A facile and efficient strategy to gram-scale preparation of composition-controllable Ni-Fe LDHs nanosheets for superior OER catalysis

High-value utilization of Cr-containing sludge: Eco-friendly and ultra-low-cost electrocatalyst for efficient OER in alkaline media from Cr-containing sludge

Economically sustainable development requires more viable waste recycling solutions. In this context, we address the problem of utilizing chromium-containing sludge, a prevalent and environmentally hazardous waste. Meanwhile, sustainable energy development must develop ecology-friendly and low-cost electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. Herein, we report an ultra-low-cost electrocatalyst from chromium-containing sludge. The optimum preparation conditions are determined by optimizing the calcination temperature and the loading of nickel acetylacetonate. The optimized catalyst delivers excellent stability and outstanding OER activity with overpotentials of 320 mV at 10 mA cm-2 in alkaline media. Density functional theory calculations reveal that the energy barrier of OER is decreased because of the catalyst's heterogeneous structure arrangement and confirm the influence of chromium on performance improvement. The concept of "turning waste into treasure" stimulates the search for methods to process Cr-containing waste and produce low-cost, high-performance electrocatalysts.

Recent Progress of Transition Metal Compounds as Electrocatalysts for Electrocatalytic Water Splitting

Hydrogen has enormous commercial potential as a secondary energy source because of its high calorific value, clean combustion byproducts, and multiple production methods. Electrocatalytic water splitting is a viable alternative to the conventional methane steam reforming technique, as it operates under mild conditions, produces high-quality hydrogen, and has a sustainable production process that requires less energy. Electrocatalysts composed of precious metals like Pt, Au, Ru, and Ag are commonly used in the investigation of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Nevertheless, their limited availability and expensive cost restrict practical use. In contrast, electrocatalysts that do not contain precious metals are readily available, cost-effective, environmentally friendly, and possess electrocatalytic performance equal to that of noble metals. However, considerable research effort must be devoted to create cost-effective and high-performing catalysts. This article provides a comprehensive examination of the reaction mechanism involved in electrocatalytic water splitting in both acidic and basic environments. Additionally, recent breakthroughs in catalysts for both the hydrogen evolution and oxygen evolution reactions are also discussed. The structure-activity relationship of the catalyst was deep-going discussed, together with the prospects of current obstacles and potential for electrocatalytic water splitting, aiming at provide valuable perspectives for the advancement of economical and efficient electrocatalysts on an industrial scale.

A three-dimensional flower-like NiCo-layered double hydroxide grown on nickel foam with an MXene coating for enhanced oxygen evolution reaction electrocatalysis

Electrolysis of water is currently one of the cleanest and most efficient ways to produce high-purity hydrogen. The oxygen evolution reaction (OER) at the anode of electrolysis is the key factor affecting the reaction efficiency, which involves the transfer of four electrons and can slow down the overall reaction process. In this work, using nickel foam coated with MXene (Ti3C2T x ) as the carrier, a three-dimensional flower-shaped layered double hydroxide (NiCo-LDH) is grown on Ti3C2T x by a hydrothermal method to fabricate a NiCo-LDH/Ti3C2T x /NF hybrid electrocatalyst for enhanced OER performance. The results reveal that the hybrid electrocatalyst has excellent OER activity in alkaline solution, in which a low overpotential of 223 mV and a small Tafel slope of 47.2 mV dec-1 can be achieved at a current density of 100 mA cm-2. The interface interaction and charge transfer between Ti3C2T x and NiCo-LDH can accelerate the electron transfer rate during the redox process and improve the catalytic activity of the overall reaction. This NiCo-LDH/Ti3C2T x /NF hybrid electrocatalyst may have important research significance and great application potential in catalytic electrolysis of water.

Formation of graphene encapsulated cobalt–iron phosphide nanoneedles as an attractive electrocatalyst for overall water splitting

Hierarchical CoFe–P nanoneedles encapsulated in the graphene texture are fabricated for water splitting applications.

Improvement of Trisodium Citrate-Modified NiFe-Layered Double Hydroxide Nanosheets with Carbon Black for Oxygen Evolution Reaction

The pursuit of highly active and cost-effective catalysts toward oxygen evolution reaction (OER) is a crucial strategy to resolve the imminent energy crisis. NiFe layered double hydroxide (NiFe LDH) is acknowledged as one of the most promising OER electrocatalysts in alkaline electrolytes. Herein, we report a novel stepwise approach to synthesize NiFe LDHs materials merging with carbon black (CB) via trisodium citrate (TC), modifying toward OER. Benefiting from the inimitable wrapped structure, the decreased size of porous nanosheets and the superconductivity of CB substrate, NiFe LDHs/CB-TC presents excellent catalytic features with a comparative overpotential (236 mV at 10 mA cm−2) and an ultralow Tafel slope (31 mV dec−1), which are almost lower than those of advanced catalysts associated with expensive carbonaceous materials. Therefore, it is expected that such a high-activity and low-cost material can be a promising catalyst employed for the electrochemical energy storage and conversion systems.

3D amorphous NiFe LDH nanosheets electrodeposited on in situ grown NiCoP@NC on nickel foam for remarkably enhanced OER electrocatalytic performance

NiFe LDH (layered double hydroxide) is currently attracting increasing attention as a type of promising electrocatalyst for oxygen evolution reaction (OERs); however, the biggest obstacle to its large-scale practical application is its poor conductivity and limited active sites. Herein, we report a three-dimensional NiFe LDH with high conductivity and dense active sites, where amorphous NiFe LDH nanosheets are directly electrodeposited on the surface of a hierarchical porous NiCoP@NC derived from the calcination and phosphorization of metal-organic frameworks (ZIF-67) in situ grown on nickel foam. Based on the 3D porous structure, abundant exposed active sites, fast electron and mass transfer rates and strong synergetic effects between NiCoP@NC and NiFe LDH, the resultant NiFe LDH/NiCoP@NC/NF catalysts exhibited significantly enhanced OER catalytic performances compared with NiFe LDH on nickel foam and most of the reported NiFe LDH-based catalysts: a low overpotential of 210 mV for yielding a current density of 10 mA cm-2, an extremely small Tafel slope (35 mV dec-1) and excellent durability. For overall water splitting, with NiFe LDH/NiCoP@NC/NF as the anode and NiCoP@NC/NF as the cathode, the assembled two-electrode system only required 1.54 V to obtain a stable current density of 10 mA cm-2 in 1 M KOH for at least 40 h. This research provided a simple and facile way to develop non-noble-metal oxygen evolution catalysts for replacing high-cost noble metal catalysts.

Recent Progresses in Electrocatalysts for Water Electrolysis

Abstract

The study of hydrogen evolution reaction and oxygen evolution reaction electrocatalysts for water electrolysis is a developing field in which noble metal-based materials are commonly used. However, the associated high cost and low abundance of noble metals limit their practical application. Non-noble metal catalysts, aside from being inexpensive, highly abundant and environmental friendly, can possess high electrical conductivity, good structural tunability and comparable electrocatalytic performances to state-of-the-art noble metals, particularly in alkaline media, making them desirable candidates to reduce or replace noble metals as promising electrocatalysts for water electrolysis. This article will review and provide an overview of the fundamental knowledge related to water electrolysis with a focus on the development and progress of non-noble metal-based electrocatalysts in alkaline, polymer exchange membrane and solid oxide electrolysis. A critical analysis of the various catalysts currently available is also provided with discussions on current challenges and future perspectives. In addition, to facilitate future research and development, several possible research directions to overcome these challenges are provided in this article.

Graphical Abstract

Encapsulation of Ni/Fe3O4 heterostructures inside onion-like N-doped carbon nanorods enables synergistic electrocatalysis for water oxidation

The rational modulation of composition and structure is critical for the development of robust and efficient oxygen evolution reaction (OER) catalysts for water splitting. In this study, an onion-like N-doped carbon nanorods hybrid (denoted as ONC) with encapsulated Ni/Fe₃O₄ heterostructures has been fabricated by the pyrolysis of an NiFe-based coordination polymer under a N₂ atmosphere. The nanorod-like morphology is transferred from the polymer to the hybrids and generates ONC nanolayers encapsulated with core-shell Ni/Fe₃O₄ nanostructures. The synergistic effects between the ONC layers and the encapsulated Ni/Fe₃O₄ heterostructures result in high electronic conductivity due to the nitrogen-doped carbon with an appropriate level of defects and enlarged electrochemical surface area due to the well-defined mesoporous morphology. Compared with Ni@ONC, Fe₃O₄@ONC, NiFe₂O₄ and commercial RuO₂ electrocatalysts, the as-prepared Ni/Fe₃O₄@ONC exhibits extraordinary electrocatalytic activity for water oxidation with an overpotential of merely 296 mV at 10 mA cm^-2 and a small Tafel slope of 61 mV dec^-1. This Ni/Fe₃O₄@ONC OER catalyst highlights the great potential of integrating hetero-composite nanocatalysts with hetero-atom doped nanocarbon supports for the development of high-performance electrocatalysts for renewable energy applications.

Durable oxygen evolution reaction of one dimensional spinel CoFe2O4 nanofibers fabricated by electrospinning

One dimensional spinel CoFe₂O₄ nanofibers were synthesized via the electrospinning technique. The nanofibers were calcined at different temperatures. All CoFe₂O₄ nanofibers show excellent oxygen evolution reaction (OER) performance. The nanofibers calcined at 750 °C have a multi-particle nanochain structure. The nanochain exhibits excellent catalytic performance for OER in 1 M KOH (pH = 14) producing a current density of 10 mA cm⁻² at an overpotential of 0.34 V, and the small onset potential of 1.32 V versus RHE, better than that of the commercial Ir/C (20%) catalyst. Furthermore, the stability of CoFe₂O₄ multi-particle nanochains toward the OER decreases by only 0.78% even after a long period of 80 000 s. Our finding suggests that CoFe₂O₄ nanofibers with a multi-particle nanochain structure could serve as a new group of OER electrocatalysts with excellent performance.

One dimensional spinel CoFe₂O₄ nanofibers were synthesized via the electrospinning technique.