Two-dimensional bimetallic phosphide ultrathin nanosheets as non-noble electrocatalysts for a highly efficient oxygen evolution reaction

Rational design and construction of hierarchical porous quasi-hexagonal Co2P nanosheets/Co heterostructures as highly efficient bifunctional electrocatalysts for overall water splitting

Constructing heterostructured electrocatalysts has proven effective in enhancing intrinsic catalytic activity. Herein, under guidance of theoretical calculations, hierarchical porous quasi-hexagonal Co2P nanosheets/Co heterostructures supported on carbon cloth (Co2P/Co/CC) with a high surface area were rationally designed and elaborately constructed through electroless Co plating, electrochemical oxidation, and phosphidation process, which showed significant electrocatalytic performance toward water electrolysis. Specifically, theoretical calculations revealed that the Co2P/Co heterostructure adjusted the electronic structure of Co2P and Co, reducing the energy barrier for target reactions and thereby boosting electrocatalytic activities for the hydrogen evolution reaction (HER). Notably, the typical Co2P/Co/CC catalyst demonstrated impressive HER performance, with low overpotentials of only 52 and 48 mV to achieve a current density of 10 mA/cm2 in 0.5 M H2SO4 and 1.0 M KOH solutions, respectively. The remarkable electrocatalytic performance of the catalyst can be attributed to the improved intrinsic activity resulting from the Co2P/Co heterostructures and the highly exposed active sites provided by the hierarchical porous structures. Furthermore, the Co2P/Co/CC catalyst exhibited excellent oxygen evolution reaction (OER) performance in alkaline electrolyte, requiring a low overpotential of only 306 mV to achieve a current density of 100 mA/cm2. Additionally, a two-electrode electrolyzer assembled with the Co2P/Co/CC electrodes achieved a current density of 10 mA/cm2 at a low cell voltage of 1.54 V and demonstrated excellent long-term stability. This work presents a novel and feasible strategy for constructing hierarchical heterostructured electrocatalysts that enable efficient water electrolysis. By combining rational design and theoretical guidance, our approach offers promising prospects for advancing the field of electrocatalysis and facilitating sustainable energy conversion.

State-of-the-Art Two-Dimensional Metal Phosphides for High Performance Lithium-ion Batteries: Progress and Prospects

Lithium-ion batteries (LIBs) with high energy density, long cycle life and safety have earned recognition as outstanding energy storage devices, and have been used in extensive applications, such as portable electronics and new energy vehicles. However, traditional graphite anodes deliver low specific capacity and inferior rate performance, which is difficult to satisfy ever-increasing demands in LIBs. Very recently, two-dimensional metal phosphides (2D MPs) emerge as the cutting-edge materials in LIBs due to their overwhelming advantages including high theoretical capacity, excellent conductivity and short lithium diffusion pathway. This review summarizes the up-to-date advances of 2D MPs from typical structures, main synthesis methods and LIBs applications. The corresponding lithium storage mechanism, and relationship between 2D structure and lithium storage performance is deeply discussed to provide new enlightening insights in application of 2D materials for LIBs. Several potential challenges and inspiring outlooks are highlighted to provide guidance for future research and applications of 2D MPs.

Selenium-transition metal supported on a mixture of reduced graphene oxide and silica template for water splitting

Exploration of economical, highly efficient, and environment friendly non-noble-metal-based electrocatalysts is necessary for hydrogen and oxygen evolution reactions (HER and OER) but challenging for cost-effective water splitting. Herein, metal selenium nanoparticles (M = Ni, Co & Fe) are anchored on the surface of reduced graphene oxide and a silica template (rGO-ST) through a simple one-pot solvothermal method. The resulting electrocatalyst composite can enhance mass/charge transfer and promote interaction between water molecules and electrocatalyst reactive sites. NiSe₂/rGO-ST shows a remarkable overpotential (52.5 mV) at 10 mA cm^-2 for the HER compared to the benchmark Pt/C E-TEK (29 mV), while the overpotential values of CoSeO₃/rGO-ST and FeSe₂/rGO-ST are 246 and 347 mV, respectively. The FeSe₂/rGO-ST/NF shows a low overpotential (297 mV) at 50 mA cm^-2 for the OER compared to RuO₂/NF (325 mV), while the overpotentials of CoSeO₃-rGO-ST/NF and NiSe₂-rGO-ST/NF are 400 and 475 mV, respectively. Furthermore, all catalysts indicate negligible deterioration, indicating better stability during the process of HER and OER after a stability test of 60 h. The water splitting system composed of NiSe₂-rGO-ST/NF||FeSe₂-rGO-ST/NF electrodes requires only ∼1.75 V at 10 mA cm^-2. Its performance is nearly close to that of a noble metal-based Pt/C/NF||RuO₂/NF water splitting system.

Constructing interface engineering and tailoring a nanoflower-like FeP/CoP heterostructure for enhanced oxygen evolution reaction

The inexpensive and highly efficient electrocatalysts toward oxygen evolution reaction (OER) in water splitting electrolysis have displayed promising practical applications to relieve energy crisis. Herein, we prepared a high-yield and structurally regulated bimetallic cobalt-iron phosphide electrocatalyst by a facile one-pot hydrothermal reaction and subsequent low-temperature phosphating treatment. The tailoring of nanoscale morphology was achieved by varying the input ratio and phosphating temperature. Thus, an optimized FeP/CoP-1-350 sample with the ultra-thin nanosheets assembled into a nanoflower-like structure was obtained. FeP/CoP-1-350 heterostructure displayed remarkable activity toward the OER with a low overpotential of 276 mV at a current density of 10 mA cm^-2, and a low Tafel slope of only 37.71 mV dec^-1. Long-lasting durability and stability were maintained with the current with almost no obvious fluctuation. The enhanced OER activity was attributed to the presence of copious active sites from the ultra-thin nanosheets, the interface between CoP and FeP components, and the synergistic effect of Fe-Co elements in the FeP/CoP heterostructure. This study provides a feasible strategy to fabricate highly efficient and cost-effective bimetallic phosphide electrocatalysts.

Enhanced Oxygen Evolution of a Magnetic Catalyst by Regulating Intrinsic Magnetism

The promotion of magnetic field on catalytic performance has attracted extensive attention. However, little research has been reported on the performance of the oxygen evolution reaction (OER) for the modulating intrinsic magnetism of the catalyst under a magnetic field. Herein, we adjusted the intrinsic magnetism of the Co_xNi_1-xFe₂O₄-nanosheet by adjusting the ratio of Co and Ni, and researched the relationship between the OER activity and the intrinsic magnetism. The results indicate that the CoFe₂O₄-nanosheet has the most OER activity increases in the magnetic field due to the optimal intrinsic magnetism. The required overpotential of CoFe₂O₄-nanosheet@NF to reach a current density of 10 mA cm^-2 was reduced by 21 mV under about 100 mT magnetic field compared with no magnetic field, and the degree of improvement of OER activity of different magnetic catalysts in the same magnetic field is positively correlated with the intrinsic magnetism of the catalyst. Therefore, magnetic field assistance provides a new, effective, and general strategy to improve the activity of electrodes for water splitting.

Fe-CoP/C composite nanoplate derived from 2D porphyrin MOF as an efficient catalyst for oxygen evolution reaction

The 2D Fe-CoP/C composite transformed from 2D PPF-5-Fe/Co MOF presents a high activity for the oxygen evolution reaction in alkaline media.

Electronic Modulation of Non-van der Waals 2D Electrocatalysts for Efficient Energy Conversion

The exploration of efficient electrocatalysts for energy conversion is important for green energy development. Owing to their high surface areas and unusual electronic structure, 2D electrocatalysts have attracted increasing interest. Among them, non-van der Waals (non-vdW) 2D materials with numerous chemical bonds in all three dimensions and novel chemical and electronic properties beyond those of vdW 2D materials have been studied increasingly over the past decades. Herein, the progress of non-vdW 2D electrocatalysts is critically reviewed, with a special emphasis on electronic structure modulation. Strategies for heteroatom doping, vacancy engineering, pore creation, alloying, and heterostructure engineering are analyzed for tuning electronic structures and achieving intrinsically enhanced electrocatalytic performances. Lastly, a roadmap for the future development of non-vdW 2D electrocatalysts is provided from material, mechanism, and performance viewpoints.

Single-unit-cell-thick layered electrocatalysts: from synthesis to application

Electrocatalysts are critical for water splitting, carbon dioxide reduction, and zinc-air battery. However, the low-exposed surface areas of bulk electrocatalysts usually limit the complete utilization of active sites. Ultrathin electrocatalysts have noteworthy advantages in maximizing the use of active sites. Among the pioneering works on such performing catalysts, the development of single-unit-cell-thick layered electrocatalysts (STLEs) has attracted extensive attention owing to their superior specific surface area and large number of vacancies, which can provide abundant available surface active sites. Therefore, this minireview provides recent advances in STLE synthesis and applications, which are helpful for electrocatalysis-oriented researchers. Finally, the future perspectives and challenges for developing high-performance STLEs are proposed.

Mixed Metal Phosphide Chainmail Catalysts Confined in N-Doped Porous Carbon Nanoboxes as Highly Efficient Water-Oxidation Electrocatalysts with Ultralow Overpotentials and Tafel Slopes

Electrocatalytic hydrogen production driven by surplus electric energies is considered a promising sustainable process for hydrogen supply. The high overpotential and low energy-conversion efficiency caused by the slow kinetics of the four-electron transfer oxygen-evolution reaction (OER), however, hamper its competitiveness. Herein, a highly stable, efficient OER catalyst was developed, taking the effects of both composition and nanostructure into account for the catalyst design. N-doped carbon-armored mixed metal phosphide nanoparticles confined in N-doped porous carbon nanoboxes, a particle-in-box nanostructure, were synthesized from monodisperse Ni₃[Fe(CN)₆]₂·H₂O nanocubes through sequential conformal polydopamine coating, ammonia etching, and thermal phosphorization. The product exhibited outstanding catalytic abilities for the OER in 1.0 M KOH, delivering 10, 100, and 250 mA/cm² at ultrasmall overpotentials of 203, 242, and 254 mV, respectively, with an ultrasmall Tafel slope of 38 mV/dec, outperforming most recently reported top-notch iron-group-based OER catalysts. The long-term stability was also excellent, showing a small chronopotentiometric decay of 2.5% over a 24 h operation at 50 mA/cm². The enhanced catalytic efficiency and stability may be attributable to the unique particle-in-box structure as a nanoreactor offering a local, fast reaction environment, the conductive N-doped porous carbon shell for fast charge and mass transport, the synergistic effect between multicomponent metal phosphides for enhanced intrinsic activities, and the carbon protection layer to prevent/delay the catalyst core from being deactivated. This combined particle-in-box and chainmail design concept for electrocatalysts is unique and advantageous and may be readily applied to the general field of heterogeneous reactions.

One-Step Synthesis of N, P-Codoped Carbon Nanosheets Encapsulated CoP Particles for Highly Efficient Oxygen Evolution Reaction

Oxygen electrocatalysis, especially oxygen evolution reaction (OER), is a central process during the actual application of rechargeable metal-air battery. It is still challenging to develop ideal electrocatalysts to substitute the commercial noble metal-based materials. In this work, we have constructed a new material, CoP nanoparticles, which are encapsulated by a biomolecule-derived N, P-codoped carbon nanosheets via a simple and facile one-step strategy. The as-prepared material releases a high electrocatalytic activity and stability for OER, with an overpotential of 310 mV to achieve 10 mA/cm2 in 1 M KOH. Importantly, we found that the phosphoric acid can not only introduce phosphorus dopant into 2D N-doped carbon nanosheets and play a role of pore-forming agent, but also participate in the formation of active center (cobalt phosphide). Moreover, the coverage of N, P-doped carbon can prevent the CoP nanoparticles from corrosion under the harsh reaction medium to achieve high and stable activity. We believe that our strategy can offer a novel pathway to synthesize new transition metal-based catalysts for electrocatalysis or other heterogeneous catalysis.

KB-templated in situ synthesis of highly dispersed bimetallic NiFe phosphides as efficient oxygen evolution catalysts

KB-templated in situ synthesized highly dispersed bimetallic NiFe phosphides function as efficient oxygen evolution catalysts.