Electrodeposited Amorphous Tungsten‐doped Cobalt Oxide as an Efficient Catalyst for the Oxygen Evolution Reaction

Thin film of amorphous tungsten‐doped cobalt oxide (W:CoO) was successfully grown on a conducting electrode via an electrochemical oxidation process employing a [Co(WS₄)₂]^2? deposition bath. The W:CoO catalyst displays an attractive performance for the oxygen evolution reaction in an alkaline solution. In an NaOH solution of pH 13, W:CoO operates with a moderate onset overpotential of 230 mV and requires 320 mV overpotential to generate a catalytic current density of 10 mA cm^?2. A low Tafel slope of 45 mV decade^?1 was determined, indicating a rapid O₂‐evolving kinetics. The as‐prepared W:CoO belongs to the best cobalt oxide‐based catalysts ever reported for the oxygen evolution (OER) reaction.     

Iron–Cobalt Phosphomolybdate with High Electrocatalytic Activity for Oxygen Evolution Reaction

Iron–cobalt phosphomolybdate (FeCoPM₁₂) nanoparticles, which are highly efficient catalytic materials for the oxygen evolution reaction (OER), were fabricated through a coprecipitation route. Compared with iron–cobalt hydroxide and state‐of‐the‐art RuO₂ electrocatalysts, the as‐prepared FeCoPM₁₂ sample exhibited robust OER catalytic activity with a low overpotential of 258 mV at a current density of 10 mA cm⁻² and a small Tafel slope of 33 mV dec⁻¹. Moreover, the as‐synthesized sample presented preferable stability and after 10 h at 1.52 V the current density degraded by merely 8.3 %. This is ascribed to the high electrochemical stability and small porous structure of FeCoPM₁₂, which provide effective electron transmission and improve the catalytic performance for OER in alkaline media.     

Interface‐Engineered Ni(OH)2/β‐like FeOOH Electrocatalysts for Highly Efficient and Stable Oxygen Evolution Reaction

Iron‐based (oxy)hydroxides are especially attractive electrocatalysts for the oxygen evolution reaction (OER) owing to their earth abundance, low cost, and nontoxicity. However, poor OER kinetics on the surface restricts the performance of the FeOOH electrocatalyst. Herein, a highly efficient and stable Ni(OH)₂/β‐like FeOOH electrocatalyst is obtained by facile electroactivation treatment. The activated Ni(OH)₂/β‐like FeOOH sample indicates an overpotential of 300 mV at 10 mA cm⁻² for the OER, and no clear current decay after 50 h of testing; this is comparable to the most efficient nickel‐ and cobalt‐based electrocatalysts on planar substrates. Furthermore, studies suggest that β‐like FeOOH plays a key role in remarkably enhancing the performance during the electroactivation process owing to its metastable tunnel structure with a lower barrier for interface diffusion of Ni²⁺ ions between the bilayer electrocatalyst. This study develops a new strategy to explore efficient and low‐cost electrocatalysts and deepens understanding of bilayer electrocatalysts for the OER.     

Strong‐Coupled Cobalt Borate Nanosheets/Graphene Hybrid as Electrocatalyst for Water Oxidation Under Both Alkaline and Neutral Conditions

Developing highly active catalysts for the oxygen evolution reaction (OER) is of paramount importance for designing various renewable energy storage and conversion devices. Herein, we report the synthesis of a category of Co‐Pi analogue, namely cobalt‐based borate (Co‐B_i) ultrathin nanosheets/graphene hybrid by a room‐temperature synthesis approach. Benefiting from the high surface active sites exposure yield, enhanced electron transfer capacity, and strong synergetic coupled effect, this Co‐B_i NS/G hybrid shows high catalytic activity with current density of 10 mA cm^?2 at overpotential of 290 mV and Tafel slope of 53 mV dec^?1 in alkaline medium. Moreover, Co‐B_i NS/G electrocatalysts also exhibit promising performance under neutral conditions, with a low onset potential of 235 mV and high current density of 14.4 mA cm^?2 at 1.8 V, which is the best OER performance among well‐developed Co‐based OER electrocatalysts to date. Our finding paves a way to develop highly active OER electrocatalysts.     

Metallic Co4N Porous Nanowire Arrays Activated by Surface Oxidation as Electrocatalysts for the Oxygen Evolution Reaction

Designing highly efficient electrocatalysts for oxygen evolution reaction (OER) plays a key role in the development of various renewable energy storage and conversion devices. In this work, we developed metallic Co₄N porous nanowire arrays directly grown on flexible substrates as highly active OER electrocatalysts for the first time. Benefiting from the collaborative advantages of metallic character, 1D porous nanowire arrays, and unique 3D electrode configuration, surface oxidation activated Co₄N porous nanowire arrays/carbon cloth achieved an extremely small overpotential of 257 mV at a current density of 10 mA cm⁻², and a low Tafel slope of 44 mV dec⁻¹ in an alkaline medium, which is the best OER performance among reported Co‐based electrocatalysts to date. Moreover, in‐depth mechanistic investigations demonstrate the active phases are the metallic Co₄N core inside with a thin cobalt oxides/hydroxides shell during the OER process. Our finding introduces a new concept to explore the design of high‐efficiency OER electrocatalysts.     

Non‐3d Metal Modulation of a Cobalt Imidazolate Framework for Excellent Electrocatalytic Oxygen Evolution in Neutral Media

Cobalt imidazolate frameworks are classical electrocatalysts for the oxygen evolution reaction (OER) but suffer from the relatively low activity. Here, a non‐3d metal modulation strategy is presented for enhancing the OER activity of cobalt imidazolate frameworks. Two isomorphous frameworks [Co₄(MO₄)(eim)₆] (M=Mo or W, Heim=2‐ethylimidazole) having Co(eim)₃(MO₄) units and high water stabilities were designed and synthesized. In different neutral media, the Mo‐modulated framework coated on a glassy carbon electrode shows the best OER performances (1 mA cm^?2 at an overpotential of 210 mV in CO₂‐saturated 0.5 m KHCO₃ electrolyte and 2/10/22 mA cm^?2 at overpotential of 388/490/570 mV in phosphate buffer solution) among non‐precious metal catalysts and even outperforms RuO₂. Spectroscopic measurements and computational simulations revealed that the non‐3d metals modulate the electronic structure of Co for optimum reactant/product adsorption and tailor the energy of rate‐determining step to a more moderate value.     

Multifunctional Active‐Center‐Transferable Platinum/Lithium Cobalt Oxide Heterostructured Electrocatalysts towards Superior Water Splitting

Designing cost‐effective and efficient electrocatalysts plays a pivotal role in advancing the development of electrochemical water splitting for hydrogen generation. Herein, multifunctional active‐center‐transferable heterostructured electrocatalysts, platinum/lithium cobalt oxide (Pt/LiCoO₂) composites with Pt nanoparticles (Pt NPs) anchored on LiCoO₂ nanosheets, are designed towards highly efficient water splitting. In this electrocatalyst system, the active center can be alternatively switched between Pt species and LiCoO₂ for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Specifically, Pt species are the active centers and LiCoO₂ acts as the co‐catalyst for HER, whereas the active center transfers to LiCoO₂ and Pt turns into the co‐catalyst for OER. The unique architecture of Pt/LiCoO₂ heterostructure provides abundant interfaces with favorable electronic structure and coordination environment towards optimal adsorption behavior of reaction intermediates. The 30 % Pt/LiCoO₂ heterostructured electrocatalyst delivers low overpotentials of 61 and 285 mV to achieve 10 mA cm^?2 for HER and OER in alkaline medium, respectively.     

Boosting electrochemical hydrogen evolution by coupling anodically oxidative dehydrogenation of benzylamine to benzonitrile

The electricity-driven water splitting acts as a promising pathway for renewable energy conversion and storage, yet anodic oxygen evolution reaction (OER) largely hinders its efficiency. Seeking the alternatives to OER exhibits the competitive advance to address this predicament. In this work, we show a more thermodynamically and kinetically favorable reaction, electrochemical oxidative dehydrogenation (EODH) of benzylamine to replace the conventional OER, catalyzed by a cobalt cyclotetraphosphate (Co₂P₄O₁₂) nanorods catalyst grown on nickel foam. This anodic reaction lowers the electricity input of 317 mV toward the desired current density of 100 mA/cm², together with a highly selective benzonitrile product of more than 97%. More specifically, when coupling it with cathodic hydrogen evolution reaction (HER), the proposed HER||benzylamine-EODH configuration only requires a cell voltage of 1.47 V@100 mA/cm², exhibiting an energy-saving up to 17% relative to conventional water splitting, as well as the near unit selectivity toward cathodic H₂ and anodic benzonitrile products.     

A Surface‐Oxide‐Rich Activation Layer (SOAL) on Ni2Mo3N for a Rapid and Durable Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is key to renewable energy technologies such as water electrolysis and metal–air batteries. However, the multiple steps associated with proton‐coupled electron transfer result in sluggish OER kinetics and catalysts are required. Here we demonstrate that a novel nitride, Ni₂Mo₃N, is a highly active OER catalyst that outperforms the benchmark material RuO₂. Ni₂Mo₃N exhibits a current density of 10 mA cm^?2 at a nominal overpotential of 270 mV in 0.1 m KOH with outstanding catalytic cyclability and durability. Structural characterization and computational studies reveal that the excellent activity stems from the formation of a surface‐oxide‐rich activation layer (SOAL). Secondary Mo atoms on the surface act as electron pumps that stabilize oxygen‐containing species and facilitate the continuity of the reactions. This discovery will stimulate the further development of ternary nitrides with oxide surface layers as efficient OER catalysts for electrochemical energy devices.     

Interface Engineering of MoS2/Ni3S2 Heterostructures for Highly Enhanced Electrochemical Overall‐Water‐Splitting Activity

To achieve sustainable production of H₂ fuel through water splitting, low‐cost electrocatalysts for the hydrogen‐evolution reaction (HER) and the oxygen‐evolution reaction (OER) are required to replace Pt and IrO₂ catalysts. Herein, for the first time, we present the interface engineering of novel MoS₂/Ni₃S₂ heterostructures, in which abundant interfaces are formed. For OER, such MoS₂/Ni₃S₂ heterostructures show an extremely low overpotential of ca. 218 mV at 10 mA cm^?2, which is superior to that of the state‐of‐the‐art OER electrocatalysts. Using MoS₂/Ni₃S₂ heterostructures as bifunctional electrocatalysts, an alkali electrolyzer delivers a current density of 10 mA cm^?2 at a very low cell voltage of ca. 1.56 V. In combination with DFT calculations, this study demonstrates that the constructed interfaces synergistically favor the chemisorption of hydrogen and oxygen‐containing intermediates, thus accelerating the overall electrochemical water splitting.     

Autologous Cobalt Phosphates with Modulated Coordination Sites for Electrocatalytic Water Oxidation

The correlation between metal coordination and electrocatalytic water oxidation performance is elusive in many cobalt‐based materials. Herein, we designed an ideal Co phosphate‐based platform to explore the effect of coordination environment on oxygen evolution reaction (OER) activity. The cobalt geometry was modulated from octahedral to tetrahedral by simple removal of water ligands in Co₃(PO₄)₂?8 H₂O. Other features except the coordination structure in the two autologous materials remain similar. The two analogues display the same OER kinetics, but the anhydrous Co₃(PO₄)₂ exhibits a greatly enhanced OER activity. On the basis of Raman and operando XAS results, the higher intrinsic activity of the Co tetrahedral sites is because they facilitate the formation of active high valent cobalt (hydr)oxide intermediates during OER. This work not only brings insights of OER on Co‐based electrocatalysts but also provides a reference system to study the effect of metal geometry on electrocatalysis.     

Grafting Molecular Cobalt‐oxo Cubane Catalyst on Polymeric Carbon Nitride for Efficient Photocatalytic Water Oxidation

In this work, we have successfully constructed a cobalt–oxo (Co^III₄O₄) cubane complex on polymeric carbon nitride (PCN) through pyridine linkage. The covalently grafted Co^III₄O₄ cubane units were uniformly distributed on the PCN surface. The product exhibited greatly enhanced photocatalytic activities for water oxidation under visible‐light irradiation. Further characterizations and spectroscopic analyses revealed that the grafted Co^III₄O₄ cubane units could effectively capture the photogenerated holes from excited PCN, lower the overpotential of oxygen evolution reaction (OER), and serve as efficient catalysts to promote the multi‐electron water oxidation process. This work provides new insight into the future development of efficient photocatalysts by grafting molecular catalysts for artificial photosynthesis.     

Cobalt Doped Titanium Dioxide Nanoparticles: Synthesis,Characterization and Electrocatalytic Study

In this work, green synthesis of cobalt doped titanium dioxide (Co‐TiO₂) has been carried out in aqueous medium using gelatin. The Co‐TiO₂ particles have been characterized using transmission electron microscopy (TEM), X‐ray diffraction (XRD), energy dispersive X‐ray (EDAX), FT‐IR spectroscopy and voltammetry techniques. XRD results show pure Co‐TiO₂ and TiO₂ powders with average crystallite size about 12 nm and 15 nm, respectively. Co loaded in TiO₂ hasn't influence crystalline structure. Moreover, efficient Co‐TiO₂‐based anode was fabricated by casting of the Co‐TiO₂ solution on glassy carbon electrode (Co‐TiO₂/GCE). The electrocatalysis of oxygen evolution reaction (OER) at Co‐TiO₂/GCE has been examined using linear scanning voltammetry (LSV) in alkaline media. The OER is significantly enhanced at Co‐TiO₂/GCE, as demonstrated by a negative shift in the LSV curve at the Co‐TiO₂/GCE compared to that obtained at the unmodified one. The value of energy saving of oxygen gas at a current density of 5 mA cm^?2 is 12.6 kW h kg^?1. The low cost as well as the marked stability of the modified electrode make it promising candidate in industrial water electrolysis process.     

A Molecular Approach to Manganese Nitride Acting as a High Performance Electrocatalyst in the Oxygen Evolution Reaction

The scalable synthesis of phase‐pure crystalline manganese nitride (Mn₃N₂) from a molecular precursor is reported. It acts as a superiorly active and durable electrocatalyst in the oxygen evolution reaction (OER) from water under alkaline conditions. While electrophoretically deposited Mn₃N₂ on fluorine tin oxide (FTO) requires an overpotential of 390 mV, the latter is substantially decreased to merely 270 mV on nickel foam (NF) at a current density of 10 mA cm^?2 with a durability of weeks. The high performance of this material is due to the rapid transformation of manganese sites at the surface of Mn₃N₂ into an amorphous active MnO_x overlayer under operation conditions intimately connected with metallic Mn₃N₂, which increases the charge transfer from the active catalyst surface to the electrode substrates and thus outperforms the electrocatalytic activity in comparison to solely MnO_x‐based OER catalysts.     

Mass‐Production of Mesoporous MnCo2O4 Spinels with Manganese(IV)‐ and Cobalt(II)‐Rich Surfaces for Superior Bifunctional Oxygen Electrocatalysis

A mesoporous MnCo₂O₄ electrode material is made for bifunctional oxygen electrocatalysis. The MnCo₂O₄ exhibits both Co₃O₄‐like activity for oxygen evolution reaction (OER) and Mn₂O₃‐like performance for oxygen reduction reaction (ORR). The potential difference between the ORR and OER of MnCo₂O₄ is as low as 0.83 V. By XANES and XPS investigation, the notable activity results from the preferred Mn^IV‐ and Co^II‐rich surface. The electrode material can be obtained on large‐scale with the precise chemical control of the components at relatively low temperature. The surface state engineering may open a new avenue to optimize the electrocatalysis performance of electrode materials. The prominent bifunctional activity shows that MnCo₂O₄ could be used in metal–air batteries and/or other energy devices.     

Spontaneous Synthesis of Silver‐Nanoparticle‐Decorated Transition‐Metal Hydroxides for Enhanced Oxygen Evolution Reaction

The fabrication of metal‐supported hybrid structures with enhanced properties typically requires external energy input, such as pyrolysis, photolysis, and electrodeposition. In this study, silver‐nanoparticle‐decorated transition‐metal hydroxide (TMH) composites were synthesized by an approach based on a spontaneous redox reaction (SRR) at room temperature. The SRR between silver ions and TMH provides a simple and facile route to establish effective and stable heterostructures that can enhance the oxygen evolution reaction (OER) activity. Ag@Co(OH)_x grown on carbon cloth exhibits outstanding OER activity and durability, even superior to IrO₂ and many previously reported OER electrocatalysts. Experimental and theoretical analysis demonstrates that the strong electronic interaction between Ag and Co(OH)₂ activates the silver clusters as catalytically OER active sites, effectively optimizing the binding energies with reacted intermediates and facilitating the OER kinetics.     

Electrodeposited Cobalt‐Phosphorous‐Derived Films as Competent Bifunctional Catalysts for Overall Water Splitting

One of the challenges to realize large‐scale water splitting is the lack of active and low‐cost electrocatalysts for its two half reactions: H₂ and O₂ evolution reactions (HER and OER). Herein, we report that cobalt‐phosphorous‐derived films (Co‐P) can act as bifunctional catalysts for overall water splitting. The as‐prepared Co‐P films exhibited remarkable catalytic performance for both HER and OER in alkaline media, with a current density of 10 mA cm^?2 at overpotentials of ?94 mV for HER and 345 mV for OER and Tafel slopes of 42 and 47 mV/dec, respectively. They can be employed as catalysts on both anode and cathode for overall water splitting with 100 % Faradaic efficiency, rivalling the integrated performance of Pt and IrO₂. The major composition of the as‐prepared and post‐HER films are metallic cobalt and cobalt phosphide, which partially evolved to cobalt oxide during OER.     

A Plasma‐Triggered O−S Bond and P−N Junction Near the Surface of a SnS2 Nanosheet Array to Enable Efficient Solar Water Oxidation

A photoelectrochemical (PEC) cell can split water into hydrogen and oxygen with the assistance of solar illumination. However, its application is still limited by excessive bulk carrier recombination and sluggish surface oxygen evolution reaction (OER) kinetics. Taking SnS₂ as an example, a promising layered optoelectronic semiconductor, Ar plasma treatment strategy was used to introduce a SnS/SnS₂ P?N heterojunction and O?S bond near the surface of a SnS₂ nanosheet array, simultaneously increasing the separation efficiency of photogenerated electron–hole pairs in the bulk and lowering the OER overpotential at the surface. The onset potential of the plasma‐treated SnS₂ nanosheet array shifts negatively to 0.16 V, and the photocurrent density at 1.23 V vs. RHE boosts to 2.15 mA cm^?2, which is 7 times that of pristine SnS₂. This work demonstrates a facile plasma treatment strategy to modulate the energy band structure and surface chemical states for improved PEC performance.     

Amorphous Nanocages of Cu‐Ni‐Fe Hydr(oxy)oxide Prepared by Photocorrosion For Highly Efficient Oxygen Evolution

Electrochemical water splitting requires efficient, low‐cost water oxidation catalysts to accelerate the sluggish kinetics of the water oxidation reaction. A rapid photocorrosion method is now used to synthesize the homogeneous amorphous nanocages of Cu‐Ni‐Fe hydr(oxy)oxide as a highly efficient electrocatalyst for the oxygen evolution reaction (OER). The as‐fabricated product exhibits a low overpotential of 224 mV on a glassy carbon electrode at 10 mA cm^?2 (even lower down to 181 mV when supported on Ni foam) with a Tafel slope of 44 mV dec^?1 for OER in an alkaline solution. The obtained catalyst shows an extraordinarily large mass activity of 1464.5 A g^?1 at overpotential of 300 mV, which is the highest mass activity for OER. This synthetic strategy may open a brand new pathway to prepare copper‐based ternary amorphous nanocages for greatly enhanced oxygen evolution.     

Carbon Dots Integrated NiCo2O4 Hierarchical Nanoneedle Arrays Supported on Ni Foam as Efficient and Stable Electrode for Hydrogen and Oxygen Evolution Reactions

The production of hydrogen and oxygen via water electrolysis has become a sustainable and encouraging pathway for the establishment of new energy sources. Herein, we report the successful growth of hierarchical NiCo₂O₄‐carbon dots (CDs) nanoneedle arrays supported on nickel foam through a simple and environmentally benign hydrothermal self‐assembly technique. The designed material acts as a binder free electrode and shows bifunctional electrocatalytic activity for both hydrogen evolution reaction (HER) as well as oxygen evolution reaction (OER) in alkaline medium. An electrocatalyst sample with an optimal loading of CDs (25 mg) requires a low overpotential of 146 mV to achieve a current density of 10 mA/cm² for the HER in an alkaline medium, whereas it requires an overpotential of 390 mV to achieve a current density of 50 mA/cm² for the OER in the same alkaline medium. The excellent electrocatalytic activities of the sample with loading of CD can be ascribed due to the presence of large number of exposed active sites offered by CD/NiCo₂O₄ and the enhanced electron transfer processes occurring as a result of hierarchical structure composed of three‐dimensional nickel foam and the NiCo₂O₄?CDs nanoneedle arrays. Thus, the synthesis method introduced in this present work is a facile and cost‐effective approach for the construction of bifunctional electrocatalysts with high reactivity and excellent durability.