In situ assembly of metal-organic framework-derived N-doped carbon/Co/CoP catalysts on carbon paper for water splitting in alkaline electrolytes

MOF-based/derived catalysts for electrochemical overall water splitting

Water-splitting electrocatalysis has gained increasing attention as a promising strategy for developing renewable energy in recent years, but its high overpotential caused by the unfavorable thermodynamics has limited its widespread implementation. Therefore, there is an urgent need to design catalytic materials with outstanding activity and stability that can overcome the high overpotential and thus improve the electrocatalytic efficiency. Metal-organic frameworks (MOFs) based and/or derived materials are widely used as water-splitting catalysts because of their easily controlled structures, abundant heterointerfaces and increased specific surface area. Herein, some recent research findings on MOFs-based/derived materials are summarized and presented. First, the mechanism and evaluation parameters of electrochemical water splitting are described. Subsequently, advanced modulation strategies for designing MOFs-based/derived catalysts and their catalytic performance toward water splitting are summarized. In particular, the correlation between chemical composition/structural functionalization and catalytic performance is highlighted. Finally, the future outlook and challenges for MOFs materials are also addressed.

One-Step Electrodeposition of a Mesoporous Ni/Co-Imidazole-Based Bimetal-Organic Framework on Pyramid-like NiSb with Abundant Coupling Interfaces as an Ultra-Stable Heterostructural Electrocatalyst for Water Splitting

The exploration of highly efficient metal-organic framework (MOF)-based electrocatalysts is a research topic of high significance owing to their potential applications in sustainable and clean energy production. Herein, a mesoporous MOF containing Ni and Co nodes along with 2-methylimidazole (Hmim) ligands has been directly grown on the surface of the pyramid-like NiSb through a convenient cathodic electrodeposition strategy and evaluated as the catalyst for water splitting catalysis. Tailoring catalytically active sites through porous well-arranging architecture and the coupled interface offers a catalyst with exquisite performance that displays ultra-low Tafel constant of 33 and 42 mV dec^-1 toward the hydrogen evolution reaction and oxygen evolution reaction, sequentially, and also enhanced durability at high current densities over 150 h in a 1 M KOH medium. The success of the synthesized NiCo-MOF@NiSb@GB electrode is explained by the intimate contact between the NiCo-MOF and NiSb with well-tailored phase interfaces, the positive coupling effect between Ni and Co metal centers in the MOF, and the porous structure with abundant active sites toward electrocatalysis. Importantly, the present work provides a new technical reference for the electrochemical synthesis of heterostructural MOFs as a promising candidate for energy-related applications.

Defect engineering and atomic doping of porous Co-Ni2P nanosheet arrays for boosting electrocatalytic oxygen evolution

Electrochemical hydrogen production by splitting water is mainly limited to the oxygen evolution reaction (OER), which requires high energy consumption. The design of an efficient and stable electrochemical catalyst is the key to solving this problem. Here, a three-dimensional porous Co-doped Ni₂P nanosheet (Co-Ni₂P/NF-corr) was synthesized by simple hydrothermal, acid leaching and phosphating processes successively. Excitingly, the current density of Co-Ni₂P-corr in 1 M KOH solution can reach 50 mA cm^-2 with only 267 mV overpotential. Moreover, the Tafel slope is very small, only 64 mV dec^-1. In addition, the stability test shows that it can work stably at 50 mA cm^-2 current density for at least 48 h.

Construction of Petal-Like Ag NWs@NiCoP with Three-Dimensional Core-Shell Structure for Overall Water Splitting

High-efficiency, good electrical conductivity and excellent performance electrocatalysts are attracting growing attention in the field of overall water splitting. In order to achieve the desirable qualities, rational construction of the structure and chemical composition of electrocatalysts is of fundamental importance. Herein, petal-like structure Ni0.33Co0.67P shells grown on conductive silver nanowires (Ag NWs) cores as bifunctional electrocatalysts for overall water splitting were synthesized through a facile hydrothermal method and phosphorization. The resultant three-dimensional core-shell petal-like structure Ag NWs@Ni0.33Co0.67P possesses excellent catalytic activities in alkaline conditions with the overpotential of 259 mV for the oxygen evolution reaction (OER), 121 mV for the hydrogen evolution reaction (HER) and a full cell voltage of 1.64 V to reach the current density of 10 mA cm-2. Highly conductive Ag NWs as cores and high surface area petal-like Ni0.33Co0.67P as shells can endow outstanding catalytic performance for the bifunctional electrocatalyst. Thus, the synthetic strategy of the three-dimensional core-shell structure Ag NWs@Ni0.33Co0.67P considerably advances the practice of Ag NWs toward electrocatalysts.

N, P-doped carbon supported ruthenium doped Rhenium phosphide with porous nanostructure for hydrogen evolution reaction using sustainable energies

Developing efficient and cost-effective catalysts for hydrogen evolution reaction (HER) is vital to hydrogen energy's commercial applications. In this study, N,P-doped carbon supported ruthenium (Ru) doped triruthenium tetraphosphide (Re₃P₄) (Ru-Re₃P₄/NPC) with porous nanostructure is prepared using the low-toxic melamine phosphate as the carbon and phosphorous source. The in-situ generated N,P-doped carbon layers play a pivotal role in regulating the electrocatalytic activity by avoiding the aggregation of the nanoparticles and increasing the specific surface area. Moreover, Ru doping contributes to the remarkable electrocatalytic performance of the prepared nanomaterials. Impressively, the as-synthesized Ru-Re₃P₄/NPC presents remarkable electrocatalytic performances toward HER with small overpotentials of 39 mV, 115 mV, and 88 mV to deliver 10 mA cm^-2 in alkaline, neutral, and acidic media. Moreover, the prepared electrocatalyst can drive water-splitting with a small potential of 1.45 V@10 mA cm^-2 and use sustainable energies, including solar, wind, and thermal, as electric resources. This work paves a novel and valuable way to enhance the electrocatalytic performances of metal phosphides.

3D nanoporous NiCoP as a highly efficient electrocatalyst for the hydrogen evolution reaction in alkaline electrolyte

3D nanoporous NiCoP properly inherits the dealloyed double-continuous nanoporous structure, enables fast charge transfer, and fully reflects its inherent activity.

Facile Synthesis of MoP-RuP2 with Abundant Interfaces to Boost Hydrogen Evolution Reactions in Alkaline Media

Exploiting efficient electrocatalysts for hydrogen evolution reactions (HERs) is important for boosting the large-scale applications of hydrogen energy. Herein, MoP-RuP₂ encapsulated in N,P-codoped carbon (MoP-RuP₂@NPC) with abundant interfaces were prepared via a facile avenue with the low-toxic melamine phosphate as the phosphorous resource. Moreover, the obtained electrocatalyst possessed a porous nanostructure, had abundant exposed active sites and improved the mass transport during the electrocatalytic process. Due to the above merits, the prepared MoP-RuP₂@NPC delivered a greater electrocatalytic performance for HERs (50 mV@10 mA cm⁻²) relative to RuP₂@NPC (120 mV) and MoP@NPC (195 mV) in 1 M KOH. Moreover, an ultralow potential of 1.6 V was required to deliver a current density of 10 mA cm⁻² in the two-electrode configuration for overall water splitting. For practical applications, intermittent solar energy, wind energy and thermal energy were utilized to drive the electrolyzer to generate hydrogen gas. This work provides a novel and facile strategy for designing highly efficient and stable nanomaterials toward hydrogen production.

A Janus cobalt nanoparticles and molybdenum carbide decorated N-doped carbon for high-performance overall water splitting

The fabrication of high-performance and stable electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of importance for sustainable water-splitting technologies. Herein, the cobalt (Co) nanoparticles and molybdenum carbide (Mo₂C) heterostructures anchored N-doped carbon (Co/Mo₂C@NC-800) was designed as bifunctional electrocatalyst for overall water splitting via a simple pyrolysis approach for metal organic frameworks (MOFs) precursor. This composite shows a remarkable performance for HER and OER with a small overpotential of 121 mV and 311 mV at 10 mA cm^-2, respectively. When the optimized electrocatalyst was employed as both anode and cathode for overall water splitting in a two-electrode system, the electrolyzer achieves a low cell voltage of 1.67 V at 10 mA cm^-2 in 1 M KOH, as well as a superior and stable long-time operation of 30 h. The promising hybrid material demonstrates excellent electrocatalysis performance due to effective combination of the best of both worlds: Mo₂C with remarkable HER performance and Co nanoparticles with excellent OER activity. The Mo₂C possesses strong hydrogen binding energy and Co exhibits prominent electrical conductivity, thus the construction of heterostructures achieves more active sites with different functions and significantly boosts HER and OER process. The novel and effective synthesis strategy provides new insights into the design of outstanding non-noble metal bifunctional electrocatalysts for overall water splitting.

Targeted Assembly of Ultrathin NiO/MoS2 Electrodes for Electrocatalytic Hydrogen Evolution in Alkaline Electrolyte

The development of non-noble metal catalysts for hydrogen revolution in alkaline media is highly desirable, but remains a great challenge. Herein, synergetic ultrathin NiO/MoS₂ catalysts were prepared to improve the sluggish water dissociation step for HER in alkaline conditions. With traditional electrode assembly methods, MoS₂:NiO-3:1 exhibited the best catalytic performance; an overpotential of 158 mV was required to achieve a current density of 10 mA/cm². Further, a synergetic ultrathin NiO/MoS₂/nickel foam (NF) electrode was assembled by electrophoretic deposition (EPD) and post-processing reactions. The electrode displayed higher electrocatalytic ability and stability, and an overpotential of only 121 mV was needed to achieve a current density of 10 mA/cm². The improvement was ascribed to the better catalytic environment, rather than a larger active surface area, a higher density of exposed active sites or other factors. DFT calculations indicated that the hybrid NiO/MoS₂ heterostuctured interface is advantageous for the enhanced water dissociation step and the corresponding lower kinetic energy barrier—from 1.53 to 0.81 eV.

Zirconium doping level modulation combined with chalconylthiourea organic frameworks induced enhancement of luminescence applied to cell imaging

Derivatives of a zirconium metal–organic framework as the center polymer material with a chalconylthiourea polymer (CT) were applied to cell imaging.