Enhanced Oxygen Evolution Reaction Electrocatalysis via Electrodeposited Amorphous α-Phase Nickel-Cobalt Hydroxide Nanodendrite Forests

A self-supported porous NiMo electrocatalyst to boost the catalytic activity in the hydrogen evolution reaction

To develop hydrogen energy production and address the issues of global warming, inexpensive, effective, and long-lasting transition metal-based electrocatalysts for the synthesis of hydrogen are crucial. Herein, a porous electrocatalyst NiMo/Ni/NF was successfully constructed by a two-step electrodeposition process, and was used in the hydrogen evolution reaction (HER) of electrocatalytic water decomposition. NiMo nanoparticles were coated on porous Ni/NF grown on nickel foam (NF), leading to a resilient porous structure with enhanced conductivity for efficient charge transfer, as well as distinctive three-dimensional channels for quick electrolyte diffusion and gas release. Notably, the low overpotential (42 mV) and fast kinetics (Tafel slope of 44 mV dec-1) at a current density of 10 mA cm-2 in 1.0 M KOH solution demonstrate the excellent HER activity of the electrode, which was superior to that of recently reported non-noble metal-based catalysts. Additionally, NiMo/Ni/NF showed extraordinary catalytic durability in stability tests at a current density of 10 mA cm-2 for 70 h. The porous structure catalyst and the electrodeposition-electrocatalysis technique examined in this study offer new approaches for the advancement of the electrocatalysis field because of these benefits.

In Situ Reconstructed Mo-doped Amorphous FeOOH Boosts the Oxygen Evolution Reaction

Developing a fast and highly active oxygen evolution reaction (OER) catalyst to change energy kinetics technology is essential for making clean energy. Herein, we prepare three-dimensional (3D) hollow Mo-doped amorphous FeOOH (Mo-FeOOH) based on the precatalyst MoS₂ /FeC₂ O₄ via in situ reconstruction strategy. Mo-FeOOH exhibits promising OER performance. Specifically, it has an overpotential of 285 mV and a durability of 15 h at 10 mA cm^-2 . Characterizations indicate that Mo was included inside the FeOOH lattice, and it not only modifies the electronic energy levels of FeOOH but also effectively raises the inherent activity of FeOOH for OER. Additionally, in situ Raman analysis indicates that FeC₂ O₄ gradually transforms into the FeOOH active site throughout the OER process. This study provides ideas for designing in situ reconstruction strategies to prepare heteroatom doping catalysts for high electrochemical activity.

Cobalt-Doped Iron Phosphate Crystal on Stainless Steel Mesh for Corrosion-Resistant Oxygen Evolution Catalyst

We report an oxygen evolution reaction (OER) catalyst prepared by the incorporation of cobalt-doped iron phosphate on stainless steel mesh (SSM) through a one-step hydrothermal method. Compared to the catalytic property of bare SSM, our OER catalyst (0.84-CoFePi) showed a 42% improvement in current density at the potential of 1.9 V vs. RHE, and the onset potential was decreased by 26.5 mV. Furthermore, the loss in current density of bulk electrolysis after 12 h in 1 M KOH (pH 14) solution and 0.0441 wt% H2SO4 (pH ≈ 3) containing 0.1 M NaCl solution was negligible (3.1% and 3.2%, respectively). Moreover, our cobalt-doped iron phosphate on SSM exhibits the dramatic improvement in corrosion resistance to a basic, mild acidic solution and chloride ions compared to bare SSM.

High Selectivity Electrocatalysts for Oxygen Evolution Reaction and Anti-Chlorine Corrosion Strategies in Seawater Splitting

Seawater is one of the most abundant and clean hydrogen atom resources on our planet, so hydrogen production from seawater splitting has notable advantages. Direct electrolysis of seawater would not be in competition with growing demands for pure water. Using green electricity generated from renewable sources (e.g., solar, tidal, and wind energies), the direct electrolytic splitting of seawater into hydrogen and oxygen is a potentially attractive technology under the framework of carbon-neutral energy production. High selectivity and efficiency, as well as stable electrocatalysts, are prerequisites to facilitate the practical applications of seawater splitting. Even though the oxygen evolution reaction (OER) is thermodynamically favorable, the most desirable reaction process, the four-electron reaction, exhibits a high energy barrier. Furthermore, due to the presence of a high concentration of chloride ions (Cl−) in seawater, chlorine evolution reactions involving two electrons are more competitive. Therefore, intensive research efforts have been devoted to optimizing the design and construction of highly efficient and anticorrosive OER electrocatalysts. Based on this, in this review, we summarize the progress of recent research in advanced electrocatalysts for seawater splitting, with an emphasis on their remarkable OER selectivity and distinguished anti-chlorine corrosion performance, including the recent progress in seawater OER electrocatalysts with their corresponding optimized strategies. The future perspectives for the development of seawater-splitting electrocatalysts are also demonstrated.

Dumbbell-Shaped Ternary Transition-Metal (Cu, Ni, Co) Phosphate Bundles: A Promising Catalyst for the Oxygen Evolution Reaction

Development of economical and high-performance electrocatalysts for the oxygen evolution reaction (OER) is of tremendous interest for future applications as sustainable energy materials. Here, a unique member of efficient OER electrocatalysts has been developed based upon structurally versatile dumbbell-shaped ternary transition-metal (Cu, Ni, Co) phosphates with a three-dimensional (3D) (Cu₂(OH)(PO₄)/Ni₃(PO₄)₂·8H₂O/Co₃(PO₄)₂·8H₂O) (CNCP) structure. This structure is prepared using a simple aqueous stepwise addition of metal ion source approach. Various structural investigations demonstrate highly crystalline nature of the composite structure. Apart from the unique structural aspect, it is important that the CNCP composite structure has proved to be an excellent electrocatalyst for OER performance in comparison with its binary or constituent phosphate under alkaline and neutral conditions. Notably, the CNCP electrocatalyst displays a much lower overpotential of 224 mV at a current density of 10 mA cm^-2 and a lower Tafel slope of 53 mV dec^-1 with high stability in alkaline medium. In addition, X-ray photoelectron spectroscopy analysis suggested that the activity and long-term durability for the OER of the ternary 3D metal phosphate are due to the presence of electrochemically dynamic constituents such as Ni and Co and their resulting synergistic effects, which was further supported by theoretical studies. Theoretical calculations also reveal that the incredible OER execution was ascribed to the electron redistribution set off in the presence of Ni and Cu and the most favorable interaction between the *OOH intermediate and the active sites of CNCP. This work may attract the attention of researchers to construct efficient 3D ternary metal phosphate catalysts for various applications in the field of electrochemistry.

Electrochemically Deposited Amorphous Cobalt-Nickel-Doped Copper Oxide as an Efficient Electrocatalyst toward Water Oxidation Reaction

Production of hydrogen through water splitting is one of the green and the most practical solutions to cope with the energy crisis and greenhouse effect. However, oxygen evolution reaction (OER) being a sluggish step, the use of precious metal-based catalysts is the main impediment toward the viability of water splitting. In this work, amorphous copper oxide and doped binary- and ternary-metal oxides (containing CoII, NiII, and CuII) have been prepared on the surface of fluorine-doped tin oxide by a facile electrodeposition route followed by thermal treatment. The fabricated electrodes have been employed as efficient binder-free OER electrocatalysts possessing a high electrochemical surface area due to their amorphous nature. The cobalt-nickel-doped copper oxide (ternary-metal oxide)-based electrode showed promising OER activity with a high current density of 100 mA cm-2 at 1.65 V versus RHE that escalates to 313 mA cm-2 at 1.76 V in alkaline media at pH 14. The high activity of the ternary-metal oxide-based electrode was further supported by a smaller semicircle in the Nyquist plot. Furthermore, all metal-oxide-based electrodes offered high stability when tested for continuous production of oxygen for 50 h. This work highlights the synthesis of efficient and cost-effective amorphous metal-based oxide catalysts to execute electrocatalytic OER employing an electrodeposition approach.

Regulation of Morphology and Electronic Structure of NiSe2 by Fe for High Effective Oxygen Evolution Reaction

With the development of hydrogen-energy economy, it is urgent for researchers to explore high effective non-noble metal electrocatalysts for oxygen evolution reaction (OER). Nickel-based selenides have good conductivity and easy to regulate, which make them to be a promising OER electrocatalysts. Hence, many researchers engineering the structure of Nickel-based selenides to further improve the OER performance. In this paper, NixFe_1-x Se₂ porous-nano-microspheres with different ratio were synthesized. Results confirm that Fe not only affects the number of active sites in NiSe₂ , but also affects the intrinsic activity by forming lattice defects. Besides, introduction of Fe can change the redox ability of Ni cation and Se anion, thus, reducing the average valence state of Ni cation in NiOOH. As a result, the current density of OER is improved remarkably. When the current density reaches 10 mA cm^-2 , the overpotential is only 285 mV.

Activation of NLRP3 inflammasome in hepatocytes after exposure to cobalt nanoparticles: The role of oxidative stress

With the increased use of nanomaterials and increased exposure of humans to various nanomaterials, the potential health effects of nanomaterials cannot be ignored. The hepatotoxicity of cobalt nanoparticles (Nano-Co) is largely unknown and the underlying mechanisms remain obscure. The purpose of this study was to exam the hepatotoxicity induced by Nano-Co and its potential mechanisms. Our results showed that exposure of human fetal hepatocytes L02 to Nano-Co caused a dose- and a time-dependent cytotoxicity. Besides the generation of reactive oxygen species (ROS) and mitochondrial reactive oxygen species (mtROS), exposure to Nano-Co also caused activation of NOD-like receptor protein 3 (NLRP3) inflammasome in hepatocytes. After silencing NLRP3, one component of NLRP3 inflammasome, expression by siRNA strategy, we found that upregulation of NLRP3-related proteins was abolished in hepatocytes exposed to Nano-Co. Using antioxidants to scavenge ROS and mtROS, we demonstrated that Nano-Co-induced mtROS generation was related to Nano-Co-induced NLRP3 inflammasome activation. Our findings demonstrated that Nano-Co exposure may promote intracellular oxidative stress damage, and mtROS may mediate the activation of NLRP3 inflammasome in hepatocytes exposed to Nano-Co, suggesting an important role of ROS/NLRP3 pathway in Nano-Co-induced hepatotoxicity. These results provide scientific insights into the hepatotoxicity of Nano-Co and a basis for the prevention and treatment of Nano-Co-induced cytotoxicity.

Sulfur vacancy-tailored NiCo2S4 nanosheet arrays for the hydrogen evolution reaction at all pH values

Sulfur vacancy-tailored NiCo₂S₄ nanosheet arrays as efficient electrocatalysts for the hydrogen evolution reaction at all pH values.

Amorphous CoFe(OH)x hollow hierarchical structure: an efficient and durable electrocatalyst for oxygen evolution reaction

Amorphous CoFe(OH)_x hollow hierarchical microspheres are fabricated by using a polyhedral Cu₂O template. CoFe(OH)_x shows excellent OER activity and long-term durability due to its unique hollow hierarchical structure and composition.

Amorphous Catalysts and Electrochemical Water Splitting: An Untold Story of Harmony

In the near future, sustainable energy conversion and storage will largely depend on the electrochemical splitting of water into hydrogen and oxygen. Perceiving this, countless research works focussing on the fundamentals of electrocatalysis of water splitting and on performance improvements are being reported everyday around the globe. Electrocatalysts of high activity, selectivity, and stability are anticipated as they directly determine energy- and cost efficiency of water electrolyzers. Amorphous electrocatalysts with several advantages over crystalline counterparts are found to perform better in electrocatalytic water splitting. There are plenty of studies witnessing performance enhancements in electrocatalysis of water splitting while employing amorphous materials as catalysts. The harmony between the flexibility of amorphous electrocatalysts and electrocatalysis of water splitting (both the oxygen evolution reaction [OER] and the hydrogen evolution reaction [HER]) is one of the untold and unsummarized stories in the field of electrocatalytic water splitting. This Review is devoted to comprehensively discussing the upsurge of amorphous electrocatalysts in electrochemical water splitting. In addition to that, the basics of electrocatalysis of water splitting are also elaborately introduced and the characteristics of a good electrocatalyst for OER and HER are discussed.

Electrodeposition at Highly Negative Potentials of an Iron-Cobalt Oxide Catalyst for Use in Electrochemical Water Splitting

Earth-abundant transition metal-based catalysts have been extensively investigated for their applicability in water electrolysers to enable overall water splitting to produce clean hydrogen and oxygen. In this study a Fe-Co based catalyst is electrodeposited in 30 seconds under vigorous hydrogen evolution conditions to produce a high surface area material that is active for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). This catalyst can achieve high current densities of 600 mAcm^-2 at an applied potential of 1.6 V (vs RHE) in 1 M NaOH with a Tafel slope value of 48 mV dec^-1 for the OER. In addition, the HER can be facilitated at current densities as high as 400 mA cm^-2 due to the large surface area of the material. The materials were found to be predominantly amorphous but did contain crystalline regions of CoFe₂ O₄ which became more evident after the OER indicating interesting compositional and structural changes that occur to the catalyst after an electrocatalytic reaction. This rapid method of creating a bimetallic oxide electrode for both the HER and OER could possibly be adopted to other bimetallic oxide systems suitable for electrochemical water splitting.

One-step electrodeposition of AuNi nanodendrite arrays as photoelectrochemical biosensors for glucose and hydrogen peroxide detection

A novel nonsemiconductor photoelectrochemical biosensor was first constructed using the unique plasmonic AuNi nanodendrite arrays. The AuNi nanodendrite arrays were rapidly prepared by a one-step electrodeposition method using the porous anodic aluminum templates. Owing to its hierarchical structure with abundant active sites, the synergistic catalytic of Au and Ni can be better exploited. These plasmonic AuNi nanodendrite arrays display exceptional photoelectrocatalytic activities for glucose oxidation and hydrogen peroxide reduction reaction under visible light illumination. Specifically, the detection sensitivity for glucose (3.7277 mA mM^-1 cm^-2) under illumination is about 3.3 folds improvement than in the dark (1.1287 mA mM^-1 cm^-2), together with high accuracy and low detection limit of 3 μM. The markedly enhanced performance of AuNi nanodendrite arrays can be attributed to its hierarchical structure with abundant active sites and plasmonic effect of Au with strong absorption band in visible region. Such a newly developed method via the facile and low-cost route is of great significance in designing the plasmon-aided photoelectrochemical biosensors.

Water Oxidation Catalysts: The Quest for New Oxide-Based Materials

The expected shortage of fossil fuels as well as the accompanying climate change are among the major challenges of the 21st century. A global shift to a sustainable energy landscape is, therefore, of utmost importance. Over the past few years, solar technologies have entered the energy market and have paved the way to replace fossil-based energy sources, in the long term. In particular, electrochemical solar-to-hydrogen technologies have attracted a lot of interest—not only in academia, but also in industry. Solar water splitting (artificial photosynthesis) is one of the most active areas in contemporary materials and catalysis research. The development of low-cost, efficient, and stable water oxidation catalysts (WOCs) remains crucial for artificial photosynthesis applications, because WOCs still represent a major economical and efficient bottleneck. In the following, we summarize recent advances in water oxidation catalysts development, with selected examples from 2016 onwards. This condensed survey demonstrates that the ongoing quest for new materials and informed catalyst design is a dynamic and rapidly developing research area.

Monitoring compositional changes in Ni(OH)2 electrocatalysts employed in the oxygen evolution reaction

Relating morphology and compositional changes spatially across a catalyst is important for understanding the active site involved in a reaction which is studied here for the OER at Ni(OH)₂.

Self-supported bimetallic Ni-Co compound electrodes for urea- and neutralization energy-assisted electrolytic hydrogen production

Hydrogen represents one of the most promising renewable energy sources for next generation energy systems, however, its large scale production is high cost and high energy. A proof-of-concept alkaline-acid electrolyzer is reported here that can significantly reduce the amount of electrical energy consumed in electrolytic hydrogen production, implemented by the development of self-supported bimetallic Ni-Co compound electrodes used as the anode and cathode, respectively, where a urea oxidation reaction (UOR) occurs at the alkaline Ni_0.67Co_0.33(OH)₂ nanosheet anode, coupled to the hydrogen evolution reaction (HER) at the acidic Ni_0.67Co_0.33S₂ cathode. The asymmetric-electrolyte electrolyzer can efficiently harvest two kinds of energies, i.e. electrochemical neutralization energy (ENE) and electrochemical urea oxidation energy, to assist electrolytic hydrogen production using waste urea, acid, and base. The as-designed electrolyzer can deliver a current density of 10 mA cm^-2 for electrolytic H₂ generation with a rather low applied voltage of 0.54 V, with the potential to use up waste urea, acid and base.

Galvanic Replacement of Electrochemically Restructured Copper Electrodes with Gold and Its Electrocatalytic Activity for Nitrate Ion Reduction

The electrochemical formation of nanostructured materials is a cost effective route to creating substrates that can be employed in a variety of applications. In this work the surface of a copper electrode was electrochemically restructured in an alkaline solution containing ethanol as an additive to modify the surface morphology, and generate a Cu/Cu₂O surface, which is known to be active for the electrocatalytic reduction of environmentally harmful nitrate ions. To increase the activity of the nanostructured surface it was decorated with gold prisms through a facile galvanic replacement approach to create an active Cu/Cu₂O/Au layer. The surface was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, as well as electrochemical techniques. It was found that the presence of recalcitrant oxides, and Au was beneficial for the increased activity compared to unmodified copper and undecorated restructured copper and was consistent with the incipient hydrous oxide adatom mediator model of electrocatalysis. This approach to generating nanostructured metal/metal oxide surfaces that can be galvanically replaced to create these types of composites may have other applications in the area of electrocatalysis.

In Situ Electrodeposition of Cobalt Sulfide Nanosheet Arrays on Carbon Cloth as a Highly Efficient Bifunctional Electrocatalyst for Oxygen Evolution and Reduction Reactions

As one of the advanced cobalt-based materials, cobalt sulfides with novel architecture have attracted huge interest due to the low cost, easy availability, and promising bifunctional activity for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which is essential for next-generation energy storage devices. Herein, we demonstrated a facile and clean electrochemical technique to directly synthesize CoS nanosheets with high purity onto the surface of carbon cloth, and a quick thermal treatment was performed to further improve the catalytic performance (CoS-A). This novel electrochemical technique avoids the use of the binder, surfactant, and other organic additives, which may cause poor electric conductivity as well as undesirable surface wettability, exhibiting great potential of the large-scale applications. The obtained CoS-A exhibits a superior electrocatalytic performance for the OER and ORR, with a high ORR current density (-1.51 mA cm^-2 at 0.2 V), considerable OER current density (148 mA cm^-2 at 1.9 V), and excellent durability in continuous measurement for over 12 h. The approach offers a powerful yet simple method to control the phase, composition, and morphology of a highly active CoS catalyst, which provides a new idea for the design of high-performance catalysts.

Mo2C-Ni-modified nitrogen-doped carbon nanofiber toward efficient hydrogen evolution reaction

We have synthesized a fibroid electrocatalyst (Mo₂C-Ni@N-CNF) using a facile template-directed hydrothermal method which exhibited favourable hydrogen evolution reaction activity.