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Journal ArticleDOI

CuCo Hybrid Oxides as Bifunctional Electrocatalyst for Efficient Water Splitting

Min Kuang1, Peng Han1, Qihao Wang1, Jun Li1, Gengfeng Zheng1 
01 Dec 2016-Advanced Functional Materials (John Wiley & Sons, Ltd)-Vol. 26, Iss: 46, pp 8555-8561
TL;DR: In this paper, a type of 1D copper-cobalt hybrid oxide nanowires (CuCoO-NWs) is developed via a facile two-step growth-conversion process toward a bifunctional water splitting catalyst.
Abstract: Solar-driven water splitting is a promising approach for renewable energy, where the development of efficient and stable bifunctional electrocatalysts for simultaneously producing hydrogen and oxygen is still challenging Herein, combined with the hydrogen evolution reaction (HER) activity of a copper(I) complex and oxygen evolution reaction (OER) activity of cobalt-based oxides, a type of 1D copper-cobalt hybrid oxide nanowires (CuCoO-NWs) is developed via a facile two-step growth-conversion process toward a bifunctional water splitting catalyst The CuCoO-NWs exhibit excellent catalytic performances for both HER and OER in the same basic electrolyte, with optimized low onset overpotentials and high current densities The efficient HER activity is ascribed to the formation of Cu2O, while the activity for OER is primarily enabled by Co-based oxides and abundant oxygen vacancies The CuCoO-NWs allow for the assembly of a water electrolyzer with strong alkaline media, with a current density of 10 mA cm−2 at 161 V Further combination with a commercial silicon photovoltaic allows the direct use of solar energy for spontaneous water splitting with excellent stability for over 72 h, suggesting the potential as a promising bifunctional electrocatalyst for efficient solar-driven water splitting
Citations
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Journal ArticleDOI
TL;DR: The fundamentals of HER are summarized and the recent state-of-the-art advances in the low-cost and high-performance catalysts based on noble and non-noble metals, as well as metal-free HER electrocatalysts are reviewed.
Abstract: Hydrogen fuel is considered as the cleanest renewable resource and the primary alternative to fossil fuels for future energy supply. Sustainable hydrogen generation is the major prerequisite to realize future hydrogen economy. The electrocatalytic hydrogen evolution reaction (HER), as the vital step of water electrolysis to H2 production, has been the subject of extensive study over the past decades. In this comprehensive review, we first summarize the fundamentals of HER and review the recent state-of-the-art advances in the low-cost and high-performance catalysts based on noble and non-noble metals, as well as metal-free HER electrocatalysts. We systemically discuss the insights into the relationship among the catalytic activity, morphology, structure, composition, and synthetic method. Strategies for developing an effective catalyst, including increasing the intrinsic activity of active sites and/or increasing the number of active sites, are summarized and highlighted. Finally, the challenges, perspectives, and research directions of HER electrocatalysis are featured.

1,387 citations

Journal ArticleDOI
TL;DR: The recent development of this concept is reviewed here and a novel principle for the design of oxygen electrocatalysts is proposed and an overview of the defects in carbon-based, metal-free electrocatalysis for ORR and various defects in metal oxides/selenides for OER is provided.
Abstract: Oxygen electrocatalysis, including the oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER), is a critical process for metal-air batteries Therefore, the development of electrocatalysts for the OER and the ORR is of essential importance Indeed, various advanced electrocatalysts have been designed for the ORR or the OER; however, the origin of the advanced activity of oxygen electrocatalysts is still somewhat controversial The enhanced activity is usually attributed to the high surface areas, the unique facet structures, the enhanced conductivities, or even to unclear synergistic effects, but the importance of the defects, especially the intrinsic defects, is often neglected More recently, the important role of defects in oxygen electrocatalysis has been demonstrated by several groups To make the defect effect clearer, the recent development of this concept is reviewed here and a novel principle for the design of oxygen electrocatalysts is proposed An overview of the defects in carbon-based, metal-free electrocatalysts for ORR and various defects in metal oxides/selenides for OER is also provided The types of defects and controllable strategies to generate defects in electrocatalysts are presented, along with techniques to identify the defects The defect-activity relationship is also explored by theoretical methods

1,222 citations

Journal ArticleDOI
TL;DR: Transition metal phosphides (TMPs) have attracted growing interest as heterogeneous electrocatalysts for overall water splitting as discussed by the authors, and several strategies have been developed for preparing TMPs with enhanced HER or OER performance.

494 citations

Journal ArticleDOI
TL;DR: In this article, a Cu, Co-embedded nitrogen-enriched mesoporous carbon framework (CuCo@NC) is developed using, a facile Cu-confined thermal conversion strategy of zeolitic imidazolate frameworks (ZIF-67) pre-grown on Cu(OH)2 nanowires.
Abstract: Rational synthesis of hybrid, earth-abundant materials with efficient electrocatalytic functionalities are critical for sustainable energy applications. Copper is theoretically proposed to exhibit high reduction capability close to Pt, but its high diffusion behavior at elevated fabrication temperatures limits its homogeneous incorporation with carbon. Here, a Cu, Co-embedded nitrogen-enriched mesoporous carbon framework (CuCo@NC) is developed using, a facile Cu-confined thermal conversion strategy of zeolitic imidazolate frameworks (ZIF-67) pre-grown on Cu(OH)2 nanowires. Cu ions formed below 450 °C are homogeneously confined within the pores of ZIF-67 to avoid self-aggregation, while the existence of CuN bonds further increases the nitrogen content in carbon frameworks derived from ZIF-67 at higher pyrolysis temperatures. This CuCo@NC electrocatalyst provides abundant active sites, high nitrogen doping, strong synergetic coupling, and improved mass transfer, thus significantly boosting electrocatalytic performances in oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). A high half-wave potential (0.884 V vs reversible hydrogen potential, RHE) and a large diffusion-limited current density are achieved for ORR, comparable to or exceeding the best reported earth-abundant ORR electrocatalysts. In addition, a low overpotential (145 mV vs RHE) at 10 mA cm−2 is demonstrated for HER, further suggesting its great potential as an efficient electrocatalyst for sustainable energy applications.

438 citations

Journal ArticleDOI
TL;DR: A novel "adsorption-calcination-reduction" strategy to synthesize spinel transitional metal oxides with a unique necklace-like multishelled hollow structure exploiting sacrificial templates of carbonaceous microspheres, which could prove to be an effective general strategy for the preparation of complex, hollow structures and functionalities.
Abstract: The durability and reactivity of catalysts can be effectively and precisely controlled through the careful design and engineering of their surface structures and morphologies. Herein, we develop a novel “adsorption–calcination–reduction” strategy to synthesize spinel transitional metal oxides with a unique necklace-like multishelled hollow structure exploiting sacrificial templates of carbonaceous microspheres, including NiCo2O4 (NCO), CoMn2O4, and NiMn2O4. Importantly, benefiting from the unique structures and reduction treatment to offer rich oxygen vacancies, the unique reduced NCO (R-NCO) as a bifunctional electrocatalyst exhibits the dual characteristics of good stability as well as high electrocatalytic activity for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). At 1.61 V cell voltage, a 10 mA cm–2 water splitting current density is obtained from the dual-electrode, alkaline water electrolyzer. Calculations based on density functional theory (DFT) reveal a mechanism ...

396 citations

References
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Journal ArticleDOI
TL;DR: The biggest challenge is whether or not the goals need to be met to fully utilize solar energy for the global energy demand can be met in a costeffective way on the terawatt scale.
Abstract: Energy harvested directly from sunlight offers a desirable approach toward fulfilling, with minimal environmental impact, the need for clean energy. Solar energy is a decentralized and inexhaustible natural resource, with the magnitude of the available solar power striking the earth’s surface at any one instant equal to 130 million 500 MW power plants.1 However, several important goals need to be met to fully utilize solar energy for the global energy demand. First, the means for solar energy conversion, storage, and distribution should be environmentally benign, i.e. protecting ecosystems instead of steadily weakening them. The next important goal is to provide a stable, constant energy flux. Due to the daily and seasonal variability in renewable energy sources such as sunlight, energy harvested from the sun needs to be efficiently converted into chemical fuel that can be stored, transported, and used upon demand. The biggest challenge is whether or not these goals can be met in a costeffective way on the terawatt scale.2

8,037 citations

Journal ArticleDOI
TL;DR: The emphasis of this review is on the origin of the electrocatalytic activity of nanostructured catalysts toward a series of key clean energy conversion reactions by correlating the apparent electrode performance with their intrinsic electrochemical properties.
Abstract: A fundamental change has been achieved in understanding surface electrochemistry due to the profound knowledge of the nature of electrocatalytic processes accumulated over the past several decades and to the recent technological advances in spectroscopy and high resolution imaging. Nowadays one can preferably design electrocatalysts based on the deep theoretical knowledge of electronic structures, via computer-guided engineering of the surface and (electro)chemical properties of materials, followed by the synthesis of practical materials with high performance for specific reactions. This review provides insights into both theoretical and experimental electrochemistry toward a better understanding of a series of key clean energy conversion reactions including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The emphasis of this review is on the origin of the electrocatalytic activity of nanostructured catalysts toward the aforementioned reactions by correlating the apparent electrode performance with their intrinsic electrochemical properties. Also, a rational design of electrocatalysts is proposed starting from the most fundamental aspects of the electronic structure engineering to a more practical level of nanotechnological fabrication.

3,918 citations

Journal ArticleDOI
26 Sep 2014-Science
TL;DR: It is shown that a pair of perovskite cells connected in series can power the electrochemical breakdown of water into hydrogen and oxygen efficiently, and the combination of the two yields a water-splitting photocurrent density and a solar-to-hydrogen efficiency of 12.3%.
Abstract: Although sunlight-driven water splitting is a promising route to sustainable hydrogen fuel production, widespread implementation is hampered by the expense of the necessary photovoltaic and photoelectrochemical apparatus. Here, we describe a highly efficient and low-cost water-splitting cell combining a state-of-the-art solution-processed perovskite tandem solar cell and a bifunctional Earth-abundant catalyst. The catalyst electrode, a NiFe layered double hydroxide, exhibits high activity toward both the oxygen and hydrogen evolution reactions in alkaline electrolyte. The combination of the two yields a water-splitting photocurrent density of around 10 milliamperes per square centimeter, corresponding to a solar-to-hydrogen efficiency of 12.3%. Currently, the perovskite instability limits the cell lifetime.

2,140 citations

Journal ArticleDOI
TL;DR: Current progress in this field is summarized here, especially highlighting several important bifunctional catalysts, and various approaches to improve or optimize the electrocatalysts are introduced.
Abstract: Water electrolysis is considered as the most promising technology for hydrogen production. Much research has been devoted to developing efficient electrocatalysts for hydrogen production via the hydrogen evolution reaction (HER) and oxygen production via the oxygen evolution reaction (OER). The optimum electrocatalysts can drive down the energy costs needed for water splitting via lowering the overpotential. A number of cobalt (Co)-based materials have been developed over past years as non-noble-metal heterogeneous electrocatalysts for HER and OER. Recent progress in this field is summarized here, especially highlighting several important bifunctional catalysts. Various approaches to improve or optimize the electrocatalysts are introduced. Finally, the current existing challenges and the future working directions for enhancing the performance of Co-implicated electrocatalysts are proposed.

1,963 citations

Journal ArticleDOI
TL;DR: An efficient Co3 O4 -based OER electrocatalyst is designed by a plasma-engraving strategy, which not only produced higher surface area, but also generated oxygen vacancies on Co 3 O4 surface with more Co(2+) formed to improve the electronic conductivity and create more active defects for OER.
Abstract: Co3O4, which is of mixed valences Co2+ and Co3+, has been extensively investigated as an efficient electrocatalyst for the oxygen evolution reaction (OER). The proper control of Co2+/Co3+ ratio in Co3O4 could lead to modifications on its electronic and thus catalytic properties. Herein, we designed an efficient Co3O4-based OER electrocatalyst by a plasma-engraving strategy, which not only produced higher surface area, but also generated oxygen vacancies on Co3O4 surface with more Co2+ formed. The increased surface area ensures the Co3O4 has more sites for OER, and generated oxygen vacancies on Co3O4 surface improve the electronic conductivity and create more active defects for OER. Compared to pristine Co3O4, the engraved Co3O4 exhibits a much higher current density and a lower onset potential. The specific activity of the plasma-engraved Co3O4 nanosheets (0.055 mA cm−2BET at 1.6 V) is 10 times higher than that of pristine Co3O4, which is contributed by the surface oxygen vacancies.

1,641 citations