Enhancing Hydrogen Evolution Activity in Water Splitting by Tailoring Li+-Ni(OH)2-Pt Interfaces
02 Dec 2011-Science (American Association for the Advancement of Science)-Vol. 334, Iss: 6060, pp 1256-1260
TL;DR: It is found that a controlled arrangement of nanometer-scale Ni(OH)2 clusters on platinum electrode surfaces manifests a factor of 8 activity increase in catalyzing the hydrogen evolution reaction relative to state-of-the-art metal and metal-oxide catalysts.
Abstract: Improving the sluggish kinetics for the electrochemical reduction of water to molecular hydrogen in alkaline environments is one key to reducing the high overpotentials and associated energy losses in water-alkali and chlor-alkali electrolyzers. We found that a controlled arrangement of nanometer-scale Ni(OH)(2) clusters on platinum electrode surfaces manifests a factor of 8 activity increase in catalyzing the hydrogen evolution reaction relative to state-of-the-art metal and metal-oxide catalysts. In a bifunctional effect, the edges of the Ni(OH)(2) clusters promoted the dissociation of water and the production of hydrogen intermediates that then adsorbed on the nearby Pt surfaces and recombined into molecular hydrogen. The generation of these hydrogen intermediates could be further enhanced via Li(+)-induced destabilization of the HO-H bond, resulting in a factor of 10 total increase in activity.
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TL;DR: Measurements of activity as a function of film thickness on Au and glassy carbon substrates are consistent with the hypothesis that Fe exerts a partial-charge-transfer activation effect on Ni, similar to that observed for noble-metal electrode surfaces.
Abstract: Fe plays a critical, but not yet understood, role in enhancing the activity of the Ni-based oxygen evolution reaction (OER) electrocatalysts. We report electrochemical, in situ electrical, photoelectron spectroscopy, and X-ray diffraction measurements on Ni1–xFex(OH)2/Ni1–xFexOOH thin films to investigate the changes in electronic properties, OER activity, and structure as a result of Fe inclusion. We developed a simple method for purification of KOH electrolyte that uses precipitated bulk Ni(OH)2 to absorb Fe impurities. Cyclic voltammetry on rigorously Fe-free Ni(OH)2/NiOOH reveals new Ni redox features and no significant OER current until >400 mV overpotential, different from previous reports which were likely affected by Fe impurities. We show through controlled crystallization that β-NiOOH is less active for OER than the disordered γ-NiOOH starting material and that previous reports of increased activity for β-NiOOH are due to incorporation of Fe-impurities during the crystallization process. Through...
2,419 citations
TL;DR: The overall catalytic activities for these reaction as a function of a more fundamental property, a descriptor, OH-M(2+δ) bond strength (0 ≤ δ ≤ 1.5), provide the foundation for rational design of 'active sites' for practical alkaline HER and OER electrocatalysts.
Abstract: Design and synthesis of materials for efficient electrochemical transformation of water to molecular hydrogen and of hydroxyl ions to oxygen in alkaline environments is of paramount importance in reducing energy losses in water–alkali electrolysers. Here, using 3d-M hydr(oxy)oxides, with distinct stoichiometries and morphologies in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) regions, we establish the overall catalytic activities for these reaction as a function of a more fundamental property, a descriptor, OH–M2+δ bond strength (0 ≤ δ ≤ 1.5). This relationship exhibits trends in reactivity (Mn < Fe < Co < Ni), which is governed by the strength of the OH–M2+δ energetic (Ni < Co < Fe < Mn). These trends are found to be independent of the source of the OH, either the supporting electrolyte (for the OER) or the water dissociation product (for the HER). The successful identification of these electrocatalytic trends provides the foundation for rational design of ‘active sites’ for practical alkaline HER and OER electrocatalysts. Efficient electrochemical transformation of water to molecular hydrogen and of hydroxyl ions to oxygen in alkaline environments is important for reducing energy losses in water–alkali electrolysers. Insight into the activities of hydr(oxy)oxides on platinum catalyst surfaces for hydrogen and oxygen evolution reactions should prove significant for designing practical alkaline electrocatalysts.
2,271 citations
TL;DR: A highly active and durable class of electrocatalysts is synthesized by exploiting the structural evolution of platinum-nickel (Pt-Ni) bimetallic nanocrystals by exploitingThe starting material, crystalline PtNi3 polyhedra, transforms in solution by interior erosion into Pt3Ni nanoframes with surfaces that offer three-dimensional molecular accessibility.
Abstract: Control of structure at the atomic level can precisely and effectively tune catalytic properties of materials, enabling enhancement in both activity and durability. We synthesized a highly active and durable class of electrocatalysts by exploiting the structural evolution of platinum-nickel (Pt-Ni) bimetallic nanocrystals. The starting material, crystalline PtNi3 polyhedra, transforms in solution by interior erosion into Pt3Ni nanoframes with surfaces that offer three-dimensional molecular accessibility. The edges of the Pt-rich PtNi3 polyhedra are maintained in the final Pt3Ni nanoframes. Both the interior and exterior catalytic surfaces of this open-framework structure are composed of the nanosegregated Pt-skin structure, which exhibits enhanced oxygen reduction reaction (ORR) activity. The Pt3Ni nanoframe catalysts achieved a factor of 36 enhancement in mass activity and a factor of 22 enhancement in specific activity, respectively, for this reaction (relative to state-of-the-art platinum-carbon catalysts) during prolonged exposure to reaction conditions.
2,252 citations
TL;DR: Analyses indicate that the enhanced electrocatalytic activity of WS₂ is associated with the high concentration of the strained metallic 1T (octahedral) phase in the as-exfoliated nanosheets.
Abstract: Efficient evolution of hydrogen via electrocatalysis at low overpotentials is promising for clean energy production. Monolayered nanosheets of chemically exfoliated WS2 are shown to be efficient catalysts for hydrogen evolution at very low overpotentials. The enhanced catalytic performance is associated with the high concentration of the strained metallic octahedral phase in the exfoliated nanosheets.
2,249 citations
TL;DR: Detailed kinetic analyses of aqueous electrochemistry involving gaseous H2 or O2 involving hydrogen evolution reaction, hydrogen oxidation reaction, oxygen reduction reaction, and oxygen evolution reaction are revisited and the limitation of Butler-Volmer expression in electrocatalysis is discussed.
Abstract: Microkinetic analyses of aqueous electrochemistry involving gaseous H2 or O2, i.e., hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), are revisited. The Tafel slopes used to evaluate the rate determining steps generally assume extreme coverage of the adsorbed species (θ ≈ 0 or ≈1), although, in practice, the slopes are coverage-dependent. We conducted detailed kinetic analyses describing the coverage-dependent Tafel slopes for the aforementioned reactions. Our careful analyses provide a general benchmark for experimentally observed Tafel slopes that can be assigned to specific rate determining steps. The Tafel analysis is a powerful tool for discussing the rate determining steps involved in electrocatalysis, but our study also demonstrated that overly simplified assumptions led to an inaccurate description of the surface electrocatalysis. Additionally, in many studies, Tafel analyses have been performed in conjunction with the Butler-Volmer equation, where its applicability regarding only electron transfer kinetics is often overlooked. Based on the derived kinetic description of the HER/HOR as an example, the limitation of Butler-Volmer expression in electrocatalysis is also discussed in this report.
1,830 citations
References
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TL;DR: The active site for hydrogen evolution, a reaction catalyzed by precious metals, on nanoparticulate molybdenum disulfide (MoS2) is determined by atomically resolving the surface of this catalyst before measuring electrochemical activity in solution.
Abstract: The identification of the active sites in heterogeneous catalysis requires a combination of surface sensitive methods and reactivity studies. We determined the active site for hydrogen evolution, a reaction catalyzed by precious metals, on nanoparticulate molybdenum disulfide (MoS2) by atomically resolving the surface of this catalyst before measuring electrochemical activity in solution. By preparing MoS2 nanoparticles of different sizes, we systematically varied the distribution of surface sites on MoS2 nanoparticles on Au(111), which we quantified with scanning tunneling microscopy. Electrocatalytic activity measurements for hydrogen evolution correlate linearly with the number of edge sites on the MoS2 catalyst.
4,930 citations
TL;DR: A density functional theory-based, high-throughput screening scheme that successfully uses these strategies to identify a new electrocatalyst for the hydrogen evolution reaction (HER), which is found to have a predicted activity comparable to, or even better than, pure Pt, the archetypical HER catalyst.
Abstract: The pace of materials discovery for heterogeneous catalysts and electrocatalysts could, in principle, be accelerated by the development of efficient computational screening methods. This would require an integrated approach, where the catalytic activity and stability of new materials are evaluated and where predictions are benchmarked by careful synthesis and experimental tests. In this contribution, we present a density functional theory-based, high-throughput screening scheme that successfully uses these strategies to identify a new electrocatalyst for the hydrogen evolution reaction (HER). The activity of over 700 binary surface alloys is evaluated theoretically; the stability of each alloy in electrochemical environments is also estimated. BiPt is found to have a predicted activity comparable to, or even better than, pure Pt, the archetypical HER catalyst. This alloy is synthesized and tested experimentally and shows improved HER performance compared with pure Pt, in agreement with the computational screening results.
3,134 citations
Book•
01 Mar 2003
TL;DR: In this article, the authors present a survey of fuel cell technologies and applications, focusing on hydrogen storage, hydrogen generation, and other energy conversion related topics, as well as their applications.
Abstract: VOLUME 1: FUNDAMENTALS AND SURVEY OF SYSTEMS. Contributors to Volume 1. Foreword. Preface. Abbreviations and Acronyms. Part 1: Thermodynamics and kinetics of fuel cell reactions. Part 2: Mass transfer in fuel cells. Part 3: Heat transfer in fuel cells. Part 4: Fuel cell principles, systems and applications. Contents for Volumes 2, 3 and 4. Subject Index. VOLUME 2: ELECTROCATALYSIS. Contributors to Volume 2. Foreword. Preface. Abbreviations and Acronyms. Part 1: Introduction. Part 2: Theory of electrocatalysis. Part 3: Methods in electrocatalysis. Part 4: The hydrogen oxidation/evolution reaction. Part 5: The oxygen reduction/evolution reaction. Part 6: Oxidation of small organic molecules. Part 7: Other energy conversion related topics. Contents for Volumes 1, 3 and 4. Subject Index. VOLUME 3: FUEL CELL TECHNOLOGY AND APPLICATIONS: PART 1. Contributors to Volumes 3 and 4. Foreword. Preface. Abbreviations and Acronyms. Part 1: Sustainable energy supply. Part 2: Hydrogen storage and hydrogen generation. Development prospects for hydrogen storage. Chemical hydrogen storage devices. Reforming of methanol and fuel processor development. Fuel processing from hydrocarbons to hydrogen. Well-to-wheel efficiencies. Hydrogen safety, codes and standards. Part 3: Polymer electrolyte membrane fuel cell systems (PEMFC). Bipolar plate materials and flow field design. Membrane materials. Electro-catalysts. Membrane-electrode-assembly (MEA). State-of-the-art performance and durability. VOLUME 4: FUEL CELL TECHNOLOGY AND APPLICATIONS, PART 2. Contributors to Volume 3 and 4. Foreword. Preface. Abbreviations and Acronyms. Part 3: Polymer electrolyte membrane fuel cells and systems (PEMFC) (Continued from previous volume). System design and system-specific aspects. Air-supply components. Applications based on PEM-technology. Part 4: Alkaline fuel cells and systems (AFC). Part 5: Phosphoric acid fuel cells and systems (PAFC). Part 6: Direct methanol fuel cells and systems (DMFC). Part 7: Molten carbonate fuel cells and systems (MCFC). Part 8: Solid oxide fuel cells and systems (SOFC). Materials. Stack and system design. New concepts. Part 9: Primary and secondary metal/air cells. Part 10: Portable fuel cell systems. Part 11: Current fuel cell propulsion systems. PEM fuel cell systems for cars/buses. PEM fuel cell systems for submarines. AFC fuel cell systems. Part 12: Electric utility fuel cell systems. Part 13: Future prospects of fuel cell systems. Contents for Volumes 1 and 2. Subject Index.
2,917 citations
TL;DR: It is reported here that for the class of nanostructured gold– or platinum–cerium oxide catalysts, which are active for the water-gas shift reaction, metal nanoparticles do not participate in the reaction.
Abstract: Traditional analysis of reactions catalyzed by supported metals involves the structure of the metallic particles. However, we report here that for the class of nanostructured gold- or platinum-cerium oxide catalysts, which are active for the water-gas shift reaction, metal nanoparticles do not participate in the reaction. Nonmetallic gold or platinum species strongly associated with surface cerium-oxygen groups are responsible for the activity.
2,616 citations
Book•
01 Jan 1994
TL;DR: In this paper, the electronic structure of transition metal-oxide surfaces is described. But the electronic structures of non-transition metaloxide surfaces have not been discussed, and they are not considered in this paper.
Abstract: 1. Introduction 2. Geometric structure of metal-oxide surfaces 3. Surface lattice vibrations 4. Electronic structure of non-transition metal-oxide surfaces 5. Electronic structure of transition metal-oxide surfaces 6. Molecular adsorption on oxides 7. Interfaces of metal oxides with metals and other oxides References Index.
2,523 citations