Large-scale industrial application of electrolytic splitting of water has called for the development of oxygen evolution electrodes that are inexpensive, robust and can deliver large current density (>500 mA cm−2) at low applied potentials. Here we show that an efficient oxygen electrode can be developed by electrodepositing amorphous mesoporous nickel–iron composite nanosheets directly onto macroporous nickel foam substrates. The as-prepared oxygen electrode exhibits high catalytic activity towards water oxidation in alkaline solutions, which only requires an overpotential of 200 mV to initiate the reaction, and is capable of delivering current densities of 500 and 1,000 mA cm−2 at overpotentials of 240 and 270 mV, respectively. The electrode also shows prolonged stability against bulk water electrolysis at large current. Collectively, the as-prepared three-dimensional structured electrode is the most efficient oxygen evolution electrode in alkaline electrolytes reported to the best of our knowledge, and can potentially be applied for industrial scale water electrolysis.

Large-scale storage of renewable energy in the form of hydrogen (H2) fuel via electrolytic water splitting requires the development of water oxidation catalysts that are efficient and abundant. Carbon-based nanomaterials such as carbon nanotubes have attracted significant applications for use as substrates for anchoring metal-based nanoparticles. We show that, upon mild surface oxidation, hydrothermal annealing and electrochemical activation, multiwall carbon nanotubes (MWCNTs) themselves are effective water oxidation catalysts, which can initiate the oxygen evolution reaction (OER) at overpotentials of 0.3 V in alkaline media. Oxygen-containing functional groups such as ketonic C═O generated on the outer wall of MWCNTs are found to play crucial roles in catalyzing OER by altering the electronic structures of the adjacent carbon atoms and facilitates the adsorption of OER intermediates. The well-preserved microscopic structures and highly conductive inner walls of MWCNTs enable efficient transport of the electrons generated during OER.

3515wileyonlinelibrary.com OER and HER catalysts based on the earth-abundant fi rst row transition metals (Fe, Co, and Ni, etc.) has received extensive research interest. [9][10][11][12][13] Although signifi cant progress has been achieved, great challenges remain for nonprecious catalysts to achieve activity and stability that are comparable to conventional precious metals. To this end, one promising approach is to develop multimetallic/carbon catalysts by taking advantage of abundant metal-metal and metal-carbon synergistic interactions to enhance the performance of nonprecious catalysts. [14][15][16] The NiFe (oxy)hydroxide-based catalysts are regarded as one of the best performing nonprecious OER electrocatalysts in alkaline solutions, [17][18][19][20][21] which can be synthesized by coupling with carbon nanotube or graphene to achieve better conductivity and synergistic effects via hydrothermal, [ 19,22 ] or electrodeposition onto gold, glassy carbon, and nickel foam, etc., conductive current collector substrates. [ 19,23,24 ] The high OER activities of NiFe catalysts are generally attributed to a strong synergistic effect upon the incorporation of Fe, even in trace amount, into NiOOH, although the complete mechanisms and structural characteristics are not yet fully understood. [ 19,23 ] NiFe catalysts also have been reported for HER in alkaline media, [ 25 ] although the synergistic effect for HER is not as signifi cant as that for OER, and the reported activity for HER is relatively low compared to state-of-the-art nonprecious HER catalysts. Nevertheless, using the same catalyst as both the anode and cathode in an electrolysis device is very attractive, which could not only signifi cantly improve the integration and simplifi cation of the water splitting system, but also provide the feasibility of industrial application of water splitting technology.Besides having an effi cient catalyst, rational design of catalyst structure is known to be crucial for improving the electrode performance. In pursuit of creating large surface area and high active site density, various attempts have been devoted to developing 3D nanostructured catalyst materials, [26][27][28] such as mesoporous NiFe nanosheets, [ 24 ] NiCo 2 O 4 nanosheets/halloysite nanotubes, [ 26 ] hierarchically structured carbon microfi bre, [ 29 ] and multilayered TiO 2 nanowire arrays. [ 30 ] Moreover, smart design of a catalyst with macroscopic structure onto conductive porous support (e.g., nickel foam) could afford Bifunctional Porous NiFe/NiCo 2 O 4 /Ni Foam Electrodes with Triple Hierarchy and Double Synergies for Effi cient Whole Cell Water SplittingChanglong Xiao , Yibing Li , Xunyu Lu , and Chuan Zhao * A 3D hierarchical porous catalyst architecture based on earth abundant metals Ni, Fe, and Co has been fabricated through a facile hydrothermal and electrodeposition method for effi cient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The electrode is comprised of three levels of porous structures including the bottom su...

The electrocatalytic nitrogen reduction reaction (NRR) is a promising catalytic system for N 2 fixation in ambient conditions. Currently, metal-based catalysts are the most widely studied catalysts for electrocatalytic NRR. Unfortunately, the low selectivity and poor resistance to acids and bases, the low Faradaic efficiency, production rate, and stability of metal-based catalysts for NRR make them uncompetitive for the synthesis of ammonia in comparison to the industrial Haber-Bosch process. Inspired by applications of carbon-based metal-free catalysts (CMFCs) for oxygen reduction reaction (ORR) and CO 2 reduction reaction (CO 2 RR), the studies of these CMFCs in electrocatalytic NRR have attracted great attention in the past year. However, due to the differences in electrocatalytic NRR, there are several critical issues that need to be addressed in order to achieve rational design of advanced carbon-based metal-free electrocatalysts to improve activity, selectivity, and stability for NRR. This research news presents the recent developments in the field of carbon-based metal-free NRR catalysts,

Critical to the feasibility of electrochemical reduction of waste NOx (NOxRR), as a sustainable pathway and to close the NOx cycle for the emerging NH3 economy, is the requirement of...

The facile and scalable synthesis of manganese-doped nickel/nickel oxide heterostructures with high activity, outperforming the Pt benchmark, in neutral electrolytes.

Crystalline cobalt oxide nanoparticles have been densely and strongly anchored onto mildly oxidized multiwalled carbon nanotubes (Co 3 O 4 /mMWCNT) and applied as electrocatalysts for highly efficient water oxidation. The hybrid catalyses oxygen evolution reactions (OER) with an onset potential of 1.51 V vs. RHE and an overpotential only of 390 mV to achieve a current density of 10 mA cm À2 . The Co 3 O 4 /mMWCNT catalyst exhibits high Faraday efficiency (>99%) and long-term stability (>25 h) during bulk electrolysis of water. A range of carbon nanostructures including MWCNTs, single-walled CNTs (SWCNTs), and graphene, and CNTs of different oxidation states have been prepared and applied as substrates for Co 3 O 4 nanocrystals and their performance is compared to reveal the interrelationship between the nanocarbon structure, surface functionalization and charge transport for rational design of OER catalysts. Furthermore, a range of techniques has been utilized to characterize the stability of MWCNT substrates during water oxidation. Importantly, it is found that the MWCNTs in the composite can sustain the harsh oxidative environment of water oxidation, with no carbon corrosion detected.

An electrochemical method based on cathodic stripping voltammetry at a gold electrode has been developed for the determination of water in ionic liquids. The technique has been applied to two aprotic ionic liquids, (1-butyl-3-ethylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate), and two protic ionic liquids, (bis(2-hydroxyethyl)ammonium acetate and triethylammonium acetate). When water is present in an ionic liquid, electrooxidation of a gold electrode forms gold oxides. Thus, application of an anodic potential scan or holding the potential of the electrode at a very positive value leads to accumulation of an oxide film. On applying a cathodic potential scan, a sensitive stripping peak is produced as a result of the reduction of gold oxide back to gold. The magnitude of the peak current generated from the stripping process is a function of the water concentration in an ionic liquid. The method requires no addition of reagents and can be used for the sensitive and in situ determination of water present in small volumes of ionic liquids. Importantly, the method allows the determination of water in the carboxylic acid-based ionic liquids, such as acetate-based protic ionic liquids, where the widely used Karl Fischer titration method suffering from an esterification side reaction which generates water as a side product.