Fe-doping effect on CoTe catalyst with greatly boosted intrinsic activity for electrochemical oxygen evolution reaction

Recent Progress on Nickel- and Iron-Based Metallic Organic Frameworks for Oxygen Evolution Reaction: A Review

Developing sustainable energy solutions to safeguard the environment is a critical ongoing demand. Electrochemical water splitting (EWS) is a green approach to create effective and long-lasting electrocatalysts for the water oxidation process. Metal organic frameworks (MOFs) have become commonly utilized materials in recent years because of their distinguishing pore architectures, metal nodes easy accessibility, large specific surface areas, shape, and adaptable function. This review outlines the most significant developments in current work on developing improved MOFs for enhancing EWS. The benefits and drawbacks of MOFs are first discussed in this review. Then, some cutting-edge methods for successfully modifying MOFs are also highlighted. Recent progress on nickel (Ni) and iron (Fe) based MOFs have been critically discussed. Finally, a comprehensive analysis of the existing challenges and prospects for Ni- and Fe-based MOFs are summarized.

A Review of Transition Metal Boride, Carbide, Pnictide, and Chalcogenide Water Oxidation Electrocatalysts

Transition metal borides, carbides, pnictides, and chalcogenides (X-ides) have emerged as a class of materials for the oxygen evolution reaction (OER). Because of their high earth abundance, electrical conductivity, and OER performance, these electrocatalysts have the potential to enable the practical application of green energy conversion and storage. Under OER potentials, X-ide electrocatalysts demonstrate various degrees of oxidation resistance due to their differences in chemical composition, crystal structure, and morphology. Depending on their resistance to oxidation, these catalysts will fall into one of three post-OER electrocatalyst categories: fully oxidized oxide/(oxy)hydroxide material, partially oxidized core@shell structure, and unoxidized material. In the past ten years (from 2013 to 2022), over 890 peer-reviewed research papers have focused on X-ide OER electrocatalysts. Previous review papers have provided limited conclusions and have omitted the significance of "catalytically active sites/species/phases" in X-ide OER electrocatalysts. In this review, a comprehensive summary of (i) experimental parameters (e.g., substrates, electrocatalyst loading amounts, geometric overpotentials, Tafel slopes, etc.) and (ii) electrochemical stability tests and post-analyses in X-ide OER electrocatalyst publications from 2013 to 2022 is provided. Both mono and polyanion X-ides are discussed and classified with respect to their material transformation during the OER. Special analytical techniques employed to study X-ide reconstruction are also evaluated. Additionally, future challenges and questions yet to be answered are provided in each section. This review aims to provide researchers with a toolkit to approach X-ide OER electrocatalyst research and to showcase necessary avenues for future investigation.

Oxygen-Plasma-Induced Hetero-Interface NiFe2O4/NiMoO4 Catalyst for Enhanced Electrochemical Oxygen Evolution

The electrolysis of water to produce hydrogen is an effective method for solving the rapid consumption of fossil fuel resources and the problem of global warming. The key to its success is to design an oxygen evolution reaction (OER) electrocatalyst with efficient conversion and reliable stability. Interface engineering is one of the most effective approaches for adjusting local electronic configurations. Adding other metal elements is also an effective way to enrich active sites and improve catalytic activity. Herein, high-valence iron in a heterogeneous interface of NiFe2O4/NiMoO4 composite was obtained through oxygen plasma to achieve excellent electrocatalytic activity and stability. In particular, 270 mV of overpotential is required to reach a current density of 50 mA cm-2, and the overpotential required to reach 500 mA cm-2 is only 309 mV. The electron transfer effect for high-valence iron was determined by X-ray photoelectron spectroscopy (XPS). The fast and irreversible reconstruction and the true active species in the catalytic process were identified by in situ Raman, ex situ XPS, and ex situ transmission electron microscopy (TEM) measurements. This work provides a feasible design guideline to modify electronic structures, promote a metal to an active oxidation state, and thus develop an electrocatalyst with enhanced OER performance.

Critical Review, Recent Updates on Zeolitic Imidazolate Framework-67 (ZIF-67) and Its Derivatives for Electrochemical Water Splitting

Design and construction of low-cost electrocatalysts with high catalytic activity and long-term stability is a challenging task in the field of catalysis. Metal-organic frameworks (MOF) are promising candidates as precursor materials in the development of highly efficient electrocatalysts for energy conversion and storage applications. This review starts with a summary of basic concepts and key evaluation parameters involved in the electrochemical water-splitting reaction. Then, different synthesis approaches reported for the cobalt-based Zeolitic imidazolate framework (ZIF-67) and its derivatives are critically reviewed. Additionally, several strategies employed to enhance the electrocatalytic activity and stability of ZIF-67-based electrocatalysts are discussed in detail. The present review provides a succinct insight into the ZIF-67 and its derivatives (oxides, hydroxides, sulfides, selenides, phosphide, nitrides, telluride, heteroatom/metal-doped carbon, noble metal-supported ZIF-67 derivatives) reported for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting applications. Finally, this review concludes with the associated challenges and the perspectives on developing the best economic, durable electrocatalytic materials.

Porous FeP/CoP heterogeneous materials as efficient alkaline oxygen evolution reaction (OER) catalysts

Transition metal phosphides have been widely studied because of their low cost and good conductivity, attempting to replace precious metal-based materials as new electrochemical catalysts for oxygen evolution reaction.

Enhancing Effect of Fe2+ Doping of Ni/NiO Nanocomposite Films on Catalytic Hydrogen Generation

Highly active and stable non-noble metal catalysts are expected to play a critical role in future hydrogen storage and conversion applications. The design of active sites with composite oxides provides a new approach for developing high-performance catalysts. In this study, an Fe-doped Ni/NiO nanocomposite film was constructed on an ionic liquid/water interface to promote hydrogen generation. The optimized Ni/FeNiO_x-25 catalyst showed excellent catalytic activity toward ammonia borane hydrolysis, with a turnover frequency of 72.3 min^-1. The enhancing effect of Fe²⁺ doping on Ni/NiO films was confirmed by the improved intrinsic activity and theoretical simulations. Fe ion doping stabilized NiO and prevented NiO from becoming Ni. The interfacial Ni-Fe²⁺ dual active sites on the FeNiO_x and Ni interfaces participated in the targeted adsorption and effective activation of water and NH₃BH₃ molecules, respectively. The sufficiently exposed plane surface of the nanofilms provided abundant active sites for catalytic reactions. This significant advance will inspire development in the ambient liquid hydrogen storage field.

Hollow Pd/Te nanorods for the effective electrooxidation of methanol

Methanol electrooxidation is significant in realizing effective C1 liquid fuel applications. Herein, hollow Pd/Te nanorods were fabricated and evaluated for methanol oxidation, and they were found to exhibit high catalytic efficiency for methanol oxidation in alkaline electrolyte compared to Pd or Pd/C catalysts. The hybrid structure of hexagonal crystal Te and face-centered cubic Pd was formed by microwave assisted Pd nanoparticle deposition over the surface of Te nanorods. Strong electronic effects and facile oxophilic properties were indicated in the Pd/Te system by spectroscopic analysis, which mainly accounts for the high catalytic performance for methanol oxidation. Specifically, they showed a peak current density of 90.1 mA cm^-2 for methanol oxidation, around 3.5 times higher than that of commercial Pd/C (26.3 mA cm^-2). High catalytic stability was also observed for Pd/Te, with a current retention of 64.3% after 3600 s of chronoamperometric testing, much higher than for Pd catalysts (20.1%). High anti-CO poisoning ability of the Pd/Te catalyst was demonstrated in the CO-stripping voltammetry results, and faster catalytic kinetics were also observed for this catalyst system. The electron-rich state of Pd and high active site exposure are responsible for the high performance of the Pd/Te catalyst in methanol oxidation.

The importance of the iron valence state in NiCoFe nanosheet array catalysts for the oxygen evolution reaction

The catalytic performances of NiCoFe nanosheet array catalysts for the OER are strongly dependent on the valence state of iron cations in the precursors.

Pt-Co3O4 Superstructures by One-Pot Reduction/Precipitation in Bicontinuous Microemulsion for Electrocatalytic Oxygen Evolution Reaction

Bicontinuous microemulsions (BCME) were used to synthesize hierarchical superstructures (HSs) of Pt-Co3O4 by reduction/precipitation. BCMEs possess water and oil nanochannels, and therefore, both hydrophilic and lipophilic precursors can be used. Thus, PtAq-CoAq, PtAq-CoOi, PtOi-CoAq and PtOi-CoOi were prepared (where Aq and Oi stand for the precursor present in aqueous or oily phase, respectively). The characterization of the Pt-Co3O4-HS confirmed the formation of metallic Pt and Co3O4 whose composition and morphology are controlled by the initial pH and precursor combination, determining the presence of the reducing/precipitant species in the reaction media. The electrocatalytic activity of the Pt-Co3O4-HSs for oxygen evolution reaction (OER) was investigated using linear sweep voltammetry in 0.1 M KOH and compared with Pt-HS. The lowest onset overpotentials for Pt-Co3O4-Hs were achieved with PtOi-CoOi (1.46 V vs. RHE), while the lowest overpotential at a current density of 10 mA cm−2 (η10) was obtained for the PtAq-CoAq (381 mV). Tafel slopes were 102, 89, 157 and 92 mV dec−1, for PtAq-CoAq, PtAq-CoOi, PtOi-CoAq and PtOi-CoOi, respectively. The Pt-Co3O4-HSs showed a better performance than Pt-HS. Our work shows that the properties and performance of metal–metal oxide HSs obtained in BCMEs depend on the phases in which the precursors are present.

Phosphorus-doped CoTe2/C nanoparticles create new Co-P active sites to promote the hydrogen evolution reaction

Doping has been widely recognized as an effective method for adjusting the performance of electrocatalysts. It can cause changes in the electronic structure of substances. Thereby, it can affect the intrinsic catalytic performance. Herein, we report a facile doping method in which phosphorus can be simultaneously doped into both CoTe2 and C. In the acidic solution, the hydrogen evolution reaction (HER) performance of the obtained P-CoTe2/C nanoparticles was significantly improved compared with that of undoped nanoparticles. At a current density of 10 mA cm-2, the overpotential decreased from 430 mV to 159 mV. Density functional theory (DFT) calculations show that phosphorus doping can produce new high activity Co-P catalytic sites. In addition, phosphorus can be doped into the carbon in the composite at the same time, which enhances the electrical conductivity of the composite. Moreover, in the process of calcination and doping, the electric double layer capacitance (Cdl) of the composite is significantly increased, which helps in exposing more active sites. This work has developed a multi-effect doping method that simultaneously increases the intrinsic activity, conductivity and active sites of the material. This method provides a new strategy for the performance regulation of other electrocatalysts.

One-step fabrication of a self-supported Co@CoTe2 electrocatalyst for efficient and durable oxygen evolution reactions

The optimal hydrothermal synthesis of a Co@CoTe₂-240 electrode needs an overpotential of 286 mV to achieve a current density of 10 mA cm⁻² and is able to sustain galvanostatic OER electrolysis for 16 hours with little degradation of less than 20 mV.