Showing papers by "Yanguang Li published in 2015"

Recent advances in heterogeneous electrocatalysts for the hydrogen evolution reaction

Abstract: The hydrogen evolution reaction plays a decisive role in a range of electrochemical and photoelectrochemical devices. It requires efficient and robust electrocatalysts to lower the reaction overpotential and minimize energy consumption. Over the last decade, we have witnessed a rapid rise in new electrocatalysts, particularly those based on non-precious metals. Some of them approach the activity of precious metal benchmarks. Here, we present a comprehensive overview of the recent developments of heterogeneous electrocatalysts for the hydrogen evolution reaction. Detailed discussion is organized from precious metals to non-precious metal compounds including alloys, chalcogenides, carbides, nitrides, borides and phosphides, and finally to metal-free materials. Emphasis is placed on the challenges facing these electrocatalysts and solutions for further improving their performance. We conclude with a perspective on the development of future HER electrocatalysts.

Ultrathin MoS2(1–x)Se2x Alloy Nanoflakes For Electrocatalytic Hydrogen Evolution Reaction

Abstract: The development of non precious metal based electrocatalysts for the hydrogen evolution reaction (HER) holds a decisive key to a spectrum of energy conversion technologies. Previous studies have established layered molybdenum chalcogenides as promising candidates. In this work, we prepared ultrathin MoS2(1–x)Se2x alloy nanoflakes with monolayer or few-layer thickness and fully tunable chemical composition for maximum HER activity. Spectroscopic characterizations corroborate the progressive evolution of their structures and properties as x increases from 0 to 1 without any noticeable phase separation. In particular, it is evidenced that the introduction of selenium continuously modulates the d band electronic structure of molybdenum, probably leading to tuned hydrogen adsorption free energy and consequently electrocatalytic activity. Electrochemical measurements show that all MoS2(1–x)Se2x nanoflakes are highly active and durable for HER with small overpotentials in the range of 80–100 mV and negligible ac...

Highly active and durable methanol oxidation electrocatalyst based on the synergy of platinum-nickel hydroxide-graphene.

Abstract: Active and durable electrocatalysts for methanol oxidation reaction are of critical importance to the commercial viability of direct methanol fuel cell technology. Unfortunately, current methanol oxidation electrocatalysts fall far short of expectations and suffer from rapid activity degradation. Here we report platinum-nickel hydroxide-graphene ternary hybrids as a possible solution to this long-standing issue. The incorporation of highly defective nickel hydroxide nanostructures is believed to play the decisive role in promoting the dissociative adsorption of water molecules and subsequent oxidative removal of carbonaceous poison on neighbouring platinum sites. As a result, the ternary hybrids exhibit exceptional activity and durability towards efficient methanol oxidation reaction. Under periodic reactivations, the hybrids can endure at least 500,000 s with negligible activity loss, which is, to the best of our knowledge, two to three orders of magnitude longer than all available electrocatalysts.

Ultrathin nickel–iron layered double hydroxide nanosheets intercalated with molybdate anions for electrocatalytic water oxidation

Abstract: There have been growing efforts to search for active, robust and cost-effective electrocatalysts for the oxygen evolution reaction (OER). Among the different candidates, Ni–Fe layered double hydroxides (LDHs) hold great promise due to their high activity closely approaching or even outperforming that of the precious metal benchmark in alkaline media. Here, we show that their activity can be further promoted when forming ultrathin LDH nanosheets intercalated with molybdate ions via an exfoliation-free hydrothermal method. In 1 M KOH, these nanosheets exhibit about 3-fold higher OER current density than regular NiFe LDH nanosheets, which was believed to be mostly contributed by their higher available density of electrochemically active sites associated with the ultrathin thickness. The great activity is also accompanied by remarkable durability at different current density levels. Finally, we demonstrate that these ultrathin nanosheets can also be directly grown on Ni foam for achieving significant current densities.

In Situ X-ray Absorption Near-Edge Structure Study of Advanced NiFe(OH)x Electrocatalyst on Carbon Paper for Water Oxidation

Abstract: A promising NiFe(OH)x catalyst for oxygen evolution reaction (OER) has been successfully fabricated and studied in detail using in situ X-ray absorption near-edge structure (XANES) spectroscopy. The chemical nature of elements (Ni, Fe) in electrocatalysts has been elucidated from Fe and Ni K- and L-edge XANES. The increase of oxidation states of Ni from Ni(III) to Ni(3.6) together with a highly covalent Fe(IV)–O bond under OER process is observed. Charge transfer between Ni and Fe through a “Ni–O–Fe” bond is proposed, accounting for the high catalytic activities of NiFe(OH)x.

Nanostructured CuP2/C composites as high-performance anode materials for sodium ion batteries

Abstract: Research on sodium ion batteries has recently been revived. Attention is now placed on the development of high-capacity and stable electrode materials at low costs. Among them, compounds operating on the conversion mechanism represent a promising class of anode materials. Unfortunately, they are generally plagued by poor electrical conductivity and large volume changes during repeated cycling. In this study, we exploit a new type of composite material made of copper phosphide and Super P carbon black (CuP2/C) as a potential anode candidate. The final products consisted of crystalline CuP2 cores coated with carbon black nanoparticles on the surface. Electrochemical measurements and multiple ex situ studies demonstrate that CuP2/C composites are capable of fast and reversible sodiation and desodiation based on the conversion mechanism. They deliver a large capacity in excess of 500 mA h g−1, high rate capability and decent short-term cycling stability. Our study suggests that these transition metal phosphides with a suitable carbon coating may hold great opportunities as anode materials for sodium ion batteries for effective and economical energy storage.

MoSe2 porous microspheres comprising monolayer flakes with high electrocatalytic activity

Abstract: A facile colloidal route to synthesize MoSe2 porous microspheres with diameters of 400–600 nm made up of MoSe2 monolayer flakes (∼0.7 nm in thickness) is reported. The solvents trioctylamine (TOA) and oleylamine (OAM) are found to play important roles in the formation of MoSe2 microspheres, whereby TOA determines the three-dimensional (3D) microspherical morphology and OAM directs the formation of MoSe2 monolayer flakes. The robust 3D MoSe2 microspheres exhibit remarkable activity and durability for the electrocatalytic hydrogen evolution reaction (HER) in acid, maintaining a small onset overpotential of ∼77 mV and keeping a small overpotential of 100 mV for a current density of 5 mA/cm2 after 1,000 cycles. In addition, similar 3D WSe2 microspheres can also be prepared by using this method. We expect this facile colloidal route could further be expanded to synthesize other porous structures which will find applications in fields such as in energy storage, catalysis, and sensing.

Nickel-coated silicon photocathode for water splitting in alkaline electrolytes

Abstract: Photoelectrochemical (PEC) water splitting is a promising approach to harvest and store solar energy [1]. Silicon has been widely investigated for PEC photoelectrodes due to its suitable band gap (1.12 eV) matching the solar spectrum [2]. Here we investigate employing nickel both as a catalyst and protecting layer of a p-type silicon photocathode for photoelectrochemical hydrogen evolution in basic electrolytes for the first time. The silicon photocathode was made by depositing 15 nm Ti on a p-type silicon wafer followed by 5 nm Ni. The photocathode afforded an onset potential of ∼0.3 V vs. the reversible hydrogen electrode (RHE) in alkaline solution (1 M KOH). The stability of the Ni/Ti/p-Si photocathode showed a 100 mV decay over 12 h in KOH, but the stability was significantly improved when the photocathode was operated in potassium borate buffer solution (pH ≈ 9.5). The electrode surface was found to remain intact after 12 h of continuous operation at a constant current density of 10 mA/cm2 in potassium borate buffer, suggesting that Ni affords good protection of Si based photocathodes in borate buffers.

Controllably Interfacing with Ferroelectric Layer: A Strategy for Enhancing Water Oxidation on Silicon by Surface Polarization.

Abstract: Silicon (Si) is an important material in photoelectrochemical (PEC) water splitting because of its good light-harvesting capability as well as excellent charge-transport properties. However, the shallow valence band edge of Si hinders its PEC performance for water oxidation. Generally, thanks to their deep valence band edge, metal oxides are incorporated with Si to improve the performance, but they also decrease the transportation of carriers in the electrode. Here, we integrated a ferroelectric poly(vinylidene fluoride–trifluoroethylene) [P(VDF–TrFE)] layer with Si to increase the photovoltage as well as the saturated current density. Because of the prominent ferroelectric property from P(VDF–TrFE), the Schottky barrier between Si and the electrolyte can be facially tuned by manipulating the poling direction of the ferroelectric domains. The photovoltage is improved from 460 to 540 mV with a forward-poled P(VDF–TrFE) layer, while the current density increased from 5.8 to 12.4 mA/cm2 at 1.23 V bias versus...