Noble-Metal-Free Electrocatalysts for Oxygen Evolution

Electron-withdrawing anion intercalation and surface sulfurization of NiFe-layered double hydroxide nanoflowers enabling superior oxygen evolution performance

Unique NiFe-LDH nanoflowers functionalized with electron-withdrawing anion intercalation and surface sulfurization were fabricated, and show superior electrocatalytic activity for the oxygen evolution reaction.

Recent advances in ternary layered double hydroxide electrocatalysts for the oxygen evolution reaction

The recent advances in ternary layered double hydroxide electrocatalysts, including the strategies used for the design, synthesis, and evaluation of their performance for oxygen evolution reaction are reviewed in this account.

Noble metal-free two dimensional carbon-based electrocatalysts for water splitting

Noble metal materials are widely employed as benchmark electrocatalysts to achieve electrochemical water splitting which comprises of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, the high cost and scarcity limit the wide ranging commercial applications of noble metal-based catalysts. Development of noble metal-free two dimensional (2D) carbon-based materials can not only reduce the consumption of noble metals, but also create materials with the characteristics of high active surface area, abundance, easy functionalization, and chemical stability, which may carve a way to promising electrochemical water splitting. In this review, noble metal-free 2D carbon-based electrocatalysts, including heteroatom (B, S, N, P, F, and O) doped graphene, 2D porous carbons modified with heteroatoms and/or transition metals, and 2D carbon-based hybrids are introduced as cost-effective alternatives to the noble metal-based electrocatalysts with comparable efficiencies to conduct HER, OER, and overall water splitting. This review emphasizes on current development in synthetic strategies and structure–property relationships of noble metal-free 2D carbon-based electrocatalysts, together with major challenges and perspectives of noble metal-free 2D carbon-based electrocatalysts for further electrochemical applications.

Verchenko V, Shevelkov AV, Driess M. Boosting Water Oxidation through In Situ Electroconversion of Manganese Gallide: An Intermetallic Precursor Approach

For the first time, the manganese gallide (MnGa4 ) served as an intermetallic precursor, which upon in situ electroconversion in alkaline media produced high-performance and long-term-stable MnOx -based electrocatalysts for water oxidation. Unexpectedly, its electrocorrosion (with the concomitant loss of Ga) leads simultaneously to three crystalline types of MnOx minerals with distinct structures and induced defects: birnessite δ-MnO2 , feitknechtite β-MnOOH, and hausmannite α-Mn3 O4 . The abundance and intrinsic stabilization of MnIII /MnIV active sites in the three MnOx phases explains the superior efficiency and durability of the system for electrocatalytic water oxidation. After electrophoretic deposition of the MnGa4 precursor on conductive nickel foam (NF), a low overpotential of 291 mV, comparable to that of precious-metal-based catalysts, could be achieved at a current density of 10 mA cm-2 with a durability of more than five days.

NiFe Oxalate Nanomesh Array with Homogenous Doping of Fe for Electrocatalytic Water Oxidation

NiFe-based materials have shown impressive electrocatalytic activity for the oxygen evolution reaction (OER). The mutual effect between proximate Ni and Fe atoms is essential in regulating the electronic structure of the active site to boost the OER kinetics. Detailed studies confirm that the separated monometal phases in NiFe-based materials are detrimental to OER. Thus, the high-level blending of Ni and Fe in NiFe-based OER electrocatalysts is critical. Herein, an NiFe oxalate nanomesh array based on solid solutions between nickel (II) oxalate and iron (II) oxalate is prepared through a facile surfactant-free approach in the presence of the reductive oxalate anions. The integrated electrode can efficiently catalyze water oxidation to reach a current density of 50 mA cm^-2 with a small overpotential of 203 mV in a 1.0 m KOH aqueous solution. The high efficiency can be attributed to the atomic level mix of Ni and Fe in the solid solutions and the hierarchical porous structure of the nanomesh array. These two aspects bring about fast kinetics, efficient mass diffusion, and quick charge transfer, which are the three major positive factors for a high-performance heterogenous electrocatalyst.

Ultrafine Co3 O4 Nanoparticles within Nitrogen-Doped Carbon Matrix Derived from Metal-Organic Complex for Boosting Lithium Storage and Oxygen Evolution Reaction

Transition metal oxides have recently received great attention for application in advanced lithium-ion batteries (LIBs) and oxygen evolution reaction (OER). Herein, the ethylenediaminetetraacetic cobalt complex as a precursor to synthesize ultrafine Co₃ O₄ nanoparticles encapsulated into a nitrogen-doped carbon matrix (NC) composites is presented. The as-prepared Co₃ O₄ /NC-350 obtained by pyrolysis at 350 °C demonstrates superior rate performance (372 mAh g^-1 at 5.0 A g^-1 ) and high cycling stability (92% capacity retention after 300 cycles at 1.0 A g^-1 ) as anode for LIBs. When evaluated as an electrocatalyst for OER, the Co₃ O₄ /NC-350 achieves an overpotential of 298 mV at a current density of 10 mA cm^-2 . The NC-encapsualted porous hierarchical structure assures fast and continuous electron transportation, high activity sites, and strong structural integrity. This works offers novel complex precursors for synthesizing transition metal-based electrodes for boosting electrochemical energy conversion and storage.

Enhancing Oxygen Evolution Reaction through Modulating Electronic Structure of Trimetallic Electrocatalysts Derived from Metal-Organic Frameworks

The construction of efficient, durable, and non-noble metal electrocatalysts for oxygen evolution reaction (OER) is of great value but challenging. Herein, a facile method is developed to synthesize a series of trimetallic (W/Co/Fe) metal-organic frameworks (MOFs)-derived carbon nanoflakes (CNF) with various Fe content, and an Fe-dependent volcano-type plot can be drawn out for WCoFe_x -CNF. The optimized WCoFe_0.3 -CNF (when the feed ratio of Fe/Co is 0.3) demonstrates superior electrocatalytic performance with a low overpotential of only 254 mV@10 mA cm^-2 and excellent durability of 100 h. Further researches show that appropriate amount of iron doping can regulate the electronic structure, resulting in a favorable synergistic environment. This method may stimulate the exploration of electrocatalysts by utilizing MOFs as precursors while realizing electronic modulation by multimetal doping.

Inception of molybdate as a "pore forming additive" to enhance the bifunctional electrocatalytic activity of nickel and cobalt based mixed hydroxides for overall water splitting

Development of low-cost transition metal based electrocatalysts on inexpensive substrates for overall water splitting is essential to meet the future energy storage demand. In this article, we have synthesized a molybdate incorporated nickel cobalt hydroxide material on Cu mesh with nickel : cobalt : molybdenum in a 13.25 : 21.42 : 1 ratio and the electrode has shown excellent bifunctional electrocatalytic activity as it demonstrates overpotentials as low as 290 mV and 125 mV to reach 10 mA cm-2geo for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively (after both iR and capacitance correction). Control studies with fourteen other nickel-cobalt based hydroxides and rigorous post-catalytic analysis suggested that though molybdate was not the active catalytic centre, it played a pivotal role in enhancing the activity of the material as - (i) it significantly improved the surface area and porosity of the as-synthesized material and (ii) owing to its continuous etching during electrochemical testing, it was found to increase the accessibility of electrochemically active catalytic sites lying in the bulk. Thus, molybdate acts as a "pore forming additive" during both synthesis and electrochemical treatment. Furthermore, the combination of nickel and molybdate helped in the formation of a 2D-sheet like morphology which in turn improves accessibility to catalytically active centres. In addition, the Cu mesh substrate notably lowers the charge transfer resistance. To the best of our knowledge, this is the first ever report of molybdate as a "pore forming additive" and will enthuse the designing of electrocatalytic materials with enhanced performance based on this strategy.

Laser-Assisted Doping and Architecture Engineering of Fe3 O4 Nanoparticles for Highly Enhanced Oxygen Evolution Reaction

The design and synthesis of cost-effective and highperformance oxygen evolution reaction (OER) electrocatalysts for water splitting based on earth-abundant elements is urgent but challenging. A synergistic doping and architecture engineering strategy by nanosecond laser ablation is used to generate a unique kind of highly disordered Ni-doped Fe₃ O₄ nanoparticle clusters. Ni dopant and increased oxygen vacancies are simultaneously incorporated into Fe₃ O₄ frameworks and thereby modulate the electronic configuration for an optimal binding affinity towards OER intermediates. Nanoparticles with average size of around 5 nm assemble randomly during laser ablation and construct a fluffy and porous architecture, which not only optimizes the number of exposed active sites but also accelerates mass transfer. Consequently, Ni-doped Fe₃ O₄ clusters are revealed as a superior OER catalyst with a small overpotential of 272 mV at 10 mA cm^-2 and a small Tafel slope of 39.4 mV dec^-1 , surpassing almost all spinel Fe-based OER catalysts. This work provides a new strategy to fabricate advanced cation-doped metal oxide nanostructures for related energy applications.

Photocatalytic 4-nitrophenol degradation and oxygen evolution reaction in CuO/g-C3N4 composites prepared by deep eutectic solvent-assisted chlorine doping

Heterostructured Cl-CuO/g-C₃N₄ composite for OER and photocatalytic 4-nitrophenol degradation.

Preparation of hierarchical trimetallic coordination polymer film as efficient electrocatalyst for oxygen evolution reaction

A trimetallic coordination polymer film exhibits hierarchical structure with 1D interconnected nanofibers and can be an efficient OER electrocatalyst.

Metal-organic layer derived metal hydroxide nanosheets for highly efficient oxygen evolution

A series of metal hydroxide nanosheets have been fabricated from metal-organic layers (MOLs) through a conformal conversion process. Significantly, the MOL-derived Fe(OH)3 with an ultrathin layer structure exhibited enhanced alkaline oxygen evolution with a low overpotential of 271 mV at a current density of 10 mA cm-2.

Advanced electrospun nanomaterials for highly efficient electrocatalysis

We highlight the recent developments of electrospun nanomaterials with controlled morphology, composition and architecture for highly efficient electrocatalysis.

Noncovalent phosphorylation of CoCr layered double hydroxide nanosheets with improved electrocatalytic activity for the oxygen evolution reaction

Noncovalent phosphorylation of CoCr layered double hydroxide (LDH) was prepared by using P₂O₅ dissolved in isopropanol as a precursor, which showed improved catalytic activity for oxygen evolution reaction compared with pristine CoCr LDH.

Self-supported CoFe LDH/Co0.85Se nanosheet arrays as efficient electrocatalysts for the oxygen evolution reaction

Self-supported binary hybrid heterogeneous CoFe LDH/Co_0.85Se nanosheet array catalyst for efficient oxygen evolution reaction.

Humid atmospheric pressure plasma jets exposed micro-defects on CoMoO4 nanosheets with enhanced OER performance

A novel humid APPJs method was adopted to treat CoMoO₄ nanosheet arrays resulting in micro-defects and more reaction intermediates that led to an enhanced OER property.