Solar-driven, highly sustained splitting of seawater into hydrogen and oxygen fuels
02 Apr 2019-Proceedings of the National Academy of Sciences of the United States of America (National Academy of Sciences)-Vol. 116, Iss: 14, pp 6624-6629
TL;DR: A hierarchical anode consisting of a nickel–iron hydroxide electrocatalyst layer uniformly coated on a sulfide layer formed on Ni substrate was developed, affording superior catalytic activity and corrosion resistance in seawater electrolysis.
Abstract: Electrolysis of water to generate hydrogen fuel is an attractive renewable energy storage technology. However, grid-scale freshwater electrolysis would put a heavy strain on vital water resources. Developing cheap electrocatalysts and electrodes that can sustain seawater splitting without chloride corrosion could address the water scarcity issue. Here we present a multilayer anode consisting of a nickel–iron hydroxide (NiFe) electrocatalyst layer uniformly coated on a nickel sulfide (NiSx) layer formed on porous Ni foam (NiFe/NiSx-Ni), affording superior catalytic activity and corrosion resistance in solar-driven alkaline seawater electrolysis operating at industrially required current densities (0.4 to 1 A/cm2) over 1,000 h. A continuous, highly oxygen evolution reaction-active NiFe electrocatalyst layer drawing anodic currents toward water oxidation and an in situ-generated polyatomic sulfate and carbonate-rich passivating layers formed in the anode are responsible for chloride repelling and superior corrosion resistance of the salty-water-splitting anode.
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TL;DR: A three-dimensional core-shell metal-nitride catalyst consisting of NiFeN nanoparticles uniformly decorated on NiMoN nanorods supported on Ni foam serves as an eminently active and durable oxygen evolution reaction catalyst for alkaline seawater electrolysis.
Abstract: Seawater is one of the most abundant natural resources on our planet. Electrolysis of seawater is not only a promising approach to produce clean hydrogen energy, but also of great significance to seawater desalination. The implementation of seawater electrolysis requires robust and efficient electrocatalysts that can sustain seawater splitting without chloride corrosion, especially for the anode. Here we report a three-dimensional core-shell metal-nitride catalyst consisting of NiFeN nanoparticles uniformly decorated on NiMoN nanorods supported on Ni foam, which serves as an eminently active and durable oxygen evolution reaction catalyst for alkaline seawater electrolysis. Combined with an efficient hydrogen evolution reaction catalyst of NiMoN nanorods, we have achieved the industrially required current densities of 500 and 1000 mA cm−2 at record low voltages of 1.608 and 1.709 V, respectively, for overall alkaline seawater splitting at 60 °C. This discovery significantly advances the development of seawater electrolysis for large-scale hydrogen production. Seawater electrolysis is a promising approach to produce hydrogen fuel and is also of great significance to seawater desalination. Here, the authors prepare 3D core-shell metal-nitride catalysts from earth-abundant elements for high-performance alkaline seawater electrolysis.
572 citations
TL;DR: In this article, the historic development of water electrolysis is overviewed, and several critical electrochemical parameters are discussed, particularly focusing on catalyst synthesis, activity and stability challenges, performance improvement, and industry relevant developments.
Abstract: Hydrogen economy has emerged as a very promising alternative to the current hydrocarbon economy, which involves the process of harvesting renewable energy to split water into hydrogen and oxygen and then further utilization of clean hydrogen fuel. The production of hydrogen by water electrolysis is an essential prerequisite of the hydrogen economy with zero carbon emission. Among various water electrolysis technologies, alkaline water splitting has been commercialized for more than 100 years, representing the most mature and economic technology. Here, the historic development of water electrolysis is overviewed, and several critical electrochemical parameters are discussed. After that, advanced nonprecious metal electrocatalysts that emerged recently for negotiating the alkaline oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are discussed, including transition metal oxides, (oxy)hydroxides, chalcogenides, phosphides, and nitrides for the OER, as well as transition metal alloys, chalcogenides, phosphides, and carbides for the HER. In this section, particular attention is paid to the catalyst synthesis, activity and stability challenges, performance improvement, and industry-relevant developments. Some recent works about scaled-up catalyst synthesis, novel electrode designs, and alkaline seawater electrolysis are also spotlighted. Finally, an outlook on future challenges and opportunities for alkaline water splitting is offered, and potential future directions are speculated.
455 citations
TL;DR: In this article, the surface of Ni foam is engineered into a rough S-doped Ni/Fe (oxy)hydroxide layer, which exhibits extraordinary oxygen evolution reaction (OER) performance in both alkaline salty water and seawater electrolytes.
Abstract: Developing energy- and time-saving methods to synthesize active and stable oxygen evolving catalysts is of great significance to hydrogen production from water electrolysis, which however remains a grand challenge. Here we report a one-step approach to grow highly porous S-doped Ni/Fe (oxy)hydroxide catalysts on Ni foam in several minutes under room temperature. This ultrafast method effectively engineers the surface of Ni foam into a rough S-doped Ni/Fe (oxy)hydroxide layer, which has multiple levels of porosity and good hydrophilic features and exhibits extraordinary oxygen evolution reaction (OER) performance in both alkaline salty water and seawater electrolytes. Specifically, the S-doped Ni/Fe (oxy)hydroxide catalyst requires low overpotentials of 300 and 398 mV to deliver current densities of 100 and 500 mA cm−2, respectively, when directly used as an OER catalyst in alkaline natural seawater electrolyte. Using this OER catalyst together with an efficient hydrogen evolution reaction catalyst, we have achieved the commercially demanded current densities of 500 and 1000 mA cm−2 at low voltages of 1.837 and 1.951 V, respectively, for overall alkaline seawater electrolysis at room temperature with very good durability. This work affords a cost-efficient surface engineering method to steer commercial Ni foam into robust OER catalysts for seawater electrolysis, which has important implications for both the hydrogen economy and environmental remediation.
367 citations
TL;DR: The electrocatalytic oxygen evolution reaction (OER) is a core reaction responsible for converting renewable electricity into storable fuels; yet, it is kinetically challenging, because of the complex complex OER as discussed by the authors.
Abstract: Electrocatalytic oxygen evolution reaction (OER) is a core reaction responsible for converting renewable electricity into storable fuels; yet, it is kinetically challenging, because of the complex ...
315 citations
References
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TL;DR: The battery systems reviewed here include sodium-sulfur batteries that are commercially available for grid applications, redox-flow batteries that offer low cost, and lithium-ion batteries whose development for commercial electronics and electric vehicles is being applied to grid storage.
Abstract: The increasing interest in energy storage for the grid can be attributed to multiple factors, including the capital costs of managing peak demands, the investments needed for grid reliability, and the integration of renewable energy sources. Although existing energy storage is dominated by pumped hydroelectric, there is the recognition that battery systems can offer a number of high-value opportunities, provided that lower costs can be obtained. The battery systems reviewed here include sodium-sulfur batteries that are commercially available for grid applications, redox-flow batteries that offer low cost, and lithium-ion batteries whose development for commercial electronics and electric vehicles is being applied to grid storage.
11,144 citations
"Solar-driven, highly sustained spli..." refers background in this paper
...S renewable energy by driving uphill chemical reactions is an attractive solution to the intermittency problem faced by many alternative energy sources (1, 2)....
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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
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TL;DR: Solar energy is by far the largest exploitable resource, providing more energy in 1 hour to the earth than all of the energy consumed by humans in an entire year, and if solar energy is to be a major primary energy source, it must be stored and dispatched on demand to the end user.
Abstract: Global energy consumption is projected to increase, even in the face of substantial declines in energy intensity, at least 2-fold by midcentury relative to the present because of population and economic growth. This demand could be met, in principle, from fossil energy resources, particularly coal. However, the cumulative nature of CO2 emissions in the atmosphere demands that holding atmospheric CO2 levels to even twice their preanthropogenic values by midcentury will require invention, development, and deployment of schemes for carbon-neutral energy production on a scale commensurate with, or larger than, the entire present-day energy supply from all sources combined. Among renewable energy resources, solar energy is by far the largest exploitable resource, providing more energy in 1 hour to the earth than all of the energy consumed by humans in an entire year. In view of the intermittency of insolation, if solar energy is to be a major primary energy source, it must be stored and dispatched on demand to the end user. An especially attractive approach is to store solar-converted energy in the form of chemical bonds, i.e., in a photosynthetic process at a year-round average efficiency significantly higher than current plants or algae, to reduce land-area requirements. Scientific challenges involved with this process include schemes to capture and convert solar energy and then store the energy in the form of chemical bonds, producing oxygen from water and a reduced fuel such as hydrogen, methane, methanol, or other hydrocarbon species.
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TL;DR: Identifying and building a sustainable energy system are perhaps two of the most critical issues that today's society must address.
Abstract: Identifying and building a sustainable energy system are perhaps two of the most critical issues that today's society must address. Replacing our current energy carrier mix with a sustainable fuel is one of the key pieces in that system. Hydrogen as an energy carrier, primarily derived from water, can address issues of sustainability, environmental emissions, and energy security. Issues relating to hydrogen production pathways are addressed here. Future energy systems require money and energy to build. Given that the United States has a finite supply of both, hard decisions must be made about the path forward, and this path must be followed with a sustained and focused effort.
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TL;DR: In this paper, the authors report a protocol for evaluating the activity, stability, and Faradaic efficiency of electrodeposited oxygen-evolving electrocatalysts for water oxidation.
Abstract: Objective evaluation of the activity of electrocatalysts for water oxidation is of fundamental importance for the development of promising energy conversion technologies including integrated solar water-splitting devices, water electrolyzers, and Li-air batteries. However, current methods employed to evaluate oxygen-evolving catalysts are not standardized, making it difficult to compare the activity and stability of these materials. We report a protocol for evaluating the activity, stability, and Faradaic efficiency of electrodeposited oxygen-evolving electrocatalysts. In particular, we focus on methods for determining electrochemically active surface area and measuring electrocatalytic activity and stability under conditions relevant to an integrated solar water-splitting device. Our primary figure of merit is the overpotential required to achieve a current density of 10 mA cm–2 per geometric area, approximately the current density expected for a 10% efficient solar-to-fuels conversion device. Utilizing ...
4,808 citations