MOF-based/derived catalysts for electrochemical overall water splitting

Phase Transition Engineering of Metal-Organic Frameworks Induces Multiphase Complexation for Enhancing the Oxygen Evolution Reaction

Phase transition engineering of metal-organic frameworks (MOFs) presents a promising strategy for enhancing electrocatalytic performance in water splitting applications. In this study, we demonstrate a controlled phase transition strategy to synthesize a multiphase composite (op&cp) composed of open phase (op) and closed phase (cp) through precise desolvation treatment. When used as an alkaline water electrocatalyst, op&cp exhibits exceptional oxygen evolution reaction (OER) performance, achieving a remarkably low overpotential of 140 mV under 10 mA cm-2 and maintaining stable operation for over 75 h at 100 mA cm-2. In situ Raman spectroscopy and X-ray photoelectron spectroscopy show that the catalytically active substance NiOOH is formed on the engineered phase with a lower potential (1.2 V vs RHE) than the single-phase material (1.3 V vs RHE). This work establishes phase transition engineering as a viable strategy for improving MOF-based catalysis and explores the fundamental mechanism of the dynamic evolution of active sites during the OER.

Electrochemical Hydrogen Evolution with Metal-Organic Framework-Derived Catalysts: Strategies for d-Band Modulation by Electronic Structure Modification

The effective use of metal-organic framework (MOF)-based materials in the electrocatalytic hydrogen evolution reaction (HER) relies on the understanding of their structural and electronic properties. While the structure and morphology of MOF-derived catalysts significantly impact HER activity, tuning the d-band structure through electronic structure modulation has emerged as a key factor in optimizing catalytic performance. Techniques such as composition tuning, heteroatom doping, surface modification, and interface engineering were found to be effective methods for manipulating the electronic configuration and, in turn, modulating the d-band. This review systematically explores the design strategies for MOF-derived catalysts by focusing on electronic structure modulation. It provides a detailed discussion of the various methods - used to modulate the electronic structure. Furthermore, the review establishes the relationship between d-band tuning, Gibbs free energy, and electronic structure modulation, supported by both spectroscopic and theoretical evidences.

Interface Engineering of Network-Like 1D/2D (NHCNT/Ni─MOF) Hybrid Nanoarchitecture for Electrocatalytic Water Splitting

Here, integrated functional components into a hybrid heterostructure via highly stabilized network-like interconnected electronic nanoarchitecture of 1D N-doped holey-carbon nanotube (NHCNT) with 2D nickel─metal-organic framework (Ni─MOF) nanosheets are developed as high-performance electrocatalyst for overall water splitting. The NHCNT promoting electron transport pathways in electrocatalyst, and formation of holes in nanotubes further enables excellent diffusion of ions for promoting the overall reaction rate. An excellent combination of 1D/2D structure of NHCNT/Ni─MOF-4 electrocatalyst exhibits excellent oxygen evolution reaction (η10 = 207.8 mV, and Tafel = 62.6 mV dec-1) and reasonable hydrogen evolution reaction (η10 = 159.8 mV, and Tafel = 107.69 mV dec-1) activity with consistent and stable performance in a 1 m KOH. The highly interconnected network structure contains Ni2+ and Ni3+ species in the NHCNT/Ni─MOF-4 electrocatalyst, which possesses high specific surface area (SSA) (235.53 m2 g-1), electrochemically active surface area (ECSA) (796.2 cm2), mass activity (4.76 mA mg-1), and turnover frequency (3.99 × 10-2 s-1), which provide remarkable electrocatalytic performance via generating synergy between the NHCNT and Ni─MOF. For overall water splitting, NHCNT/Ni─MOF-4 attains a low cell voltage (1.77 V@10 mA cm-2).

In-situ synthesis to promote surface reconstruction of metal-organic frameworks for high-performance water/seawater oxidation

Metal-organic frameworks (MOFs) have gained tremendous notice for the application in alkaline water/seawater oxidation due to their tunable structures and abundant accessible metal sites. However, exploring cost-effective oxygen evolution reaction (OER) electrocatalysts with high catalytic activity and excellent stability remains a great challenge. In this work, a promising strategy is proposed to regulate the crystalline structures and electronic properties of NiFe-metal-organic frameworks (NiFe-MOFs) by altering the organic ligands. As a representative sample, NiFe-BDC (BDC: C8H6O4) synthesized on nickel foam (NF) shows extraordinary OER activity in alkaline condition, delivering ultralow overpotentials of 204, 234 and 273 mV at 10, 100, and 300 mA cm-2, respectively, with a small Tafel slope of 21.6 mV dec-1. Only a slight decrease is observed when operating in alkaline seawater. The potential attenuation is barely identified at 200 mA cm-2 over 200 h continuous test, indicating the remarkable stability and corrosion resistance. In-situ measurements indicate that initial Ni2+/Fe2+ goes through oxidation process into Ni3+/Fe3+ during OER, and eventually presents in the form of NiFeOOH/NiFe-BDC heterojunction. The unique self-reconstructed surface is responsible for the low reaction barrier and fast reaction kinetics. This work provides an effective strategy to develop efficient MOF-based electrocatalysts and an insightful view on the dynamic structural evolution during OER.

Syntheses of heterometallic organic frameworks catalysts via multicomponent postmodification: For improving CO2 photoreduction efficiency

To enhance the economic viability of photocatalytic materials for carbon capture and conversion, the challenge of employing expensive photosensitizer must be overcome. This study aims to improve the visible light utilization with zirconium-based metal-organic frameworks (Zr-MOFs) by employing a multi-component post-synthetic modification (PSM) strategy. An economical photosensitiser and copper ions are introduced into MOF 808 to enhance its photoreduction properties. Notably, the PSM of MOF 808 shows the highest CO yield up to 236.5 μmol g-1 h-1 with aHCOOH production of 993.6 μmol g-1 h-1 under non-noble metal, and its mechanistic insight for CO2 reaction is discussed in detail. The research results have important reference value for the potential application of photocatalytic metal-organic frameworks.

Efficient Adsorption and Degradation of Tetracycline Hydrochloride Using Metal-Organic Framework-Derived Cobalt-Based Catalysts and Mechanism Insight

High-performance Co-based catalysts were derived by pyrolysis using synthesized MOFs as self-sacrificial templates. Various catalytic systems were constructed by peroxymonosulfate (PMS) to degrade tetracycline hydrochloride (TC). Adsorption-degradation efficiencies, cycle performance, dynamics, and the adsorption catalytic mechanism of various catalytic systems for TC were studied. The effects of different synthetic solvents, pyrolysis temperatures, and single/bimetallic element compositions on degradation efficiency were innovatively compared. The optimal catalyst and PMS dosage for the experiment were determined to be 10 mg and 0.1 mL, respectively. The results indicated that all catalytic systems could efficiently degrade TC and have a high acid-base resistance. The catalyst activity was significantly influenced by the pyrolysis temperature. The optimum pyrolysis temperatures for Zn@Co-N-C-T, CH3OH@Co-N-C-T, and H2O@Co-N-C-T were 1000, 900 and 900 °C, respectively. More abundant pore structures and active sites were generated in Zn@Co-N-C-1000, exhibiting an excellent TC degradation efficiency and adsorption capacity, achieving 94.73% and 167.564 mg/g, respectively. Meanwhile, the total organic carbon (TOC) of TC (50 mL, 50 mg/L) achieved a removal rate (TOC/TOC0) of 50.28%. Zn@Co-N-C-1000/PMS maintained over 83.27% TC degradation after five cycles. The adsorption mechanism of the catalyst for TC was investigated through the analysis of adsorption kinetics and isotherm models. The quenching test and EPR results indicated that TC was primarily degraded through the nonradical pathway. The efficient degradation of TC is attributed to the rapid electron transfer processes occurring at the two-phase interface and the redox cycling of Co0/Co2+/Co3+. Finally, LC-MS was used to analyze the intermediate products of TC degradation in the Zn@Co-N-C-1000/PMS system, and two degradation pathways were proposed.

Manipulating heterointerface to boost formation and desorption of intermediates for highly efficient alkaline hydrogen evolution

Promoting water dissociation and H intermediate desorption play a pivotal role in achieving highly efficient hydrogen evolution reaction (HER) in alkaline media but remain a great challenge. Herein, we rationally develop a unique W-doped NiSx/Ni heterointerface as a favorable HER electrocatalyst which was directly grown on the Cu nanowire foam substrate (W-NiSx/Ni@Cu) by the electrodeposition strategy. Benefiting from the rational design of the interfaces, the electronic coupling of the W-NiSx/Ni@Cu can be efficiently modulated to lower the HER kinetic barrier. The obtained W-NiSx/Ni@Cu exhibits an enhanced HER activity with a low overpotential of 38 mV at 10 mA cm-2 and a small Tafel value of 27.5 mV dec-1, and high stability during HER catalysis. In addition, in-situ Raman spectra reveal that the Ni2+ active sites preferentially adsorb OH intermediate. The theoretical calculation confirms that the water dissociation is accelerated by the construction of W-NiSx/Ni heterointerface and H intermediate desorption can be also promoted by H spillover from S active sites in W-NiSx to Ni active sites in metal Ni. This work offers a valuable reference for rational designing heterointerface of electrocatalysts and provides an available method to accelerate the HER kinetics for the ampere-level current density under low overpotential.

Rare earth elements induced electronic engineering in Rh cluster toward efficient alkaline hydrogen evolution reaction

The unique electronic and crystal structures of rare earth metals (RE) offer promising opportunities for enhancing the hydrogen evolution reaction (HER) properties of materials. In this work, a series of RE (Sm, Nd, Pr and Ho)-doped Rh@NSPC (NSPC stands for N, S co-doped porous carbon nanosheets) with sizes less than 2 nm are prepared, utilizing a simple, rapid and solvent-free joule-heat pyrolysis method for the first time. The optimized Sm-Rh@NSPC achieves HER performance. The high-catalytic performance and stability of Sm-Rh@NSPC are attributed to the synergistic electronic interactions between Sm and Rh clusters, leading to an increase in the electron cloud density of Rh, which promotes the adsorption of H+, the dissociation of Rh-H bonds and the release of H2. Notably, the overpotential of the Sm-Rh@NSPC catalyst is a mere 18.1 mV at current density of 10 mAcm-2, with a Tafel slope of only 15.2 mV dec-1. Furthermore, it exhibits stable operation in a 1.0 M KOH electrolyte at 10 mA cm-2 for more than 100 h. This study provides new insights into the synthesis of composite RE hybrid cluster nanocatalysts and their RE-enhanced electrocatalytic performance. It also introduces fresh perspectives for the development of efficient electrocatalysts.