introduction of local polar Zn–N–C configurations, with hypersensitivity for mechanical stress, the piezoelectricity is created on the nonpiezoelectric graphene, and the hierarchical ZnNG exhibits obvious piezocatalytic activity of water splitting for H2 production even under mild agitation. The corresponding rate of H2 production is about 14.65 μmol g−1 h−1. It triggers a breakthrough in piezocatalytic H2 evolution under low-frequency vibration, and takes a significant step forward for piezocatalysis towards practical applications. Furthermore, the presented concept of confining atomic polar configuration for engineering piezoelectricity would open up new horizon for constructing new-type piezoelectrics based on both piezoelectric and nonpiezoelectric materials.