High-efficiency NiCo layered double hydroxide electrocatalyst

We report several kinds of NiCo-LDH composites by a hydrothermal reaction and subsequent electrodeposition process. The prepared NiCo-LDH@PEDOT-200 sample shows an overpotential of 52 mV for the HER at 10 mA cm−2 in 1.0 M KOH.

Amorphous-crystalline FeNi2S4@NiFe-LDH nanograsses by molten salt as an industrially promising electrocatalyst for oxygen evolution

Inexpensive and accessible NiFe-based oxygen evolution reaction (OER) electrocatalyst are limited for practical industrial applications by its activity and stability under industrial conditions. Herein, FeNi2S4@NiFe-LDH heterostructure is constructed by molten...

Ce-Substituted Spinel CuCo2O4 Quantum Dots with High Oxygen Vacancies and Greatly Improved Electrocatalytic Activity for Oxygen Evolution Reaction

Exploring effective electrocatalysts for oxygen evolution reaction (OER) is a crucial requirement of many energy storage and transformation systems, involving fuel cells, water electrolysis, and metal-air batteries. Transition-metal oxides (TMOs) have attracted much attention to OER catalysts because of their earth abundance, tunable electronic properties, and so forth. Defect engineering is a general and the most important strategy to tune the electronic structure and control size, and thus improve their intrinsic activities. Herein, OER performance on spinel CuCo₂O₄ was greatly enhanced through cation substitution and size reduction. Ce-substituted spinel CuCe_δCo_2-δO_x (δ = 0.45, 0.5 and 0.55) nanoparticles in the quantum dot scale (2-8 nm) were synthesized using a simple and facile phase-transfer coprecipitation strategy. The as-prepared samples were highly dispersed and have displayed a low overpotential of 294 mV at 10 mA·cm^-2 and a Tafel slope of 57.5 mV·dec^-1, which outperform commercial RuO₂ and the most high-performance analogous catalysts reported. The experimental and calculated results all confirm that Ce substitution with an appropriate content can produce rich oxygen vacancies, tune intermediate absorption, consequently lower the energy barrier of the determining step, and greatly enhance the OER activity of the catalysts. This work not only provides advanced OER catalysts but also opens a general avenue to understand the structure-activity relationship of pristine TMO catalysts deeply in the quantum dot scale and the rational design of more efficient OER catalysts.

Promoting electrocatalytic overall water splitting by sulfur incorporation into CoFe-(oxy)hydroxide

The design and fabrication of highly cost-effective electrocatalysts with high activity, and stability to enhance the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has been considered to be one of the most promising approaches toward overall water splitting. In this study, sulfur-incorporated cobalt-iron (oxy)hydroxide (S-(Co,Fe)OOH) nanosheets were directly grown on commercial iron foam via galvanic corrosion and hydrothermal methods. The incorporation of sulfur into (Co,Fe)OOH results in superior catalytic performance and high stability in both the HER and OER conducted in 1 M KOH. The incorporation of sulfur enhanced the electrocatalytic activity by modifying the electronic structure and chemical states of (Co,Fe)OOH. An alkaline water electrolyzer for overall water splitting was fabricated using a two-electrode configuration utilizing the S-(Co,Fe)OOH bifunctional electrocatalyst in both the HER and OER. The fabricated electrolyzer outperformed a precious metal-based electrolyzer using Pt/C as the HER electrocatalyst and IrO2 as the OER electrocatalyst, which are the benchmark catalysts. This electrolyzer provides a lower potential of 1.641 V at 10 mA cm-2 and maintains 98.4% of its performance after 50 h of durability testing. In addition, the S-(Co,Fe)OOH-based electrolyzer successfully generated hydrogen under natural illumination upon its combination with a commercial silicon solar cell and exhibited a solar to hydrogen (STH) efficiency of up to 13.0%. This study shows that S-(Co,Fe)OOH is a promising candidate for application in the future renewable energy industry due to its high cost-effectiveness, activity, and stability during overall water splitting. In addition, the combination of a commercial silicon solar cell with an alkaline water electrolyzer has great potential for the production of hydrogen.

Optimization of Oxygen Evolution Reaction with Electroless Deposited Ni-P Catalytic Nanocoating

The low efficiency of water electrolysis mostly arises from the thermodynamic uphill oxygen evolution reaction. The efficiency can be greatly improved by rationally designing low-cost and efficient oxygen evolution anode materials. Herein, we report the synthesis of Ni-P alloys adopting a facile electroless plating method under mild conditions on nickel substrates. The relationship between the Ni-P properties and catalytic activity allowed us to define the best conditions for the electroless synthesis of highperformance Ni-P catalysts. Indeed, the electrochemical investigations indicated an increased catalytic response by reducing the thickness and Ni/P ratio in the alloy. Furthermore, the Ni-P catalysts with optimized size and composition deposited on Ni foam exposed more active sites for the oxygen evolution reaction, yielding a current density of 10 mA cm-2 at an overpotential as low as 335 mV, exhibiting charge transfer resistances of only a few ohms and a remarkable turnover frequency (TOF) value of 0.62 s-1 at 350 mV. The present study provides an advancement in the control of the electroless synthetic approach for the design and large-scale application of high-performance metal phosphide catalysts for electrochemical water splitting.

Selenium-induced NiSe2@CuSe2 hierarchical heterostructure for efficient oxygen evolution reaction

Electrochemical water splitting is widely studied in the hope of solving environmental deterioration and energy shortage. The design of inexpensive metal catalysts exhibiting desired catalytic performance and durable stability for efficient oxygen evolution is the pursuit of sustainable and clean energy fields. Herein, a three-dimensional (3D) flower-like NiSe₂ primary structure, modified with highly dispersed CuSe₂ nanoclusters as the secondary structure, is obtained by regulating the growth trend of the nanosheets. Benefiting from the metallicity of selenides and the formation of a heterogeneous interface, NiSe₂@CuSe₂/NF shows comparable performance toward the oxygen evolution reaction (OER) in an alkaline environment. Upon regulating the synthesis conditions, the catalyst exhibits its optimal performance with ultralow overpotential for the OER when the Ni/Cu molar ratio is 1 : 0.2 and the hydrothermal temperature and hydrothermal time are 200 °C and 6 h, respectively. It provides a current density of 10 mA cm^-2 when a potential of 201 mV is applied without iR compensation. In this work, the hierarchical heterostructures of NiSe₂ and CuSe₂ are synthesized, which exhibit high electrocatalytic activity towards the oxygen evolution reaction and provides a new possibility for the extensive application of copper-based compounds in advanced energy fields.

Structural and Interfacial Engineering of Ni2P/Fe3O4 Porous Nanosheet Arrays for Efficient Oxygen Evolution Reaction

Rational design of transition-metal phosphide (TMPs)-based electrocatalysts can effectively promote oxygen evolution reaction (OER). Herein, the novel efficient Ni₂P/Fe₃O₄ porous nanosheets arrays supported on Ni foam (Ni₂P/Fe₃O₄/NF) as alkaline OER catalysts were synthesized using structural and interfacial engineering. The three-dimensional (3D) porous hierarchical structure of Ni₂P/Fe₃O₄/NF provides abundant active sites for OER and facilitates the electrolyte diffusion of ions and O₂ liberation. Furthermore, the strong interfacial coupling and synergistic effect between Ni₂P and Fe₃O₄ modify the electronic structure, resulting in the enhanced intrinsic activity. Consequently, the optimized Ni₂P/Fe₃O₄/NF exhibits excellent OER performance with low overpotentials of 213 and 240 mV at 60 and 100 mA cm^-2 in 1.0 M KOH, respectively, better than the RuO₂/NF and most Ni/Fe-based OER catalysts. Impressively, it can maintain its catalytic activity for at least 20 h at 60 mA cm^-2. In addition, the relationship between the structure and performance is fully elucidated by the experimental characterizations, indicating that the metal oxyhydroxides in situ generated on the surface of catalysts are responsible for the high OER activity.

Discharge-Induced Enhancement of the Oxygen Evolution Reaction

The fundamental understanding of the surface reconstruction induced by the applied potential is of great significance for enhancing the oxygen evolution reaction (OER). Here, we show that a previously overlooked discharge current in the low applied potential region also leads to in situ electrochemical activation of a nitrogen-doped nickel oxyhydroxide surface. We exploit the fact that doping of heteroatoms weakens the surface structure, and hence, a weak discharge current originating from the capacitive nature of nickel oxyhydroxide has a strong structure-reforming ability to promote the formation of nitrogen and oxygen vacancies. The current density at 1.4 V (vs. Hg/HgO) can dramatically increase by as much as 31.3 % after discharge in the low applied potential region. This work provides insight into in situ enhancement of the OER and suggests that the low applied potential region must be a primary consideration in evaluating the origin of the activity of electrocatalysts.

NiFe Layered-Double-Hydroxide Nanosheet Arrays on Graphite Felt: A 3D Electrocatalyst for Highly Efficient Water Oxidation in Alkaline Media

It is of great importance to rationally design and develop earth-abundant nanocatalysts for high-efficiency water electrolysis. Herein, NiFe layered double hydroxide was in situ grown hydrothermally on a 3D graphite felt (NiFe LDH/GF) as a high-efficiency catalyst in facilitating the oxygen evolution reaction (OER). In 1.0 M KOH, NiFe LDH/GF requires a low overpotential of 214 mV to deliver a geometric current density of 50 mA cm^-2 (η_{50 mA cm^-2} = 214 mV), surpassing that NiFe LDH supported on a 2D graphite paper (NiFe LDH/GP; η_{50 mA cm^-2} = 301 mV). More importantly, NiFe LDH/GF shows good durability at 50 mA cm^-2 within 50 h of OER catalysis testing and delivers a faradaic efficiency of nearly 100% in the electrocatalysis of OER.

Fe, Ni-codoped W18O49 grown on nickel foam as a bifunctional electrocatalyst for boosted water splitting

Designing cost-effective bifunctional catalysts with high-performance and durability is of great significance for renewable energy systems. Herein, typical Fe, Ni-codoped W₁₈O₄₉/NF was prepared via a simple solvothermal method. The incorporation of Fe ions enhanced the electronic interaction and enlarged the electrochemically active surface area. The increased W⁴⁺ leads to a high proportion of unsaturated W[double bond, length as m-dash]O bonds, thus enhancing the adsorption capacity of water. The valence configuration of nickel (Ni) sites in such dual-cation doping is well adjusted, realizing a high proportion of trivalent Ni ions (Ni³⁺). Due to the orbital interactions, the Fe³⁺/Ni³⁺ ions and OER reaction intermediates exhibit strong orbital overlap. The positions of the valence band and conduction band are well modulated. As a result, the Fe, Ni-codoped W₁₈O₄₉/NF shows improved electrocatalytic activity, and achieves a low decomposition voltage of 1.58 V at 10 mA cm^-2 and retains long-time stability.

Novel synthesis of in situ CeOx nanoparticles decorated on CoP nanosheets for highly efficient electrocatalytic oxygen evolution

CoP nanosheets decorated by in-situ CeOx nanoparticles were designed through a novel two-step solvothermal-phosphating strategy, which act as an electrode exhibit excellent electrocatalytic performance toward OER in alkaline condition.

Hierarchical tube brush-like Co3S4@NiCo-LDH on Ni foam as a bifunctional electrocatalyst for overall water splitting

The Co3S4@NiCo-LDH/NF nanocomposite exhibits outstanding electrocatalytic performances toward both the HER and OER at high current densities, along with a remarkable durability.