Guangyin Fan

Encased Copper Boosts the Electrocatalytic Activity of N-Doped Carbon Nanotubes for Hydrogen Evolution

Nitrogen (N)-doped carbons combined with transition-metal nanoparticles are attractive as alternatives to the state-of-the-art precious metal catalysts for hydrogen evolution reaction (HER). Herein, we demonstrate a strategy for fabricating three-dimensional (3D) Cu-encased N-doped carbon nanotube arrays which are directly grown on Cu foam (Cu@NC NT/CF) as a new efficient HER electrocatalyst. Cu nanoparticles are encased here instead of common transition metals (Fe, Co, or Ni) for pursuing a well-controllable morphology and an excellent activity by taking advantage of its more stable nature at high temperature and in acidic or alkaline electrolyte. It is discovered that metallic Cu exhibits strong electronic modulation on N-doped carbon to boost its electrocatalytic activity for HER. Such a nanostructure not only offers plenty of accessible highly active sites but also provides a 3D conductive open network for fast electron/mass transfer and facilitates gas escape for prompt mass exchange. As a result, the Cu@NC NT/CF electrode exhibits superior HER performance and durability, outperforming most of the reported M@NC materials. Furthermore, the etching experiments together with X-ray photoelectron spectroscopy (XPS) analysis reveal that the electronic modulation from encased Cu significantly enhances the HER activity of N-doped carbon. These findings open up opportunities for exploring other Cu-based nanomaterials as efficient electrocatalysts and understanding their catalytic processes.

Magnetic, recyclable PtyCo1−y/Ti3C2X2 (X = O, F) catalyst: a facile synthesis and enhanced catalytic activity for hydrogen generation from the hydrolysis of ammonia borane

Exploring the applications of two dimensional layered Ti3C2X2 (X = OH, F) is of great importance because of its excellent physical and chemical properties. Herein, we report the synthesis of the bimetallic catalyst PtyCo1−y/Ti3C2X2via a facile one-pot approach using Ti3C2X2 as the support. The in situ synthesized PtyCo1−y/Ti3C2X2 is subsequently applied as a catalyst for hydrogen evolution from the hydrolysis of ammonia borane at 25 °C. Experimental results show that Pt0.08Co0.92/Ti3C2X2 exhibits excellent catalytic activity for the hydrolysis of ammonia borane with a high hydrogen generation rate of 100.7 L H2 (min gPt)−1 and turnover frequency of 727 mol H2 (min molPt)−1 because of the synergistic effect between Pt and Co. Moreover, Pt0.08Co0.92/Ti3C2X2 could be recovered from the reaction mixture by a magnet and recycled at least seven times, thus showing its high recycling efficiency.

Tunable magnetic pole inversion in multiferroic BiFeO3–DyFeO3 solid solution

In ferromagnets, the magnetic moment can generally be reversed by applying a sufficiently high external magnetic field of opposite polarity. Temperature, on the other hand, is usually known to affect only the magnitude of a magnetic moment, rather than its sign or polarity (most magnets exhibit a monotonic increase in magnetization upon cooling below their magnetic phase transition temperature). As a result, temperature-induced magnetization reversal (i.e. magnetic pole inversion) remains a very rare phenomenon which lacks proper understanding and explanation because of the extreme difficulties encountered in controlling the thermodynamics of magnetization of classical metal or metal oxide magnets. Herein, we report an unusual magnetic pole inversion behaviour in multiferroic (1 − x)BiFeO3–xDyFeO3 solid solution (alloy), which can be tuned by varying the concentration of the magnetic ion Dy3+ in the solid solution. It is found that the temperature-induced magnetic pole inversion occurs in a wide composition range (x = 0.14–0.90). Moreover, for the first time in any ferrites, multiple magnetic pole inversions are observed in the solid solution compounds of high Dy3+-concentrations. Our results may provide a better understanding of the temperature- and composition-induced magnetic pole inversion and related phenomena and point to new potential applications for magnetic and multiferroic materials.

Facile synthesis of effective Ru nanoparticles on carbon by adsorption-low temperature pyrolysis strategy for hydrogen evolution

The facile synthesis of efficient catalysts for hydrogen evolution from electrochemical water splitting and ammonia borane (AB) hydrolysis is highly important. Here, we develop an adsorption-low temperature pyrolysis method for facilely preparing uniformly dispersed Ru nanoparticles on carbon (Ru/C) with an outstanding catalytic property toward hydrogen generation from both electrochemical water splitting and AB hydrolysis. The experimental results indicate that the Ru/C synthesized by calcination at 300 °C (Ru/C-300) exhibits the highest catalytic activity for the hydrogen evolution reaction (HER) in basic solution, which requires an overpotential of only 14 mV at 10 mA cm−2. Additionally, this catalyst also displays high activity and reusability toward hydrogen evolution through AB hydrolysis, leading to a high turnover frequency of 643 mol H2 (min molRu)−1. Moreover, the Ru/C-300 shows excellent stability and reusability for both reactions. The adsorption-low temperature calcination strategy ensures that the small Ru nanoparticles are confined onto the carbon matrix, which can provide abundant highly reactive surface sites. It is discovered that the excellent catalytic activity of Ru/C depends largely on the size and dispersion of Ru nanoparticles as well as on their chemical states. This work may provide a facile and environmentally friendly strategy for preparing uniformly distributed metal nanocatalysts with high catalytic efficiencies for HER and AB hydrolysis.

Size and Electronic Modulation of Iridium Nanoparticles on Nitrogen Functionalized Carbon toward Advanced Electrocatalysts for Alkaline Water Splitting

Developing efficient catalytic materials for electrochemical water splitting is important. Herein, uniformly dispersed and size-controllable iridium (Ir) nanoparticles (NPs) were prepared using a nitrogen-functionalized carbon as the support (Ir/CN). We found that nitrogen functionalization can simultaneously modulate the size of Ir NPs to substantially enhance the catalytically active sites and adjust the electronic structure of Ir, thereby promoting electrocatalytic activity for water splitting. Consequently, the as-synthesized Ir/CN shows excellent electrocatalytic performance with overpotentials of 12 and 265 mV for hydrogen and oxygen evolution reactions in basic medium, respectively. These findings may pave the way for designing and synthesizing other similar materials as efficient catalysts for electrochemical water splitting.

Self-supported 3D Nanoporous Ni/V2O3 Hybrid Nanoplate Assemblies for Highly Efficient Electrochemical Hydrogen Evolution

Nickel-based non-noble-metal materials have emerged as promising catalysts for electrochemical hydrogen production in view of their attractive intrinsic activities, electrical properties and low cost. Exploring new candidates for further improving the performances of nickel-based catalysts and understanding the structure–activity relationship are still necessary to reduce the overpotential of the hydrogen evolution reaction (HER) thus advancing their application in electrochemical water splitting. Herein, we developed a facile two-step self-templated strategy for fabricating a three-dimensional (3D) nanoporous nickel/vanadium oxide (Ni/V2O3) nanoplate assembly as a new efficient catalyst for alkaline HER. It is found that by controllably annealing the Ni–V–O assembly as a single precursor, Ni and V2O3 components are uniformly integrated in the nanoporous composite, showing a synergistically enhancing effect on the HER. The resulting 3D nanoporous structure not only creates numerous active sites accessible for the HER but also provides a conductive open network towards efficient electron/mass transport. Consequently, the nanoporous Ni/V2O3 nanoplate assembly exhibits excellent catalytic performance for alkaline HER in terms of a low overpotential of 61 mV at 10 mA cm−2 and a small Tafel slope of 79.7 mV dec−1 together with excellent long-term durability. These findings provide new insights into good design and construction of other highly active catalysts for diverse applications.

Towards High-Efficiency Hydrogen Production through in situ Formation of Well-Dispersed Rhodium Nanoclusters

Rhodium (Rh)-based materials have been emerged as potential candidates for hydrogen revolution from electrolyzing water or ammonia borane (AB) hydrolysis. Nevertheless, most of the catalysts still suffer from the complex synthetic procedures combined with limited catalytic activity. Additionally, the facile syntheses of Rh catalysts with high efficiencies for both electrochemical water splitting and AB hydrolysis are still challenging. Herein, we develop a simple, green and mass-producible ion-adsorption strategy to produce Rh/C pre-catalyst. The ultrafine and clean Rh nanoclusters immobilized on carbon (in situ-Rh/C) is achieved via the in-situ reduction of the Rh/C pre-catalyst during the hydrogen evolution processes. The in situRh/C catalyst presents an outstanding electrocatalytic performance with low overpotentials of 8 and 30 mV at 10 mA cm current density in 1.0 M KOH and 0.5 M H2SO4, respectively, outperforming the stateof-the-art Pt catalysts. Furthermore, the in situ-Rh/C is also highly active for AB hydrolysis to produce hydrogen with a high turnover frequency of 1246 mol H2 (molRh min) −1 at 25 °C. The in situ formed ultrafine Rh nanoclusters during the hydrogen generation process are responsible for the observed superior catalytic performance. The facile and feasible strategy to realize highly active catalyst shows premise in practical applications.Rh-based materials have emerged as potential candidates for hydrogen revolution from electrolyzing water or ammonia borane (AB) hydrolysis. Nevertheless, most of the catalysts still suffer from the complex synthetic procedures combined with limited catalytic activity. Additionally, the facile syntheses of Rh catalysts with high efficiencies for both electrochemical water splitting and AB hydrolysis are still challenging. Herein, we develop a simple, green, and mass-producible ion-adsorption strategy to produce a Rh/C pre-catalyst (pre-Rh/C). The ultrafine and clean Rh nanoclusters immobilized on carbon are achieved via the inu2005situ reduction of the pre-Rh/C during the hydrogen-evolution process. The resulting inu2005situ Rh/C catalyst presents an outstanding electrocatalytic performance with low overpotentials of 8 and 30u2005mV at 10u2005mAu2009cm-2 in 1.0u2009m KOH and 0.5u2009m H2 SO4 , respectively, outperforming the state-of-the-art Pt catalysts. Furthermore, the inu2005situ Rh/C is also highly active for AB hydrolysis to produce hydrogen with a high turnover frequency of 1246u2005mol H2 u2009molRh-1 u2009min-1 at 25u2009°C. The inu2005situ-formed ultrafine Rh nanoclusters are responsible for the observed superior catalytic performance. This facile inu2005situ strategy to realize a highly active catalyst shows promise for practical applications.