Co-reporter:Bo You, Xuan Liu, Guoxiang Hu, Sheraz Gul, Junko Yano, De-en Jiang, and Yujie Sun
Journal of the American Chemical Society September 6, 2017 Volume 139(Issue 35) pp:12283-12283
Publication Date(Web):August 10, 2017
DOI:10.1021/jacs.7b06434
The development of low-cost hybrid water splitting–biosynthetic systems that mimic natural photosynthesis to achieve solar-to-chemical conversion is of great promise for future energy demands, but often limited by the kinetically sluggish hydrogen evolution reaction (HER) on the surface of nonprecious transition metal catalysts in neutral media. It is thus highly desirable to rationally tailor the reaction interface to boost the neutral HER catalytic kinetics. Herein, we report a general surface nitrogen modification of diverse transition metals (e.g., iron, cobalt, nickel, copper, and nickel–cobalt alloy), accomplished by a facile low-temperature ammonium carbonate treatment, for significantly improved hydrogen generation from neutral water. Various physicochemical characterization techniques including synchrotron X-ray absorption spectroscopy (XAS) and theory modeling demonstrate that the surface nitrogen modification does not change the chemical composition of the underlying transition metals. Notably, the resulting nitrogen-modified nickel framework (N–Ni) exhibits an extremely low overpotential of 64 mV at 10 mA cm–2, which is, to our knowledge, the best among those nonprecious electrocatalysts reported for hydrogen evolution at pH 7. Our combined experimental results and density functional theory (DFT) calculations reveal that the surface electron-rich nitrogen simultaneously facilitates the initial adsorption of water via the electron-deficient H atom and the subsequent dissociation of the electron-rich HO–H bond via H transfer to N on the nickel surface, beneficial to the overall hydrogen evolution process.
Co-reporter:Xuan Liu, Bo You, and Yujie Sun
ACS Sustainable Chemistry & Engineering June 5, 2017 Volume 5(Issue 6) pp:4778-4778
Publication Date(Web):April 11, 2017
DOI:10.1021/acssuschemeng.7b00182
Competent and low-cost electrocatalysts play a crucial role in the wide deployment of electrocatalytic water splitting for clean H2 production. Herein, for the first time, we report that readily available stainless steel can be transformed to competent electrocatalysts for both H2 and O2 evolution reactions (HER and OER, respectively) after facile surface modification. Specifically, our sulfurized stainless steel foil (SSFS) could achieve a catalytic current density of 10 mA cm–2 at overpotentials of 136 and 262 mV for HER and OER, respectively, in 1.0 M KOH. When SSFS served as the electrocatalysts for both the cathode and the anode, an overall water splitting current density of 10 mA cm–2 was obtained at 1.64 V with robust durability. Such a superior performance can rival those of many recently reported water splitting catalysts that consist of expensive elements, contain high-cost supports, or require sophisticated synthesis. In addition, excellent water splitting activity was also achieved by SSFS in neutral media, largely expanding its working conditions. Finally, we further demonstrated that analogous phosphorization and nitridation treatments also could substantially enhance the electrocatalytic performance of stainless steel for water splitting, suggesting the great versatility of our surface modification strategy.Keywords: Electrocatalysis; Stainless steel; Surface modification; Water splitting;
Co-reporter:Bo You, Xuan Liu, Xin Liu, and Yujie Sun
ACS Catalysis July 7, 2017 Volume 7(Issue 7) pp:4564-4564
Publication Date(Web):May 30, 2017
DOI:10.1021/acscatal.7b00876
Water electrolysis to produce H2 and O2 with renewable energy input has been generally viewed as an attractive route to meet future global energy demands. However, the sluggish O2 evolution reaction usually requires high overpotential and may yield reactive oxygen species (ROS) that can degrade the electrolyzer membrane and hence shorten the device lifetime. In addition, the potential gas crossover may result in an explosive H2/O2 mixture and hence safety risks. To address these issues, we herein report a general electrolysis strategy for the simultaneous H2 production and alcohol oxidative upgrading (e.g., benzyl alcohol, 4-nitrobenzyl alcohol, 4-methylbenzyl alcohol, ethanol, and 5-hydroxymethylfurfural), in which the thermodynamics of the latter is much easier than that of water oxidation. A facile and environmentally friendly template-free electrodeposition was used to obtain a 3D hierarchically porous nickel-based electrocatalyst (hp-Ni) for such an integrated electrolysis, requiring a voltage of ∼220 mV smaller than that of water splitting to achieve 50 mA cm–2 together with robust stability, high Faradaic efficiencies, and no formation of ROS, as well as production of valuable products at both the cathode (H2) and anode (alcohol oxidation products). More importantly, we demonstrated that these diverse alcohol oxidations over hp-Ni exhibited similar onset potentials which were largely determined by the desirable oxidation potential of hp-Ni, irrespective of the different intrinsic thermodynamics of these alcohol oxidation reactions. This result provides a new direction for the rational design of heterogeneous transition-metal-based electrocatalysts with lower oxidation potential for more highly efficient electrocatalytic alcohol oxidation.Keywords: alcohol oxidation; electrocatalysis; hydrogen evolution; nickel; water splitting;
Co-reporter:Bo You
Advanced Energy Materials 2016 Volume 6( Issue 7) pp:
Publication Date(Web):
DOI:10.1002/aenm.201502333
Co-reporter:Bo You, Xuan Liu, Nan Jiang, and Yujie Sun
Journal of the American Chemical Society 2016 Volume 138(Issue 41) pp:13639-13646
Publication Date(Web):September 21, 2016
DOI:10.1021/jacs.6b07127
Conventional water electrolyzers produce H2 and O2 simultaneously, such that additional gas separation steps are needed to prevent H2/O2 mixing. The sluggish anodic O2 evolution reaction (OER) always results in low overall energy conversion efficiency and the product of OER, O2, is not of significant value. In addition, the potential formation of reactive oxygen species (ROS) may lead to degradation of cell membranes and thus premature device failure. Herein we report a general concept of integrating oxidative biomass upgrading reactions with decoupled H2 generation from water splitting. Five representative biomass substrates, ethanol, benzyl alcohol, furfural, furfuryl alcohol, and 5-hydroxymethylfurfural (HMF), were selected for oxidative upgrading catalyzed by a hierarchically porous Ni3S2/Ni foam bifunctional electrocatalyst (Ni3S2/NF). All the five organics can be oxidized to value-added liquid products at much lower overpotentials than that of OER. In particular, the electrocatalytic oxidation of HMF to the value-added 2,5-furandicarboxylic acid (FDCA) was further studied in detail. Benefiting from the more favorable thermodynamics of HMF oxidation than that of OER, the cell voltage for integrated H2 production and HMF oxidation was significantly reduced by ∼200 mV relative to pure water splitting to achieve 100 mA cm–2, while the oxidation product (FDCA) at the anode was much more valuable than O2. When utilized as electrocatalysts for both cathode and anode, Ni3S2/NF demonstrated outstanding durability and nearly unity Faradaic efficiencies for both H2 and FDCA production. Overall, such an integration of oxidative biomass valorization and HER via earth-abundant electrocatalysts not only avoids the generation of explosive H2/O2 mixture and ROS, but also yields products of high value at both electrodes with lower voltage input, maximizing the energy conversion efficiency.
Co-reporter:Bo You, Nan Jiang, Meili Sheng, Margaret Winona Bhushan, and Yujie Sun
ACS Catalysis 2016 Volume 6(Issue 2) pp:714
Publication Date(Web):December 21, 2015
DOI:10.1021/acscatal.5b02193
The development of high-performance nonprecious electrocatalysts with both H2 and O2 evolution reaction (HER and OER) activities for overall water splitting is highly desirable but remains a grand challenge. Herein, we report a facile two-step method to synthesize three-dimensional hierarchically porous urchin-like Ni2P microsphere superstructures anchored on nickel foam (Ni2P/Ni/NF) as bifunctional electrocatalysts for overall water splitting. The Ni2P/Ni/NF catalysts were prepared by template-free electrodeposition of porous nickel microspheres on nickel foam followed by phosphidation. The hierarchically macroporous superstructures with 3D configuration can reduce ion transport resistance and facilitate the diffusion of gaseous products (H2 and O2). The optimal Ni2P/Ni/NF exhibited remarkable catalytic performance and outstanding stability for both the HER and OER in alkaline electrolyte (1.0 M KOH). For the HER, Ni2P/Ni/NF afforded a current density of 10 mA cm–2 at a low overpotential of only −98 mV. When it served as an OER electrocatalyst, Ni2P/Ni/NF was partially oxidized to nickel oxides/hydroxides/oxyhydroxides (mainly NiO) on the catalyst surface and exhibited excellent OER activity with small overpotentials of 200 and 268 mV to reach 10 and 100 mA cm–2, respectively. Furthermore, when Ni2P/Ni/NF was employed as the electrocatalyst for both the cathode and anode, a water splitting electrolyzer was able to reach 10 and 100 mA cm–2 in 1.0 M KOH at cell voltages of 1.49 and 1.68 V, respectively, together with robust durability. Various characterization techniques and controlled experiments indicated that the superior activity and strong stability of Ni2P/Ni/NF for overall water splitting originated from its electrochemically active constituents, 3D interconnected porosity, and high conductivity.Keywords: electrocatalysis; hydrogen evolution; nickel phosphide; oxygen evolution; superstructure; water splitting
Co-reporter:Xuan Liu, Bo You, Xin-Yao Yu, Jeffrey Chipman and Yujie Sun
Journal of Materials Chemistry A 2016 vol. 4(Issue 30) pp:11611-11615
Publication Date(Web):28 Jun 2016
DOI:10.1039/C6TA04289A
Supercapacitors have been widely recognized as a promising device for the storage of renewable energy. Herein, a facile electrochemical oxidation strategy is described to construct a nickel sulfide/oxide heterostructure which enhances the specific areal capacitance of Ni3S2 electrodeposited on nickel foam. The resulting heterostructure electrode exhibits high areal capacitance, 65 times that of the as-prepared Ni3S2 electrode (2035 mF cm−2vs. 31 mF cm−2 at a current density of 8 mA cm−2), while still maintaining great stability, showing no performance degradation after 5000 charge–discharge cycles. Its exceptional capacitance, advanced rate capability, and superior cycling stability are attributed to the transformed composition and unique nanostructure achieved during electrochemical oxidation, which can provide a large electrochemically active surface area, fast electron/electrolyte ion transport, and robust structural stability. Such a low-cost and facile strategy can be potentially applicable to prepare many other materials for supercapacitor applications.
Co-reporter:Nan Jiang, Qing Tang, Meili Sheng, Bo You, De-en Jiang and Yujie Sun
Catalysis Science & Technology 2016 vol. 6(Issue 4) pp:1077-1084
Publication Date(Web):22 Sep 2015
DOI:10.1039/C5CY01111F
Electrocatalytic water splitting to produce H2 plays an important role in the capture, conversion, and storage of renewable energy sources, such as solar energy and wind power. As the reductive half reaction of water splitting, H2 evolution reaction (HER) suffers from sluggish kinetics, and hence competent HER catalysts are needed. Despite being excellent HER catalysts, noble metal-based catalysts (i.e. Pt) are too expensive to be economically competitive. Therefore, low-cost catalysts composed of solely earth-abundant elements have attracted increasing attention these years, among which nickel-based HER catalysts, particularly nickel chalcogenides, are considered as promising candidates. Although many nickel chalcogenides, including NiS, NiS2, and Ni3S2, have been reported for hydrogen evolution, their intrinsic catalytic activities have never been investigated and compared in detail under the same conditions. Most of the previous investigations were limited to only one species of nickel chalcogenides under very unique conditions, rendering a fair comparison of their HER activities impossible. Herein, we report the preparation and characterization of three crystalline nickel sulfides, NiS, NiS2, and Ni3S2, with comparable crystal sizes and specific surface areas. Detailed electrochemical studies under strongly alkaline conditions coupled with theoretical computations were performed to probe their intrinsic HER activities, resulting in the order of Ni3S2 > NiS2 > NiS. The superior HER performance of Ni3S2 mainly stems from the combined effect of large electrochemically active surface area and high conductivity (metallic conductor vs. semiconductor).
Co-reporter:Nan Jiang;Dr. Bo You;Meili Sheng ;Dr. Yujie Sun
ChemCatChem 2016 Volume 8( Issue 1) pp:106-112
Publication Date(Web):
DOI:10.1002/cctc.201501150
Abstract
Efficient, stable, and low-cost electrocatalysts are crucial for realizing large-scale water splitting. Herein, we report that electrodeposited nickel–phosphorous (Ni–P) films can act as efficient bifunctional electrocatalysts for overall water splitting. The as-prepared Ni–P films exhibit remarkable catalytic performance for both H2 and O2 evolution reactions (HER and OER) in alkaline media, achieving a current density of 10 mA cm−2 at overpotentials of −93 mV for HER and 344 mV for OER with Tafel slopes of 43 and 49 mV dec−1, respectively, rivaling the performance of Pt and IrO2. Various techniques were employed to probe the composition and morphology of the Ni–P films prior to and post catalysis, revealing the major composition of the as-prepared and post-HER films as metallic nickel and nickel phosphide, which partially transform to nickel oxides during OER. It was also found that the catalytic rate of OER catalyzed by Ni–P was first order in the activity of the hydroxide anion.
Co-reporter:Nan Jiang;Dr. Bo You;Meili Sheng ;Dr. Yujie Sun
ChemCatChem 2016 Volume 8( Issue 1) pp:
Publication Date(Web):
DOI:10.1002/cctc.201501374
Co-reporter:Nan Jiang, Bo You, Raquel Boonstra, Irina M. Terrero Rodriguez, and Yujie Sun
ACS Energy Letters 2016 Volume 1(Issue 2) pp:386
Publication Date(Web):July 18, 2016
DOI:10.1021/acsenergylett.6b00214
Electrocatalytic biomass valorization with renewable energy input represents a promising way to produce sustainable and nonfossil-based carbon products. Even more desirable is that the oxidative biomass upgrading can be integrated with H2 production in a single electrolyzer. Herein, we report that electrodeposited Co–P can act as competent electrocatalysts for 5-hydroxymethylfurfural (HMF) oxidation to 2,5-furandicarboxylic acid (FDCA) at the anode and H2 production at the cathode simultaneously in alkaline media. When serving as a catalyst precursor on the anode, Co–P was able to achieve a current density of 20 mA/cm2 for HMF oxidation in 1.0 M KOH with 50 mM HMF at 1.38 V vs RHE, prior to the takeoff of the competing reaction, O2 evolution. Long-term chronoamperometry demonstrated a nearly 100% conversation of HMF and a ∼90% yield of FDCA. When HMF oxidation and H2 evolution were integrated in one electrolyzer with a Co–P/Co–P catalyst couple, the potential required to achieve a current density of 20 mA/cm2 was 1.44 V, 150 mV lower than that of overall water splitting. Nearly unity Faradaic efficiency was obtained for H2 evolution. Overall, our results indicate that it is feasible to employ earth-abundant electrocatalyts to integrate H2 production and oxidative biomass upgrading with higher energy conversion efficiency than water splitting as well as to produce valuable products at both cathode and anode in a single electrolyzer.
Co-reporter:Bo You, Nan Jiang, Meili Sheng, Sheraz Gul, Junko Yano, and Yujie Sun
Chemistry of Materials 2015 Volume 27(Issue 22) pp:7636
Publication Date(Web):November 5, 2015
DOI:10.1021/acs.chemmater.5b02877
The design of active, robust, and nonprecious electrocatalysts with both H2 and O2 evolution reaction (HER and OER) activities for overall water splitting is highly desirable but remains a grand challenge. Herein, we report a facile two-step method to synthesize porous Co-P/NC nanopolyhedrons composed of CoPx (a mixture of CoP and Co2P) nanoparticles embedded in N-doped carbon matrices as electrocatalysts for overall water splitting. The Co-P/NC catalysts were prepared by direct carbonization of Co-based zeolitic imidazolate framework (ZIF-67) followed by phosphidation. Benefiting from the large specific surface area, controllable pore texture, and high nitrogen content of ZIF (a subclass of metal–organic frameworks), the optimal Co-P/NC showed high specific surface area of 183 m2 g–1 and large mesopores, and exhibited remarkable catalytic performance for both HER and OER in 1.0 M KOH, affording a current density of 10 mA cm–2 at low overpotentials of −154 mV for HER and 319 mV for OER, respectively. Furthermore, a Co-P/NC-based alkaline electrolyzer approached 165 mA cm–2 at 2.0 V, superior to that of Pt/IrO2 couple, along with strong stability. Various characterization techniques including X-ray absorption spectroscopy (XAS) revealed that the superior activity and strong stability of Co-P/NC originated from its 3D interconnected mesoporosity with high specific surface area, high conductivity, and synergistic effect of CoPx encapsulated within N-doped carbon matrices.
Co-reporter:Bo You, Nan Jiang, Meili Sheng, Walter S. Drisdell, Junko Yano, and Yujie Sun
ACS Catalysis 2015 Volume 5(Issue 12) pp:7068
Publication Date(Web):October 22, 2015
DOI:10.1021/acscatal.5b02325
The development of low-cost catalysts with oxygen reduction reaction (ORR) activity superior to that of Pt for fuel cells is highly desirable but remains challenging. Herein, we report a bimetal–organic framework (bi-MOF) self-adjusted synthesis of support-free porous Co–N–C nanopolyhedron electrocatalysts by pyrolysis of a Zn/Co bi-MOF without any post-treatments. The presence of initial Zn forms a spatial isolation of Co that suppresses its sintering during pyrolysis, and Zn evaporation also promotes the surface area of the resultant catalysts. The composition, morphology, and hence ORR activity of Co–N–C could be tuned by the Zn/Co ratio. The optimal Co–N–C exhibited remarkable ORR activity with a half-wave potential of 0.871 V versus the reversible hydrogen electrode (RHE) (30 mV more positive than that of commercial 20 wt % Pt/C) and a kinetic current density of 39.3 mA cm–2 at 0.80 V versus RHE (3.1 times that of Pt/C) in 0.1 M KOH, and excellent stability and methanol tolerance. It also demonstrated ORR activity comparable to and stability much higher than those of Pt/C in acidic and neutral electrolytes. Various characterization techniques, including X-ray absorption spectroscopy, revealed that the superior activity and strong stability of Co–N–C originated from the intense interaction between Co and N, the high content of ORR active pyridinic and pyrrolic N, and the large specific surface area.Keywords: electrocatalyst; metal−organic framework; nonprecious; oxygen reduction; self-adjusted
Co-reporter:Bo You, Nan Jiang, Meili Sheng and Yujie Sun
Chemical Communications 2015 vol. 51(Issue 20) pp:4252-4255
Publication Date(Web):26 Jan 2015
DOI:10.1039/C4CC09849H
Hollow cobalt sulfide nanoprisms obtained by a two-step, microwave-assisted synthesis within 15 min exhibit higher hydrogen evolution catalytic activity and better specific capacitance than their counterparts prepared by a traditional solvothermal method.
Co-reporter:Meili Sheng, Nan Jiang, Samantha Gustafson, Bo You, Daniel H. Ess and Yujie Sun
Dalton Transactions 2015 vol. 44(Issue 37) pp:16247-16250
Publication Date(Web):17 Aug 2015
DOI:10.1039/C5DT02916C
We report a planar nickel complex coordinated with a pincer-type carbene–pyridine–carbene ligand which exhibits high selectivity for electrocatalytic CO2 reduction in the presence of H2O.
Co-reporter:Nan Jiang;Dr. Bo You;Meili Sheng ;Dr. Yujie Sun
Angewandte Chemie 2015 Volume 127( Issue 21) pp:
Publication Date(Web):
DOI:10.1002/ange.201503447
Co-reporter:Nan Jiang;Dr. Bo You;Meili Sheng ;Dr. Yujie Sun
Angewandte Chemie 2015 Volume 127( Issue 21) pp:6349-6352
Publication Date(Web):
DOI:10.1002/ange.201501616
Abstract
One of the challenges to realize large-scale water splitting is the lack of active and low-cost electrocatalysts for its two half reactions: H2 and O2 evolution reactions (HER and OER). Herein, we report that cobalt-phosphorous-derived films (Co-P) can act as bifunctional catalysts for overall water splitting. The as-prepared Co-P films exhibited remarkable catalytic performance for both HER and OER in alkaline media, with a current density of 10 mA cm−2 at overpotentials of −94 mV for HER and 345 mV for OER and Tafel slopes of 42 and 47 mV/dec, respectively. They can be employed as catalysts on both anode and cathode for overall water splitting with 100 % Faradaic efficiency, rivalling the integrated performance of Pt and IrO2. The major composition of the as-prepared and post-HER films are metallic cobalt and cobalt phosphide, which partially evolved to cobalt oxide during OER.
Co-reporter:Nan Jiang;Dr. Bo You;Meili Sheng ;Dr. Yujie Sun
Angewandte Chemie International Edition 2015 Volume 54( Issue 21) pp:6251-6254
Publication Date(Web):
DOI:10.1002/anie.201501616
Abstract
One of the challenges to realize large-scale water splitting is the lack of active and low-cost electrocatalysts for its two half reactions: H2 and O2 evolution reactions (HER and OER). Herein, we report that cobalt-phosphorous-derived films (Co-P) can act as bifunctional catalysts for overall water splitting. The as-prepared Co-P films exhibited remarkable catalytic performance for both HER and OER in alkaline media, with a current density of 10 mA cm−2 at overpotentials of −94 mV for HER and 345 mV for OER and Tafel slopes of 42 and 47 mV/dec, respectively. They can be employed as catalysts on both anode and cathode for overall water splitting with 100 % Faradaic efficiency, rivalling the integrated performance of Pt and IrO2. The major composition of the as-prepared and post-HER films are metallic cobalt and cobalt phosphide, which partially evolved to cobalt oxide during OER.
Co-reporter:Nan Jiang;Dr. Bo You;Meili Sheng ;Dr. Yujie Sun
Angewandte Chemie International Edition 2015 Volume 54( Issue 21) pp:
Publication Date(Web):
DOI:10.1002/anie.201503447
Co-reporter:Nan Jiang, Lia Bogoev, Marina Popova, Sheraz Gul, Junko Yano and Yujie Sun
Journal of Materials Chemistry A 2014 vol. 2(Issue 45) pp:19407-19414
Publication Date(Web):17 Oct 2014
DOI:10.1039/C4TA04339A
The development of low-cost, efficient, and robust electrocatalysts of the hydrogen evolution reaction (HER) is a crucial step toward the conversion and storage of sustainable and carbon-neutral energy resources, such as solar energy. Not only the HER catalysts need to be composed of inexpensive elements, they are also desirable to be prepared at low energy cost. In this work, we report that nickel-sulfide (Ni-S) films prepared by facile potentiodynamic deposition are active HER catalysts in aqueous media. Notably, the Ni-S films showed catalytic activity in water with a wide range of pH values (0 to 14), as well as in natural water. In pH 7 phosphate buffer, a current density of 60 mA cm−2 could be achieved with a Tafel slope of 77 mV dec−1 and a Faradaic efficiency of 100%. A long-term bulk electrolysis of the Ni-S film exhibited steady current over 100 h with no deactivation, demonstrating its superior stability in neutral water. Further, an initial activation process was observed, which is likely due to the increase in the effective surface area of the Ni-S film under electrocatalytic conditions. A suite of characterization techniques, including X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, were conducted to probe the composition and structure of the Ni-S film, revealing that its major component is Ni3S2 which was preserved under electrocatalytic conditions.
Co-reporter:Nan Jiang, Lia Bogoev, Marina Popova, Sheraz Gul, Junko Yano and Yujie Sun
Journal of Materials Chemistry A 2014 - vol. 2(Issue 45) pp:NaN19414-19414
Publication Date(Web):2014/10/17
DOI:10.1039/C4TA04339A
The development of low-cost, efficient, and robust electrocatalysts of the hydrogen evolution reaction (HER) is a crucial step toward the conversion and storage of sustainable and carbon-neutral energy resources, such as solar energy. Not only the HER catalysts need to be composed of inexpensive elements, they are also desirable to be prepared at low energy cost. In this work, we report that nickel-sulfide (Ni-S) films prepared by facile potentiodynamic deposition are active HER catalysts in aqueous media. Notably, the Ni-S films showed catalytic activity in water with a wide range of pH values (0 to 14), as well as in natural water. In pH 7 phosphate buffer, a current density of 60 mA cm−2 could be achieved with a Tafel slope of 77 mV dec−1 and a Faradaic efficiency of 100%. A long-term bulk electrolysis of the Ni-S film exhibited steady current over 100 h with no deactivation, demonstrating its superior stability in neutral water. Further, an initial activation process was observed, which is likely due to the increase in the effective surface area of the Ni-S film under electrocatalytic conditions. A suite of characterization techniques, including X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, were conducted to probe the composition and structure of the Ni-S film, revealing that its major component is Ni3S2 which was preserved under electrocatalytic conditions.
Co-reporter:Bo You, Nan Jiang, Meili Sheng and Yujie Sun
Chemical Communications 2015 - vol. 51(Issue 20) pp:NaN4255-4255
Publication Date(Web):2015/01/26
DOI:10.1039/C4CC09849H
Hollow cobalt sulfide nanoprisms obtained by a two-step, microwave-assisted synthesis within 15 min exhibit higher hydrogen evolution catalytic activity and better specific capacitance than their counterparts prepared by a traditional solvothermal method.
Co-reporter:Xuan Liu, Bo You, Xin-Yao Yu, Jeffrey Chipman and Yujie Sun
Journal of Materials Chemistry A 2016 - vol. 4(Issue 30) pp:NaN11615-11615
Publication Date(Web):2016/06/28
DOI:10.1039/C6TA04289A
Supercapacitors have been widely recognized as a promising device for the storage of renewable energy. Herein, a facile electrochemical oxidation strategy is described to construct a nickel sulfide/oxide heterostructure which enhances the specific areal capacitance of Ni3S2 electrodeposited on nickel foam. The resulting heterostructure electrode exhibits high areal capacitance, 65 times that of the as-prepared Ni3S2 electrode (2035 mF cm−2vs. 31 mF cm−2 at a current density of 8 mA cm−2), while still maintaining great stability, showing no performance degradation after 5000 charge–discharge cycles. Its exceptional capacitance, advanced rate capability, and superior cycling stability are attributed to the transformed composition and unique nanostructure achieved during electrochemical oxidation, which can provide a large electrochemically active surface area, fast electron/electrolyte ion transport, and robust structural stability. Such a low-cost and facile strategy can be potentially applicable to prepare many other materials for supercapacitor applications.
Co-reporter:Meili Sheng, Nan Jiang, Samantha Gustafson, Bo You, Daniel H. Ess and Yujie Sun
Dalton Transactions 2015 - vol. 44(Issue 37) pp:NaN16250-16250
Publication Date(Web):2015/08/17
DOI:10.1039/C5DT02916C
We report a planar nickel complex coordinated with a pincer-type carbene–pyridine–carbene ligand which exhibits high selectivity for electrocatalytic CO2 reduction in the presence of H2O.
Co-reporter:Nan Jiang, Qing Tang, Meili Sheng, Bo You, De-en Jiang and Yujie Sun
Catalysis Science & Technology (2011-Present) 2016 - vol. 6(Issue 4) pp:NaN1084-1084
Publication Date(Web):2015/09/22
DOI:10.1039/C5CY01111F
Electrocatalytic water splitting to produce H2 plays an important role in the capture, conversion, and storage of renewable energy sources, such as solar energy and wind power. As the reductive half reaction of water splitting, H2 evolution reaction (HER) suffers from sluggish kinetics, and hence competent HER catalysts are needed. Despite being excellent HER catalysts, noble metal-based catalysts (i.e. Pt) are too expensive to be economically competitive. Therefore, low-cost catalysts composed of solely earth-abundant elements have attracted increasing attention these years, among which nickel-based HER catalysts, particularly nickel chalcogenides, are considered as promising candidates. Although many nickel chalcogenides, including NiS, NiS2, and Ni3S2, have been reported for hydrogen evolution, their intrinsic catalytic activities have never been investigated and compared in detail under the same conditions. Most of the previous investigations were limited to only one species of nickel chalcogenides under very unique conditions, rendering a fair comparison of their HER activities impossible. Herein, we report the preparation and characterization of three crystalline nickel sulfides, NiS, NiS2, and Ni3S2, with comparable crystal sizes and specific surface areas. Detailed electrochemical studies under strongly alkaline conditions coupled with theoretical computations were performed to probe their intrinsic HER activities, resulting in the order of Ni3S2 > NiS2 > NiS. The superior HER performance of Ni3S2 mainly stems from the combined effect of large electrochemically active surface area and high conductivity (metallic conductor vs. semiconductor).
Co-reporter:Bo You, Nan Jiang and Yujie Sun
Inorganic Chemistry Frontiers 2016 - vol. 3(Issue 2) pp:NaN285-285
Publication Date(Web):2015/12/07
DOI:10.1039/C5QI00196J
Transition metal chalcogenides such as cobalt sulfides (CoS) have recently attracted significant interest in electrocatalytic hydrogen evolution reaction (HER). In addition to the constituent elements and hence intrinsic activity, the morphology, porosity, and specific surface area of a nanostructured catalyst would substantially impact its overall electrocatalytic performance. In this paper, we report a facile and rapid two-step microwave-assisted anion-exchange route to prepare nanostructured CoS. By simply controlling the microwave sulfurization time, CoS of various morphologies such as hollow prisms, broken prisms, and nanoparticles could be obtained. Importantly, the correlation between morphology and HER activity of CoS in neutral water was systematically studied through a set of material characterization and electrochemical techniques. It's revealed that the morphology of CoS changed from hollow nanoprisms to 3D nanoparticles when increasing the microwave sulfurization time from 5 to 60 min. The results demonstrated that CoS with 3D nanoparticle morphology, prepared by microwave sulfurization of 30 min, possessed the largest specific surface area and electrochemically active surface area. These nanostructured features resulted in the promoted accessibility of active sites, enhanced mass/charge transport and easier release of hydrogen bubbles, rendering its highest HER activity and excellent stability and showing small overpotentials of 233, 314, and 364 mV to achieve current densities of 10, 50, and 100 mA cm−2, respectively, in neutral water.
