The oxides of cobalt have recently been shown to be highly effective electrocatalysts for the oxygen evolution reaction (OER) under alkaline conditions. In general species such as Co3O4 and CoOOH have been investigated that often require an elevated temperature step during their synthesis to create crystalline materials. In this work we investigate the rapid and direct electrochemical formation of amorphous nanostructured Co(OH)2 on gold electrodes under room temperture conditions which is a highly active precursor for the OER. During the OER some conversion to crystalline Co3O4 occurs at the surface, but the bulk of the material remains amorphous. It is found that the underlying gold electrode is crucial to the materials enhanced performance and provides higher current density than can be achieved using carbon, palladium or copper support electrodes. This catalyst exhibits excellent activity with a current density of 10 mA cm-2 at an overpotential of 360 mV with a high turnover frequency of 2.1 s-1 in 1 M NaOH. A Tafel slope of 56 mV dec-1 at low overpotentials and a slope of 122 mV dec-1 at high overpotentials is consistent with the dual barrier model for the electrocatalytic evolution of oxygen. Significantly, the catalyst maintains excellent activity for up to 24 hr of continuous operation and this approach offers a facile way to create a highly effective and stable material.

Direct electrochemical formation of nanostructured amorphous Co(OH)2 on gold electrodes with enhanced activity for the oxygen evolution reaction.

Anion doping shows promising potential in optimizing the adsorption and desorption of reaction intermediates on the surface of NiFe-based layered double hydroxide (NiFe-LDH) for oxygen evolution reaction (OER). However, conventional doping methods are meticulous and complex. Hence, S-doped NiFe-LDH (S-NiFe-LDH-t-A) driven by short-time room-temperature electrochemical activation procedure is synthesized. The NiFe-LDH prefabricated by spontaneous substrate corrosion ensures large active surface area, exposed active sites and long-term robustness. Then moderate S doping electrochemically motivated is applied to the regulation of NiFe-LDH, which not only improves the bonding between metals and reaction intermediates but also induces decreased free energy, thus enhancing OER performance. Electrochemical measurements verified the low overpotential of 270 mV at 50 mA cm−2 and favorable durability for optimized S-NiFe-LDH-9-A benefited from the synergistic effect between NiFe-LDH and S species. This work provides a facile electrochemical activation strategy for anion doping, which show implications for the design of advanced catalysts.

S-doped nickel-iron hydroxides synthesized by room-temperature electrochemical activation for efficient oxygen evolution

The development of efficient oxygen electrocatalysts and understanding their underlying catalytic mechanism are of significant importance for the high-performance energy conversion and storage technologies. Herein, we report novel CoCu-based bimetallic metal-organic framework nanoboxes (CoCu-MOF NBs) as promising catalysts toward efficient electrochemical oxygen evolution reaction (OER), fabricated via a successive cation and ligand exchange strategy. With the highly exposed bimetal centers and the well-designed architecture, the CoCu-MOF NBs show excellent OER activity and stability, with a small overpotential of 271 mV at 10 mA cm-2 and a high turnover frequency value of 0.326 s-1 at an overpotential of 300 mV. In combination of quasi in situ X-ray absorption fine structure spectroscopy and density-functional theory calculations, the post-formed CoCu-based oxyhydroxide analogue during OER is believed to account for the high OER activity of CoCu-MOF NBs, where the electronic synergy between Co and neighbouring Cu atoms promotes the O-O bond coupling toward fast OER kinetics.

Synergetic Cobalt-Copper-Based Bimetal-Organic Framework Nanoboxes toward Efficient Electrochemical Oxygen Evolution.

Sparked by natural photosynthesis, solar photocatalysis using metal‐free graphitic carbon nitride (g‐C3N4) with appealing electronic structure has turned up as the most captivating technique to the quest for sustainable energy generation and pollution‐free environment. Nonetheless, low‐dimensional g‐C3N4 is thwarted from sluggish kinetics and rapid recombination of photogenerated carriers upon light irradiation. Among multifarious modification strategies, engineering 2D cocatalysts is anticipated to accelerate redox kinetics, augment active sites and ameliorate electron–hole separation of 2D g‐C3N4 for boosted activity thanks to its face‐to‐face contact surface. It is of timely and technological significance to review the 2D/2D interfaces with state‐of‐the‐art 2D cocatalysts, spanning from carbon‐containing to phosphorus‐containing, metal dichalcogenide, and other cocatalysts. Fundamental principles for each photocatalytic application will be introduced. Thereafter, the recent advances of 2D/2D cocatalyst‐mediated g‐C3N4 systems will be critically evaluated based on their interfacial engineering, emerging roles, and impacts toward stability and catalytic efficiency. Importantly, mechanistic insights into the charge dynamics and structure–performance relationship will be deciphered. Last, noteworthy research directions are prospected to deliver insightful ideas for future development of g‐C3N4. Overall, this review is anticipated to serve as a scaffold and cornerstone in designing dimensionality‐dependent 2D cocatalyst‐assisted g‐C3N4 toward renewable energy and ecologically green environment.

Tailor‐Engineered 2D Cocatalysts: Harnessing Electron–Hole Redox Center of 2D g‐C3N4 Photocatalysts toward Solar‐to‐Chemical Conversion and Environmental Purification

A highly active and stable hybrid electrocatalyst 3D hierarchical CoS₂ nanosheets incorporated with WS₂ (CoS₂@WS₂) has been developed via a one-step sulfurization method for the first time, where the contents of WS₂ can be adjusted easily. We first prove that the addition of small amounts of WS₂ enhances the hydrogen evolution reaction (HER) performance of CoS₂, and vice versa. In other words, we validated the symmetric synergy for the HER between the Co- and W-based sulfide hybrid catalysts. In addition, we confirmed that the formation of nanointerfaces of Co–S–W between CoS₂ and WS₂ was responsible for the excellent HER activity (an overpotential of −97.2 mV at −10 mA cm⁻², a small Tafel slope of 66.0 mV dec⁻¹, and prominent electrochemical stability) of the hybrid electrocatalyst CoS₂@WS₂.

Symmetric synergy of hybrid CoS₂–WS₂ electrocatalysts for the hydrogen evolution reaction

The latest development of CoOOH two-dimensional materials used as OER catalysts

Electrocatalytic decomposition of water is an effective method to solve the energy and environmental crisis brought about by fossil fuel combustion. Due to its low cost and abundant resources, non‐precious metal catalysts have achieved rapid development and are widely used in the electrolysis of water. Among these catalysts, WS2 is known as a potential candidate for water decomposition catalysts because of its unique physical and chemical properties and crystal structure. Therefore, we summarize the application of WS2 in the field of electrolysis water splitting. First, the crystal structure, the principle of HER/OER, and the performance evaluation parameters are introduced. Then it focuses on the preparation and structure control of WS2, the method, and the mechanism of performance optimization. Finally, the research on theoretical calculations of WS2 and a discussion about the opportunities and challenges of WS2 as electrocatalyst in the future are summarized. To improve the readability of this review, a concise overview at the end of each section gives some of the characteristics and trends of the studies in the corresponding part.

Recent Advances in Layered Tungsten Disulfide as Electrocatalyst for Water Splitting

As a new type of crystalline porous material, the imidazole zeolite framework (ZIF) has attracted widespread attention due to its ultra-high surface area, large pore volume, and unique advantage of easy functionalization. Developing different methods to control the shape and composition of ZIF is very important for its practical application as catalyst. In recent years, nano-ZIF has been considered an electrode material with excellent oxygen evolution reaction (OER) performance, which provides a new way to research electrolyzed water. This review focuses on the morphological engineering of the original ZIF-67 and its derivatives (core-shell, hollow, and array structures) through doping (cation doping, anion doping, and co-doping), derivative composition engineering (metal oxide, phosphide, sulfide, selenide, and telluride), and the corresponding single-atom catalysis. Besides, combined with DFT calculations, it emphasizes the in-depth understanding of actual active sites and provides insights into the internal mechanism of enhancing the OER and proposes the challenges and prospects of ZIF-67 based electrocatalysts. We summarize the application of ZIF-67 and its derivatives in the OER for the first time, which has significantly guided research in this field.

ZIF-67-based catalysts for oxygen evolution reaction

Anionic sulfur-modified FeNi-LDH at various Fe/Ni molar ratios for high-performance OER electrocatalysis

For the electrocatalytic oxygen evolution reaction (OER) in alkaline media, there is an urgent need to optimize the adsorption strength of OH*. Here, a flower-like hybrid of Cr-doped FeOOH/Ni(OH)2 was used as an OER catalyst with a low overpotential of 291 mV at 50 mA cm-2. The results showed that faster charge transfer was achieved at the electrode/solution interface during the OER process after the FeOOH/Ni(OH)2 was modified by Cr, which facilitates the rate-determining step of the Volmer reaction. Furthermore, the results of faradaic efficiency and X-ray photoelectron spectroscopy (XPS) measurements confirmed that the synergistic effect between the ternary metal and oxygen vacancies led to excellent OER performance. This work provides a new strategy for the preparation of high-efficiency and low-cost oxygen evolution electrocatalysts.

Hui Wen

Papers

The latest development of CoOOH two-dimensional materials used as OER catalysts

Recent Advances in Layered Tungsten Disulfide as Electrocatalyst for Water Splitting

ZIF-67-based catalysts for oxygen evolution reaction

Anionic sulfur-modified FeNi-LDH at various Fe/Ni molar ratios for high-performance OER electrocatalysis

Boosting the charge transfer of FeOOH/Ni(OH)2 for excellent oxygen evolution reaction via Cr modification.