Surface Roughed and Pt-Rich Bimetallic Electrocatalysts for Hydrogen Evolution Reaction.
ABSTRACT: Platinum-based alloys with low cost transition metals have been considered as promising electrocatalysts in the field of sustainable energy conversion and storage. Herein, chloroplatinic acid, cobalt chloride, and carbon nanotubes are used as platinum, cobalt precursors, and carriers, respectively, to prepare rich Pt dealloying PtCo nanoparticles (SD-PtCo/CNT) via co-liquid phase reduction and chemical dealloying methods. The characterization and test results confirm that PtCo alloy nanoparticles are evenly dispersed on carbon nanotubes, further dealloying and resulting in the partial dissolving of cobalt, simultaneously generating a rich Pt layer and roughly active surface. Benefiting from the unique structure, the SD-PtCo/CNT catalyst displays obviously enhanced HER activity in both acidic and alkaline conditions. In 1.0 M KOH, SD-PtCo/CNT exhibits a low overpotential of 78 mV at 10 mA/cm2 and a small tafel slope (38.28 mV/dec). In 0.5 M H2SO4, SD-PtCo/CNT still shows the superior performance compared with un-dealloying PtCo/CNT, with an overpotential of 17 mV at 10 mA/cm2 and corresponding tafel slope of 21.35 mV/dec. The high HER activity of SD-PtCo/CNT can be attributed to the formation of a platinum rich layer and the uniformly dispersed PtCo nanoparticles supported on superior conductive carbon nanotubes, suggesting its great potential for hydrogen generation via water splitting.
Project description:Designing highly active and robust platinum-free catalysts for hydrogen evolution reaction is of vital importance for clean energy applications yet challenging. Here we report highly active and stable cobalt-substituted ruthenium nanosheets for hydrogen evolution, in which cobalt atoms are isolated in ruthenium lattice as revealed by aberration-corrected high-resolution transmission electron microscopy and X-ray absorption fine structure measurement. Impressively, the cobalt-substituted ruthenium nanosheets only need an extremely low overpotential of 13?mV to achieve a current density of 10?mA?cm-2 in 1?M KOH media and an ultralow Tafel slope of 29?mV dec-1, which exhibit top-level catalytic activity among all reported platinum-free electrocatalysts. The theoretical calculations reveal that the energy barrier of water dissociation can greatly reduce after single cobalt atom substitution, leading to its superior hydrogen evolution performance. This study provides a new insight into the development of highly efficient platinum-free hydrogen evolution catalysts.
Project description:Electrochemical water splitting in alkaline media plays an important role in mass production of hydrogen. Ruthenium (Ru), as the cheapest member of platinum-group metals, has attracted much attention, and the incorporation of trace amount of Ru with cobalt phosphide could significantly improve the hydrogen evolution reaction (HER) catalytic activity. In this work, ruthenium-incorporated cobalt phosphide nanocubes are synthesized via a reaction between Co-Co Prussian blue analog (Co-PBA) and ruthenium chloride (RuCl<sub>3</sub>) followed by the phosphidation. The sample with a Ru content of ~2.04 wt.% exhibits the best HER catalytic activity with a low overpotential of 51 and 155 mV, to achieve the current densities of -10 and -100 mA cm<sup>-2</sup>, respectively, and the Tafel slope of 53.8 mV dec<sup>-1</sup>, which is comparable to the commercial Pt/C. This study provides a new perspective to the design and construction of high performance electrocatalysts for HER and other catalytic applications in a relatively low price.
Project description:Various platinum-free electrocatalysts have been explored for hydrogen evolution reaction in acidic solutions. However, in economical water-alkali electrolysers, sluggish water dissociation kinetics (Volmer step) on platinum-free electrocatalysts results in poor hydrogen-production activities. Here we report a MoNi4 electrocatalyst supported by MoO2 cuboids on nickel foam (MoNi4/MoO2@Ni), which is constructed by controlling the outward diffusion of nickel atoms on annealing precursor NiMoO4 cuboids on nickel foam. Experimental and theoretical results confirm that a rapid Tafel-step-decided hydrogen evolution proceeds on MoNi4 electrocatalyst. As a result, the MoNi4 electrocatalyst exhibits zero onset overpotential, an overpotential of 15?mV at 10?mA?cm-2 and a low Tafel slope of 30?mV per decade in 1?M potassium hydroxide electrolyte, which are comparable to the results for platinum and superior to those for state-of-the-art platinum-free electrocatalysts. Benefiting from its scalable preparation and stability, the MoNi4 electrocatalyst is promising for practical water-alkali electrolysers.
Project description:Electrolysis of water to produce hydrogen is crucial for developing sustainable clean energy and protecting the environment. However, because of the multi-electron transfer in the oxygen evolution reaction (OER) process, the kinetics of the reaction is seriously hindered. To address this issue, we designed and synthesized hollow CoP/FeP<sub>4</sub> heterostructural nanorods interwoven by carbon nanotubes (CoP/FeP<sub>4</sub>@CNT) via a hydrothermal reaction and a phosphorization process. The CoP/FeP<sub>4</sub>@CNT hybrid catalyst delivers prominent OER electrochemical performances: it displays a substantially smaller Tafel slope of 48.0 mV dec<sup>-1</sup> and a lower overpotential of 301 mV at 10 mA cm<sup>-2</sup>, compared with an RuO<sub>2</sub> commercial catalyst; it also shows good stability over 20 h. The outstanding OER property is mainly attributed to the synergistic coupling between its unique CNT-interwoven hollow nanorod structure and the CoP/FeP<sub>4</sub> heterojunction, which can not only guarantee high conductivity and rich active sites, but also greatly facilitate the electron transfer, ion diffusion, and O<sub>2</sub> gas release and significantly enhance its electrocatalytic activity. This work offers a facile method to develop transition metal-based phosphide heterostructure electrocatalysts with a unique hierarchical nanostructure for high performance water oxidation.
Project description:This study reports a detailed analysis of an electrode material containing poly(phenolphthalein), carbon nanotubes and gold nanoparticles which shows superior catalytic effect towards to hydrazine oxidation in Britton-Robinson buffer (pH 10.0). Glassy carbon electrode was modified by electropolymerization of phenolphthalein (PP) monomer (poly(PP)/GCE) and the multiwalled carbon nanotubes (MWCNTs) was dropped on the surface. This modified surface was electrodeposited with gold nanoparticles (AuNPs/CNT/poly(PP)/GCE). The fabricated electrode was analysed the determination of hydrazine using cyclic voltammetry, linear sweep voltammetry and amperometry. The peak potential of hydrazine oxidation on bare GCE, poly(PP)/GCE, CNT/GCE, CNT/poly(PP)/GCE, and AuNPs/CNT/poly(PP)/GCE were observed at 596 mV, 342 mV, 320 mV, 313 mV, and 27 mV, respectively. A shift in the overpotential to more negative direction and an enhancement in the peak current indicated that the AuNPs/CNT/poly(PP)/GC electrode presented an efficient electrocatalytic activity toward oxidation of hydrazine. Modified electrodes were characterized with High-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Amperometric current responses in the low hydrazine concentration range of 0.25-13 µM at the AuNPs/CNT/poly(PP)/GCE. The limit of detection (LOD) value was obtained to be 0.083 µM. A modified electrode was applied to naturel samples for hydrazine determination.
Project description:The electroreduction of water for sustainable hydrogen production is a critical component of several developing clean-energy technologies, such as water splitting and fuel cells. However, finding a cheap and efficient alternative catalyst to replace currently used platinum-based catalysts is still a prerequisite for the commercialization of these technologies. Here we report a robust and highly active catalyst for hydrogen evolution reaction that is constructed by in situ growth of molybdenum disulfide on the surface of cobalt diselenide. In acidic media, the molybdenum disulfide/cobalt diselenide catalyst exhibits fast hydrogen evolution kinetics with onset potential of -11?mV and Tafel slope of 36?mV per decade, which is the best among the non-noble metal hydrogen evolution catalysts and even approaches to the commercial platinum/carbon catalyst. The high hydrogen evolution activity of molybdenum disulfide/cobalt diselenide hybrid is likely due to the electrocatalytic synergistic effects between hydrogen evolution-active molybdenum disulfide and cobalt diselenide materials and the much increased catalytic sites.
Project description:Promoting the intrinsic activity and accessibility of basal plane sites in 2D layered metal dichalcogenides is desirable to optimize their catalytic performance for energy conversion and storage. Herein, a core/shell structured hybrid catalyst, which features few-layered ruthenium (Ru)-doped molybdenum disulfide (MoS2) nanosheets closely sheathing around multiwalled carbon nanotube (CNT), for highly efficient hydrogen evolution reaction (HER) is reported. With 5 at% (atomic percent) Ru substituting for Mo in MoS2, Ru-MoS2/CNT achieves the optimum HER activity, which displays a small overpotential of 50 mV at -10 mA cm-2 and a low Tafel slope of 62 mV dec-1 in 1 m KOH. Theoretical simulations reveal that Ru substituting for Mo in coordination with six S atoms is thermodynamically stable, and the in-plane S atoms neighboring Ru dopants represent new active centers for facilitating water adsorption, dissociation, and hydrogen adsorption/desorption. This work provides a multiscale structural and electronic engineering strategy for synergistically enhancing the HER activity of transition metal dichalcogenides.
Project description:Layered double hydroxides (LDH) are being used as electrocatalysts for oxygen evolution reactions (OERs). However, low current densities limit their practical applications. Herein, we report a facile and economic synthesis of an iron-copper based LDH integrated with a cobalt-based metal-organic framework (ZIF-12) to form LDH-ZIF-12 composite (1) through a co-precipitation method. The as-synthesized composite <b>1</b> requires a low overpotential of 337 mV to achieve a catalytic current density of 10 mA cm<sup>-2</sup> with a Tafel slope of 89 mV dec<sup>-1</sup>. Tafel analysis further demonstrates that <b>1</b> exhibits a slope of 89 mV dec<sup>-1</sup> which is much lower than the slope of 284 mV dec<sup>-1</sup> for LDH and 172 mV dec<sup>-1</sup> for ZIF-12. The slope value of <b>1</b> is also lower than previously reported electrocatalysts, including Ni-Co LDH (113 mV dec<sup>-1</sup>) and Zn-Co LDH nanosheets (101 mV dec<sup>-1</sup>), under similar conditions. Controlled potential electrolysis and stability test experiments show the potential application of <b>1</b> as a heterogeneous electrocatalyst for water oxidation.
Project description:Single atom catalyst, which contains isolated metal atoms singly dispersed on supports, has great potential for achieving high activity and selectivity in hetero-catalysis and electrocatalysis. However, the activity and stability of single atoms and their interaction with support still remains a mystery. Here we show a stable single atomic ruthenium catalyst anchoring on the surface of cobalt iron layered double hydroxides, which possesses a strong electronic coupling between ruthenium and layered double hydroxides. With 0.45 wt.% ruthenium loading, the catalyst exhibits outstanding activity with overpotential 198?mV at the current density of 10?mA?cm<sup>-2</sup> and a small Tafel slope of 39?mV?dec<sup>-1</sup> for oxygen evolution reaction. By using operando X-ray absorption spectroscopy, it is disclosed that the isolated single atom ruthenium was kept under the oxidation states of 4+ even at high overpotential due to synergetic electron coupling, which endow exceptional electrocatalytic activity and stability simultaneously.
Project description:Water electrolysis is an emerging energy conversion technology, which is significant for efficient hydrogen (H<sub>2</sub>) production. Based on the high-activity transition metal ions and metal alloys of ultrastable bifunctional catalyst, the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are the key to achieving the energy conversion method by overall water splitting (OWS). This study reports that the Co-based coordination polymer (ZIF-67) anchoring on an indium-organic framework (InOF-1) composite (InOF-1@ZIF-67) is treated followed by carbonization and phosphorization to successfully obtain CoP nanoparticles-embedded carbon nanotubes and nitrogen-doped carbon materials (CoP-InNC@CNT). As HER and OER electrocatalysts, it is demonstrated that CoP-InNC@CNT simultaneously exhibit high HER performance (overpotential of 153 mV in 0.5 m H<sub>2</sub>SO<sub>4</sub> and 159 mV in 1.0 m KOH) and OER performance (overpotential of 270 mV in 1.0 m KOH) activities to reach the current density of 10 mA cm<sup>-2</sup>. In addition, these CoP-InNC@CNT rods, as a cathode and an anode, can display an excellent OWS performance with ?<sub>10</sub> = 1.58 V and better stability, which shows the satisfying electrocatalyst for the OWS compared to control materials. This method ensures the tight and uniform growth of the fast nucleating and stable materials on substrate and can be further applied for practical electrochemical reactions.