Single-Atom Pt Doping Induced p-Type to n-Type Transition in NiO Nanosheets toward Self-Gating Modulated Electrocatalytic Hydrogen Evolution Reaction.

Exploring highly efficient single atom catalysts with defined active centers and tunable electronic structures is highly desirable. Herein, we developed an efficient hydrogen evolution reaction (HER) electrocatalyst through a self-gating phenomenon induced by Pt single atoms (SAs) supported on ultrathin NiO nanosheets (PtSA-NiO). The Ni atoms in NiO are partially replaced by the atomically dispersed Pt atoms, leading to a transition from p-type NiO into n-type PtSA-NiO. When the n-type PtSA-NiO serves as HER electrocatalyst, the self-gating phenomenon occurs in the ultrathin nanosheets, resulting in a mixture of leakage ("active") and metal-insulator-semiconductor ("inert") regions. The "inert" region induced by the ionic gating and reverse potential is capable of accumulating relatively high surface charge carrier concentration with an ultrahigh electric field, making the PtSA-NiO highly conductive; meanwhile, the HER process occurs at the Pt SAs sites (active region) in the PtSA-NiO nanosheets. As a result, the PtSA-NiO requires only 55 mV to deliver 10 mA/cm2 in an alkaline solution with good stability.

Selective photoelectrochemical oxidation of glucose to glucaric acid by single atom Pt decorated defective TiO2.

Photoelectrochemical reaction is emerging as a powerful approach for biomass conversion. However, it has been rarely explored for glucose conversion into value-added chemicals. Here we develop a photoelectrochemical approach for selective oxidation of glucose to high value-added glucaric acid by using single-atom Pt anchored on defective TiO2 nanorod arrays as photoanode. The defective structure induced by the oxygen vacancies can modulate the charge carrier dynamics and band structure, simultaneously. With optimized oxygen vacancies, the defective TiO2 photoanode shows greatly improved charge separation and significantly enhanced selectivity and yield of C6 products. By decorating single-atom Pt on the defective TiO2 photoanode, selective oxidation of glucose to glucaric acid can be achieved. In this work, defective TiO2 with single-atom Pt achieves a photocurrent density of 1.91 mA cm-2 for glucose oxidation at 0.6 V versus reversible hydrogen electrode, leading to an 84.3 % yield of glucaric acid under simulated sunlight irradiation.

Sub-10 nm Corrugated TiO2 Nanowire Arrays by Monomicelle-Directed Assembly for Efficient Hole Extraction.

Precise synthesis of well-ordered ultrathin nanowire arrays with tunable active surface, though attractive in optoelectronics, remains challenging to date. Herein, well-aligned sub-10 nm TiO2 nanowire arrays with controllable corrugated structure have been synthesized by a unique monomicelle-directed assembly method. The nanowires with an exceptionally small diameter of ∼8 nm abreast grow with an identical adjacent distance of ∼10 nm, forming vertically aligned arrays (∼800 nm thickness) with a large surface area of ∼102 m2 g-1. The corrugated structure consists of bowl-like concave structures (∼5 nm diameter) that are closely arranged along the axis of the ultrathin nanowires. And the diameter of the concave structures can be finely manipulated from ∼2 to 5 nm by simply varying the reaction time. The arrays exhibit excellent charge dynamic properties, leading to a high applied bias photon-to-current efficiency up to 1.4% even at a very low potential of 0.41 VRHE and a superior photocurrent of 1.96 mA cm-2 at 1.23 VRHE. Notably, an underlying mechanism of the hole extraction effect for concave walls is first clarified, demonstrating the exact role of concave walls as the hole collection centers for efficient water splitting.

Highly Active and Durable Single-Atom Tungsten-Doped NiS0.5 Se0.5 Nanosheet @ NiS0.5 Se0.5 Nanorod Heterostructures for Water Splitting.

Developing robust and highly active non-precious electrocatalysts for the hydrogen/oxygen evolution reaction (HER/OER) is crucial for the industrialization of hydrogen energy. In this study, a highly active and durable single-atom W-doped NiS0.5 Se0.5 nanosheet @ NiS0.5 Se0.5 nanorod heterostructure (W-NiS0.5 Se0.5 ) electrocatalyst is prepared. W-NiS0.5 Se0.5 exhibits excellent catalytic activity for the HER and OER with ultralow overpotentials (39 and 106 mV for the HER and 171 and 239 mV for the OER at 10 and 100 mA cm-2 , respectively) and excellent long-term durability (500 h), outperforming commercial precious-metal catalysts and many other previously reported transition-metal-based compounds (TMCs). The introduction of single-atom W delocalizes the spin state of Ni, which results in an increase in the Ni d-electron density. This causes the optimization of the adsorption/desorption process of H and a significant reduction in the adsorption free energy of the rate-determining step (O* → OOH*), thus accelerating the thermodynamics and kinetics of the HER and OER. This work provides a rational feasible strategy to design single-atom catalysts for water splitting and to develop advanced TMC electrocatalysts by regulating delocalized spin states.

Efficient photocatalytic hydrogen peroxide generation coupled with selective benzylamine oxidation over defective ZrS3 nanobelts.

Photocatalytic hydrogen peroxide (H2O2) generation represents a promising approach for artificial photosynthesis. However, the sluggish half-reaction of water oxidation significantly limits the efficiency of H2O2 generation. Here, a benzylamine oxidation with more favorable thermodynamics is employed as the half-reaction to couple with H2O2 generation in water by using defective zirconium trisulfide (ZrS3) nanobelts as a photocatalyst. The ZrS3 nanobelts with disulfide (S22-) and sulfide anion (S2-) vacancies exhibit an excellent photocatalytic performance for H2O2 generation and simultaneous oxidation of benzylamine to benzonitrile with a high selectivity of >99%. More importantly, the S22- and S2- vacancies can be separately introduced into ZrS3 nanobelts in a controlled manner. The S22- vacancies are further revealed to facilitate the separation of photogenerated charge carriers. The S2- vacancies can significantly improve the electron conduction, hole extraction, and kinetics of benzylamine oxidation. As a result, the use of defective ZrS3 nanobelts yields a high production rate of 78.1 ± 1.5 and 32.0 ± 1.2 µmol h-1 for H2O2 and benzonitrile, respectively, under a simulated sunlight irradiation.

2H-NbS2 film as a novel counter electrode for meso-structured perovskite solar cells.

We report the use of 2H-NbS2 film as a novel counter electrode in perovskite solar cells fabricated with a cold isostatic pressing method. The 2H-NbS2 film, which was prepared through an exfoliation method followed by restacking from LixNbS2 powder, shows high electrical conductivity of 8.7 × 103 S cm-1 and work function of 5.20 eV. The two-dimensional transition metal dichalcogenide was used for the first time as a counter electrode in meso-structured perovskite solar cells. Through this process, we demonstrated a new alternative to noble metals. The perovskite solar cell base on the 2H-NbS2 counter electrode showed an open-circuit voltage of 1.046 V, comparable to that of gold, and a power conversion efficiency of 8.3%.

Controllable reduced black titania with enhanced photoelectrochemical water splitting performance.

Black titania prepared by metal-reduction methods is systematically studied and found the best controllable Mg-reduction method. Colored titania products from white, light blue, dark blue, to black were obtained with a crystalline/amorphous core-shell structure. The black titania shows a five times higher H2 production rate in photoelectrochemical (PEC) water splitting.

Hydrogenated blue titania with high solar absorption and greatly improved photocatalysis.

Hydrogenated black titania, with a crystalline core/amorphous shell structure, has attracted global interest due to its excellent photocatalytic properties. However, the understanding of its structure-property relationships remains a great challenge and a more effective method to produce hydrogenated titania is desirable. Herein, we report a TiH2 assisted reduction method to synthesize bluish hydrogenated titania (TiO2-x:H) that is highly crystallized. The characteristic amorphous shells, which are essential for the enhancement of solar absorption and photocatalysis in many reported hydrogenated titania, are completely removed by hydrogen peroxide. The blue TiO2-x:H sample without amorphous shells delivers not only significantly improved visible- and infrared-light absorption but also greatly enhanced photocatalytic activity compared to pristine TiO2. Its water decontamination is 2.5 times faster and the hydrogen production was 1.9-fold higher over pristine TiO2. Photoelectrochemical measurement reveals greatly improved carrier density and photocurrent (a 4.3-fold increase) in the reduced TiO2-x:H samples. This work develops a facile and versatile method to prepare hydrogenated titania and proposes a new understanding of the hydrogenated titania that doped hydrogen atoms, instead of the amorphous shells, are essential for its high photocatalytic performance.