Water electrolysers with closed and open electrochemical systems

Lagadec, Marie Francine; Grimaud, Alexis

doi:10.1038/s41563-020-0788-3

Cited by 418 publications

(323 citation statements)

References 67 publications

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“…To be considered commercially relevant, HER current densities need to be over 1 A cm −2 , which requires large operating voltages. [ 19,43–45 ] However, there is only a 480 mV overpotential window for anode (oxygen evolution reaction electrode) to operate without any interference from chlorine evolution. [ 6,43 ] At a large cell voltage, the two‐electron CER will take place and produce corrosive hypochlorite.…”

Section: Figurementioning

confidence: 99%

Stable and Highly Efficient Hydrogen Evolution from Seawater Enabled by an Unsaturated Nickel Surface Nitride

et al. 2021

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This is because chlorine evolution takes place at the counter electrode and highly corrosive hypochlorite by-products block the active sites of the noble metal catalysts. [6,13,18] Consequently, development of stable and active electrocatalysts for seawater splitting is of crucial importance for this process. Transition metal nitrides (TMNs) have excellent electrical conductivity and corrosion resistance and have demonstrated good stability for seawater splitting. [18-20] However, most of the bulk TMNs reported exhibit unsatisfactory HER activity due to a suboptimal hydrogen bonding energy. [21,22] Consequently, material optimization strategies, such as vacancy engineering, alloying, interface engineering, and heteroatom doping are usually needed to improve their activity. [23-28] For example, interfacing MoN with C 3 N 4 can greatly promote HER activity in alkaline media. [29] Tungsten and phosphorus doping in Co 3 N can manipulate the dehydrogenation kinetics and increase hydrogen production. [27] Despite significant investigation into TMNs, adequate activity and corrosion resistance are still required to be achieved simultaneously, and more advanced modification methods need to be developed. Manipulating the stoichiometry is one such way to optimize the properties of TMNs. Using this strategy, the N atom ratio in the metal matrix can be tuned to regulate the TMN electronic structure. [18,24,25,30] The two main approaches to controlling the nitrogen content in TMNs are the nitrogen-rich process and the incomplete nitridation process. [31-33] The nitrogen-rich process aims to embed extra nitrogen atoms into the TMN lattice but usually requires high-temperature and high-pressure conditions due to sluggish thermodynamics. [30,31,34,35] The incomplete nitridation process can limit the metal-nitrogen bonding in the matrix and promote the formation of metal/ metal nitride interfaces, which generally offers better conductivity and subsequent electrocatalytic activity. [23,25,33,36] However, the stoichiometry in a metal/metal nitride heterostructure is difficult to control and deficient or superfluous nitridation can lead to poor electrocatalytic activity. Herein, we synthesized a nickel surface nitride encapsulated in a carbon shell (Ni-SN@C) using an unsaturated nitriding process. Compared to conventional TMNs or metal/metal nitride heterostructures, the unsaturated Ni-SN@C has no detectable bulk nickel nitride phase. Instead, the main chemical composition of Ni-SN@C is metallic Ni but with unique Electrocatalytic production of hydrogen from seawater provides a route to low-cost and clean energy conversion. However, the hydrogen evolution reaction (HER) using seawater is greatly hindered by the lack of active and stable catalysts. Herein, an unsaturated nickel surface nitride (Ni-SN@C) catalyst that is active and stable for the HER in alkaline seawater is prepared. It achieves a low overpotential of 23 mV at a current density of 10 mA cm −2 in alkaline seawater electrolyte, which is superior to Pt/C. Compared to conv...

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Section: Figurementioning

confidence: 99%

Stable and Highly Efficient Hydrogen Evolution from Seawater Enabled by an Unsaturated Nickel Surface Nitride

et al. 2021

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“…For example, Cronin and co-workers used phosphomolybdic acid as the "electron buffer" to spatially decouple the OER and HER. Other (in)soluble redox mediators were also proposed, such as [Fe(CN) 6 ] 4− /[Fe(CN) 6 ] 3− , V 3+ /V 4+ and NiOOH/Ni(OH) 2 [28][29][30][31][32] . A further advantage of this approach is that it offers the opportunity of coupling water splitting with battery technologies for concurrent energy storage 33,34 .…”

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confidence: 99%

A membrane-free flow electrolyzer operating at high current density using earth-abundant catalysts for water splitting

et al. 2021

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Electrochemical water splitting is one of the most sustainable approaches for generating hydrogen. Because of the inherent constraints associated with the architecture and materials, the conventional alkaline water electrolyzer and the emerging proton exchange membrane electrolyzer are suffering from low efficiency and high materials/operation costs, respectively. Herein, we design a membrane-free flow electrolyzer, featuring a sandwich-like architecture and a cyclic operation mode, for decoupled overall water splitting. Comprised of two physically-separated compartments with flowing H2-rich catholyte and O2-rich anolyte, the cell delivers H2 with a purity >99.1%. Its low internal ohmic resistance, highly active yet affordable bifunctional catalysts and efficient mass transport enable the water splitting at current density of 750 mA cm−2 biased at 2.1 V. The eletrolyzer works equally well both in deionized water and in regular tap water. This work demonstrates the opportunity of combining the advantages of different electrolyzer concepts for water splitting via cell architecture and materials design, opening pathways for sustainable hydrogen generation.

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“…In spite of having such advantages, water electrosplitting lacks in energy‐efficiency and also suffers from a very low abundance of the best active catalysts which have been the main reasons for hindering its successful commercialization [22–24] . Affordability of hydrogen produced during catalytic water electrosplitting is determined primarily by the activity and the availability of electrode materials used [25, 26] . Materials that perform the half‐cell reactions (oxygen evolution reaction (OER) at the anode and hydrogen evolution reaction (HER) at the cathode) with a better energy efficiency (i.e., with lower overpotentials) involve Pt (for HER) and the oxides of Ir and Ru (for OER).…”

Section: Introductionmentioning

confidence: 99%

“…Materials that perform the half‐cell reactions (oxygen evolution reaction (OER) at the anode and hydrogen evolution reaction (HER) at the cathode) with a better energy efficiency (i.e., with lower overpotentials) involve Pt (for HER) and the oxides of Ir and Ru (for OER). These metals are very low in abundance that forbids the successful scale‐up of water electrolysers for large‐scale hydrogen production [25, 26] . To avoid this issue with these precious metals based electrocatalysts, several strategies were proposed and noteworthy ones are nanostructuring and noble metal dilution by alloying and soft‐templating in colloidal solutions [27–31] .…”

Section: Introductionmentioning

confidence: 99%

Strategies and Perspectives to Catch the Missing Pieces in Energy‐Efficient Hydrogen Evolution Reaction in Alkaline Media

et al. 2021

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Transition metal hydroxides (M‐OH) and their heterostructures (X|M‐OH, where X can be a metal, metal oxide, metal chalcogenide, metal phosphide, etc.) have recently emerged as highly active electrocatalysts for hydrogen evolution reaction (HER) of alkaline water electrolysis. Lattice hydroxide anions in metal hydroxides are primarily responsible for observing such an enhanced HER activity in alkali that facilitate water dissociation and assist the first step, the hydrogen adsorption. Unfortunately, their poor electronic conductivity had been an issue of concern that significantly lowered its activity. Interesting advancements were made when heterostructured hydroxide materials with a metallic and or a semiconducting phase were found to overcome this pitfall. However, in the midst of recently evolving metal chalcogenide and phosphide based HER catalysts, significant developments made in the field of metal hydroxides and their heterostructures catalysed alkaline HER and their superiority have unfortunately been given negligible attention. This review, unlike others, begins with the question of why alkaline HER is difficult and will take the reader through evaluation perspectives, trends in metals hydroxides and their heterostructures catalysed HER, an understanding of how alkaline HER works on different interfaces, what must be the research directions of this field in near future, and eventually summarizes why metal hydroxides and their heterostructures are inevitable for energy‐efficient alkaline HER.

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Water electrolysers with closed and open electrochemical systems

Cited by 418 publications

References 67 publications

Stable and Highly Efficient Hydrogen Evolution from Seawater Enabled by an Unsaturated Nickel Surface Nitride

Stable and Highly Efficient Hydrogen Evolution from Seawater Enabled by an Unsaturated Nickel Surface Nitride

A membrane-free flow electrolyzer operating at high current density using earth-abundant catalysts for water splitting

Strategies and Perspectives to Catch the Missing Pieces in Energy‐Efficient Hydrogen Evolution Reaction in Alkaline Media

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