Guigao Liu

Active Sites Implanted Carbon Cages in Core–Shell Architecture: Highly Active and Durable Electrocatalyst for Hydrogen Evolution Reaction

Low efficiency and poor stability are two major challenges we encounter in the exploration of non-noble metal electrocatalysts for the hydrogen evolution reaction (HER) in both acidic and alkaline environment. Herein, the hybrid of cobalt encapsulated by N, B codoped ultrathin carbon cages (Co@BCN) is first introduced as a highly active and durable nonprecious metal electrocatalysts for HER, which is constructed by a bottom-up approach using metal organic frameworks (MOFs) as precursor and self-sacrificing template. The optimized catalyst exhibited remarkable electrocatalytic performance for hydrogen production from both both acidic and alkaline media. Stability investigation reveals the overcoating of carbon cages can effectively avoid the corrosion and oxidation of the catalyst under extreme acidic and alkaline environment. Electrochemical active surface area (EASA) evaluation and density functional theory (DFT) calculations revealed that the synergetic effect between the encapsulated cobalt nanoparticle and the N, B codoped carbon shell played the fundamental role in the superior HER catalytic performance.

Targeted Synthesis of 2H- and 1T-Phase MoS2 Monolayers for Catalytic Hydrogen Evolution.

Through a facile and effective strategy by employing lithium molten salts the controlled synthesis of 2H- and 1T-MoS2 monolayers with high-yield production is achieved. Both phases of MoS2 monolayers exhibit high stabilities. When used as a catalyst for hydrogen evolution, these phased MoS2 monolayers deliver respective advantages in the field of electro- and photo-catalytic hydrogen evolution.

Efficient Visible‐Light‐Driven Carbon Dioxide Reduction by a Single‐Atom Implanted Metal–Organic Framework

Modular optimization of metal-organic frameworks (MOFs) was realized by incorporation of coordinatively unsaturated single atoms in a MOF matrix. The newly developed MOF can selectively capture and photoreduce CO2 with high efficiency under visible-light irradiation. Mechanistic investigation reveals that the presence of single Co atoms in the MOF can greatly boost the electron-hole separation efficiency in porphyrin units. Directional migration of photogenerated excitons from porphyrin to catalytic Co centers was witnessed, thereby achieving supply of long-lived electrons for the reduction of CO2 molecules adsorbed on Co centers. As a direct result, porphyrin MOF comprising atomically dispersed catalytic centers exhibits significantly enhanced photocatalytic conversion of CO2 , which is equivalent to a 3.13-fold improvement in CO evolution rate (200.6 μmol g-1  h-1 ) and a 5.93-fold enhancement in CH4 generation rate (36.67 μmol g-1  h-1 ) compared to the parent MOF.

Promoting Active Species Generation by Plasmon-Induced Hot-Electron Excitation for Efficient Electrocatalytic Oxygen Evolution

Water splitting represents a promising technology for renewable energy conversion and storage, but it is greatly hindered by the kinetically sluggish oxygen evolution reaction (OER). Here, using Au-nanoparticle-decorated Ni(OH)2 nanosheets [Ni(OH)2-Au] as catalysts, we demonstrate that the photon-induced surface plasmon resonance (SPR) excitation on Au nanoparticles could significantly activate the OER catalysis, specifically achieving a more than 4-fold enhanced activity and meanwhile affording a markedly decreased overpotential of 270 mV at the current density of 10 mA cm(-2) and a small Tafel slope of 35 mV dec(-1) (no iR-correction), which is much better than those of the benchmark IrO2 and RuO2, as well as most Ni-based OER catalysts reported to date. The synergy of the enhanced generation of Ni(III/IV) active species and the improved charge transfer, both induced by hot-electron excitation on Au nanoparticles, is proposed to account for such a markedly increased activity. The SPR-enhanced OER catalysis could also be observed over cobalt oxide (CoO)-Au and iron oxy-hydroxide (FeOOH)-Au catalysts, suggesting the generality of this strategy. These findings highlight the possibility of activating OER catalysis by plasmonic excitation and could open new avenues toward the design of more-energy-efficient catalytic water oxidation systems with the assistance of light energy.

Surface-Plasmon-Enhanced Photodriven CO2 Reduction Catalyzed by Metal-Organic-Framework-Derived Iron Nanoparticles Encapsulated by Ultrathin Carbon Layers.

Highly efficient utilization of solar light with an excellent reduction capacity is achieved for plasmonic Fe@C nanostructures. By carbon layer coating, the optimized catalyst exhibits enhanced selectivity and stability applied to the solar-driven reduction of CO2 into CO. The surface-plasmon effect of iron particles is proposed to excite CO2 molecules, and thereby facilitates the final reaction activity.

In situ synthesis of ordered mesoporous Co-doped TiO2 and its enhanced photocatalytic activity and selectivity for the reduction of CO2

Ordered mesoporous cobalt-doped titanium dioxide was successfully synthesized by a multicomponent self-assembly process. The doped Co species change the construction of the conduction band and valence band of TiO2, leading to visible-light absorption for TiO2. The designed cobalt-doped titanium dioxide exhibits a higher visible light activity for the reduction of CO2 among the commonly reported photocatalysts. In addition, the selectivity of the reduction products is improved by optimizing the energy-band configurations of cobalt-doped titanium dioxide through varying the molar ratio of Co/Ti. When the doping content of cobalt species increases to some extent, Co3O4/Co-doped TiO2 nanocomposites with oxygen vacancies were obtained, which markedly improve the generation rate of CH4.

Band-structure-controlled BiO(ClBr)(1−x)/2Ix solid solutions for visible-light photocatalysis

A group of BiO(ClBr)(1−x)/2Ix solid solutions with a homogeneous layered tetragonal matlockite structure have been explored as novel visible-light-active photocatalysts. By manipulating the composition ratio of halogen elements (I/(Cl + Br)), the band gaps of these Bi-based solid solutions can be continuously modulated in a rather wide range of 2.88 to 1.82 eV. The density functional calculations demonstrate that this continuous band gap narrowing originates from the gradual increase of valence band maximum with increasing ratio of I/(Cl + Br). The photocatalytic evaluations showed these materials possess composition-dependent photoactivities for degrading 2-propanol (IPA) to acetone and CO2 under visible light (400 < λ < 800 nm). Particularly, the highest acetone evolution rate (215.6 μmol h−1 g−1) was achieved over BiO(ClBr)0.21I0.58, which was 16.5, 11.8 and 659.3 times that of BiO(ClBr)0.5, BiOI and commercial Bi2O3, respectively. And BiO(ClBr)0.375I0.25 exhibited the best photocatalytic performance for CO2 evolution (4.8 μmol h−1 g−1, 2.3 and 23.2 times that of BiO(ClBr)0.5 and BiOI, respectively). In addition, a composition-dependent photocatalysis mechanism is proposed in detail and it involves the indirect hole-induced ˙OH oxidation or direct hole oxidation of IPA molecules in valence bands and simultaneous electron reduction of oxygen to H2O2 in conduction bands. This work not only shows that BiO(ClBr)(1−x)/2Ix photocatalysts hold great promise for practical applications but also proves that fabricating solid solutions is an effective approach to develop highly efficient visible-light photocatalysts.

Superior Photocatalytic H2 Production with Cocatalytic Co/Ni Species Anchored on Sulfide Semiconductor

Downsizing transition metal-based cocatalysts on semiconductors to promote photocatalytic efficiency is important for research and industrial applications. This study presents a novel and facile strategy for anchoring well-dispersed metal species on CdS surface through controlled decarboxylation of the ethylenediaminetetraacetate (EDTA) ligand in the metal-EDTA (M-EDTA) complex and CdS mixture precursor to function as a cocatalyst in the photocatalytic H2 evolution. Microstructure characterization and performance evaluation reveal that under visible light the resulting pentacoordinated Co(II) and hexacoordinated Ni(II) on CdS exhibits a high activity of 3.1 mmol h-1 (with turnover frequency (TOF) of 626 h-1 and apparent quantum efficiency (AQE) of 56.2% at 420 nm) and 4.3 mmol h-1 (with TOF of 864 h-1 and AQE of 67.5% at 420 nm), respectively, toward cocatalytic hydrogen evolution, and the cocatalytic activity of such a hexacoordinated Ni(II) even exceeds that of platinum. Further mechanistic study and theoretical modeling indicate that the fully utilized Co(II)/Ni(II) active sites, efficient charge transfer, and favorable kinetics guarantee the efficient activities. This work introduces a promising precursor, i.e., M-EDTA for planting well-dispersed transition metal species on the sulfide supports by a facile wet-chemistry approach, providing new opportunities for photocatalytic H2 production at the atomic/molecular scale.

Crystal-facet-dependent hot-electron transfer in plasmonic-Au/semiconductor heterostructures for efficient solar photocatalysis

Here, using Au–BiOCl as models, we show the significant crystal facet effects of the semiconductor on hot-electron transfer within such plasmonic heterostructures under visible light. It is found that {010} facets of BiOCl are greatly advantageous over {001} facets for the hot-electron injection, as evidenced by steady-state diffuse reflectance spectroscopy and photoelectrochemical measurements. Consequently, Au–BiOCl-010 exhibits superior activity for photocatalytic aerobic oxidation of 2-propanol with a quantum efficiency of 1.3%, being 3.5 times higher than that of Au–BiOCl-001. The differences in band structure between the {001} and {010} facets of BiOCl may account for the facet-dependent hot-electron transfer characteristics.

Improved Photocatalytic H2 Evolution over G‐Carbon Nitride with Enhanced In‐Plane Ordering

A series of rod-like porous graphitic-carbon nitrides (short as CNs) with enhanced in-plane ordering have been fabricated through self-assembled heptazine hydrate precursors for the first time. By controlling the calcination of the preformed precursors with different temperature-rising rates, the resulted CNs (SAHEP-CNs-1) with the most ordered and least stacked graphitic planar are showing a tremendously improved hydrogen evolution rate of 420 μmol h-1 under visible light and a remarkable apparent quantum efficiency of 8.9% at 420 nm, which is among the highest values for C3 N4 -related photocatalysts in the literature. This work discloses that enhancing in-plane ordering is one critical factor for improving the photocatalytic H2 evolution of carbon nitride, which is an effective solution to prolong the lifetime of charge carriers by accelerating the charge transport and separation within the graphitic planar. This finding would present a facial strategy for the designing of efficient organic semiconductors for photocatalysis.