Electrocatalytic Oxygen Evolution Reaction Research Articles

RuO2 Catalysts for Electrocatalytic Oxygen Evolution in Acidic Media: Mechanism, Activity Promotion Strategy and Research Progress.

Proton Exchange Membrane Water Electrolysis (PEMWE) under acidic conditions outperforms alkaline water electrolysis in terms of less resistance loss, higher current density, and higher produced hydrogen purity, which make it more economical in long-term applications. However, the efficiency of PEMWE is severely limited by the slow kinetics of anodic oxygen evolution reaction (OER), poor catalyst stability, and high cost. Therefore, researchers in the past decade have made great efforts to explore cheap, efficient, and stable electrode materials. Among them, the RuO2 electrocatalyst has been proved to be a major promising alternative to Ir-based catalysts and the most promising OER catalyst owing to its excellent electrocatalytic activity and high pH adaptability. In this review, we elaborate two reaction mechanisms of OER (lattice oxygen mechanism and adsorbate evolution mechanism), comprehensively summarize and discuss the recently reported RuO2-based OER electrocatalysts under acidic conditions, and propose many advanced modification strategies to further improve the activity and stability of RuO2-based electrocatalytic OER. Finally, we provide suggestions for overcoming the challenges faced by RuO2 electrocatalysts in practical applications and make prospects for future research. This review provides perspectives and guidance for the rational design of highly active and stable acidic OER electrocatalysts based on PEMWE.

Surface reconstruction of La0.6Sr0.4Co0.8Ni0.2O3-δ perovskite nanofibers for oxygen evolution reaction

Perovskites have become promising alternatives to precious metal-catalyzed oxygen evolution reaction (OER). Herein, we report the synthesis of several perovskite nanofibers, specifically La0.6Sr0.4CoxNi1-xO3-δ (LSCN), and investigate their electrocatalytic water oxidation activity in alkaline electrolytes. La0.6Sr0.4Co0.8Ni0.2O3-δ (LSCN-0.8) is selected and immersed in an aqueous NaBH4 solution for 1 h for surface reconstruction. The perovskite nanofibers' electrocatalytic OER activity and stability are rigorously evaluated using a standard three-electrode system. Results reveal that even a slight Co substitution for Ni content within the LSCN perovskite structure has a notable impact on electrocatalytic activity. Moreover, LSCN-0.8 exhibits an overpotential of 363 mV at 20 mA cm−2 in 1 M KOH. However, significant improvement is observed after the surface reconstruction process. The optimized LSCN-0.8 (now called LSCN-2) displays the lowest OER overpotential (320 mV) under the same conditions. Furthermore, the LSCN-2 nanostructure demonstrates exceptional electrode stability, as evidenced by only a slight decrease in electrocatalytic performance during 5000 cycles of linear sweep voltammetry.

Interatomic interaction of 2D crumpled V2O5 nanosheets layered with Ni-MOF as a bifunctional electrocatalyst for overall water splitting and supercapacitor applications

Herein, we have synthesized a highly efficient and economical noble metal-free catalyst via a novel combination of V2O5 nanosheets and Ni MOF. The critical points of this study are (i) achieving a 2D layer structured crumpled V2O5 nanosheets without excessive stacking/aggregation using freeze drying method, (ii) decorating Ni-MOF over the crumpled V2O5 nanosheets to attain an excellent homogeneity and (iii) developing a V2O5 based novel and bifunctional electrocatalyst for overall water splitting and supercapacitor applications. Forming a well-interlinked morphological structure accompanies a homogeneous dispersion of Ni MOF over the V2O5 nanosheet. Among the multiple compositions, the NiV4 exhibited superior electrocatalytic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performances with an overpotential (η30) of 336 mV and 108 mV, respectively. NiV4 also displayed remarkable stability as confirmed by chronopotentiometry (24 h) and CV (after 5000 cycles). The excellent OER performance is possible due to the interatomic interaction and the heterojunction formation between V2O5 nanosheets and Ni MOF, resulting in the preferential adsorption of ⁎OOH reaction intermediates to Ni active sites. During HER, the interfacial interaction between V2O5 nanosheets and Ni MOF allowed the OH− to adsorb on the V5+ center. Furthermore, the Ni active sites simultaneously accelerated the Volmer step by promoting the H adsorption. The uniform mass transfer routes aid in fast charge transfer, resulting in excellent OER and HER performances. Interestingly, in the 2-electrode system, the NiV4 exhibited an overpotential of 1.81 V at 10 mA cm−2 and excellent durability over 15 h. For supercapacitor applications, the NiV4 exhibits efficient specific capacitance (546 Fg−1 at 1Ag−1). Furthermore, the NiV4 electrode provides significant long-term stability during the supercapacitor application, with the stability being consistent after 10,000 cycles. The NiV4 offers excellent water splitting and supercapacitor performance due to its multifunctional properties and remarkable structural integrity.

Polypyrrole-wrapped Hofmann type metal–organic framework nanoflowers to boost oxygen evolution reaction

The exploration of efficient and stable metal-organic frameworks (MOFs) for electrocatalytic oxygen evolution reaction (OER) has received increasing attention. However, the limited electronic conductivity of MOFs hinders the electron transfer rate. Herein, we report the preparation of conducting polypyrrole (PPy)-modified MOF nanoflowers (MOF-NFs@PPy) as promising electrocatalysts for OER. The PPy layer significantly increases the electrical conductivity and modulates the ionic transmittance between MOF-NFs and the electrolyte. The interaction of PPy with the MOF-NFs modifies the electronic structure and improves the reaction efficiency at the active sites. The obtained MOF-NFs@PPy exhibits excellent electrocatalytic activity with an OER overpotential of only 218 mV@10 mA cm−2 and small Tafel slope of 47.4 mV dec−1. In addition, the MOF-NFs@PPy exhibited excellent long-term stability (>24 h). This work may provide a new idea and a novel construction strategy for MOFs to improve OER performance.

Highly Porous Carbon Flakes Derived from Cellulose and Nickel Phosphide Heterostructure towards Efficient Electrocatalysis of Oxygen Evolution Reaction.

This study delves into the pressing challenges of climate change and the escalating carbon dioxide (CO2) emissions by exploring hydrogen technology as a sustainable alternative. In particular, there is focus on nickel phosphide-based electrocatalysts, known for their promising performance in hydrogen evolution reactions (HERs) and oxygen evolution reactions (OERs). Therefore, here we have designed a facile strategy to deliver highly porous carbon flakes derived from cellulose fibers via carbonization at 850 °C, yielding highly porous structures and outstanding specific surface area (SSAcel_carb_850_act = 3164 m2/g) after activation. As-fabricated carbon was utilized as a support for Ni12P5 with an optimized mass ratio. Electrochemical testing revealed that the composite of Ni12P5 and carbon flakes with a ratio of 100:1, respectively, exhibited the most favorable kinetics for the oxygen evolution reaction (OER). Importantly, the durability tests of this sample demonstrated the most stable behavior and lowest potential change under high current density among the studied samples, making it a promising candidate in practical applications. Moreover, the analysis of electrocatalysts after an OER does not show any changes, indicating that the sample does not undergo undesired intermediate reactions and that unwanted products are not released, explaining its stable behavior. This provides a straightforward approach for creating a cellulose-derived composite with enhanced electroactivity and durability.

Construction of Ni2P@NiCo-BLDH nanocomposite with hierarchical porous structure on nickel foam as advanced oxygen evolution electrocatalyst

The fabrication of two-dimensional layered double hydroxides (LDHs) materials still faces great challenges, particularly in achieving precise modulation of lamellar metals and interlayer anions for electrocatalytic oxygen evolution reaction (OER). Herein, a hierarchical porous nanocomposite assembled by foam nickel (NF) supported borate anions incorporated bimetallic NiCo hydrotalcite (NiCo-BLDH) on the surface of nickel phosphide sheets (NF/Ni2P @ NiCo-BLDH) is prepared through the NF in-situ phosphating and electrodeposition approach as an electrocatalyst for achieving superior OER catalysis. In this design, introducing multi-phase and incorporated borate anions into LDHs can regulate their structure and properties, creating unique active sites and enhancing the adsorption efficiency of OH- to effectively improve the OER activity. Remarkably, the NF/Ni2P @ NiCo-BLDH electrode shows a low overpotential of 293 mV at 100 mA cm−2 for OER and a Tafel slope of 108.3 mV dec−1 in a 1.0 M KOH medium, surpassing most previously reported NiCo-based catalysts. Nevertheless, the NF/Ni2P electrode exhibits a lower overpotential for the hydrogen evolution reaction (HER) in a 1.0 M KOH medium compared to the NF/Ni2P @ NiCo-BLDH electrode. This work not only advances the catalytic activity of the NiCo-LDH-based materials in OER but also provides a new idea for large-scale electrocatalytic water splitting applications.

Spontaneous Formation of Ultrasmall Noble Metal Nanoparticles on Cobalt-Based Layered Double Hydroxide for Electrochemical and Environmental Catalysis.

Supported noble metal nanoparticles (NMNPs) are appealing for energy and environment catalysis. To facilitate the loading of NMNPs, in situ reduction of Mn+ on the support with extra reductants/surfactants is adopted, but typically results in aggregated NMNPs with uneven size distributions or blocked active sites of the NMNPs. Herein, the use of cobalt layered double hydroxide (Co-LDH) is proposed as both support and reductant for the preparation of supported NMNPs with ultrasmall sizes and even distributions. The resultant Co-LDH-supported NMNPs exhibit excellent catalytic performance and stability. For example, Ir/Co-LDH displays a low overpotential of 188mV (10mAcm-2) for electrocatalytic oxygen evolution reaction and a long-term stability over 100h (100mAcm-2) in overall water splitting. Ru/Co-LDH can achieve a 4-nitrophenol reduction with high rate of 0.36min-1 and S2- detection with low limit of detection (LOD) of 0.34µm. Overall, this work provides a green and effective strategy to fabricate supported NMNPs with greatly improved catalytic performances.

A facile synthesis of hierarchical CoFe2O4 nanosheets for efficient oxygen evolution in neutral medium

It is of great significance to develop electrocatalysts that are abundant in Earth's crust, highly efficient, and exceptionally durable for the oxygen evolution reaction (OER), particularly in neutral medium. Herein, the hierarchical CoFe2O4 nanosheets supported on iron foam (CoFe2O4/IF) were prepared by the ambient spontaneous redox reaction between iron foam and Co2+ at room temperature. The chemical composition and structure of as-prepared CoFe2O4/IF nanosheets were characterized by XRD, XPS, SEM and TEM. The CoFe2O4/IF. The as-obtained CoFe2O4/IF electrode presents excellent electrocatalytic OER activity with an overpotential of 429 mV at 10 mA cm−2 and maintains the stability of 50 h in 1 M PBS. The outstanding electrocatalytic OER activity of CoFe2O4/IF can be credited to the decreased transfer resistance and unique structural features. In addition, the CoFe2O4/IF presented here holds promise for noble-metal-free OER electrocatalyst.

Electrokinetic-mechanism of water and furfural oxidation on pulsed laser-interlaced Cu2O and CoO on nickel foam

The electrocatalytic oxidation of biomass-derived furfural (FF) feedstocks into 2-furoic acid (FA) holds immense industrial potential in optics, cosmetics, polymers, and food. Herein, we fabricated CoO/NiO/nickel foam (NF) and Cu2O/NiO/NF electrodes via in situ pulsed laser irradiation in liquids (PLIL) for the bifunctional electrocatalysis of oxygen evolution reaction (OER) and furfural oxidation reaction (FOR), respectively. Simultaneous oxidation of NF surface to NiO and deposition of CoO and/or Cu2O on NF during PLIL offer distinct advantages for enhancing both the OER and FOR. CoO/NiO/NF electrocatalyst provides a consistently low overpotential of ∼359 mV (OER) at 10 mA/cm2, achieving the maximum FA yield (∼16.37 mM) with 61.5% selectivity, 79.5% carbon balance, and a remarkable Faradaic efficiency of ∼90.1% during 2 h of FOR at 1.43 V (vs. reversible hydrogen electrode). Mechanistic pathway via in situ electrochemical-Raman spectroscopy on CoO/NiO/NF reveals the involvement of phase transition intermediates (NiOOH and CoOOH) as surface-active centers during electrochemical oxidation. The carbonyl carbon in FF is attacked by hydroxyl groups to form unstable hydrates that subsequently undergo further oxidation to yield FA products. This method holds promise for large-scale applications, enabling simultaneous production of renewable building materials and fuel.

In Situ Raman Study of Surface Reconstruction of FeOOH/Ni3S2 Oxygen Evolution Reaction Electrocatalysts.

Construction of heterojunctions is an effective strategy to enhanced electrocatalytic oxygen evolution reaction (OER), but the structural evolution of the active phases and synergistic mechanism still lack in-depth understanding. Here, an FeOOH/Ni3S2 heterostructure supported on nickel foam (NF) through a two-step hydrothermal-chemical etching method is reported. In situ Raman spectroscopy study of the surface reconstruction behaviors of FeOOH/Ni3S2/NF indicates that Ni3S2 can be rapidly converted to NiOOH, accompanied by the phase transition from α-FeOOH to β-FeOOH during the OER process. Importantly, a deep analysis of Ni─O bond reveals that the phase transition of FeOOH can regulate the lattice disorder of NiOOH for improved catalytic activity. Density functional theory (DFT) calculations further confirm that NiOOH/FeOOH heterostructure possess strengthened adsorption for O-containing intermediates, as well as lower energy barrier toward the OER. As a result, FeOOH/Ni3S2/NF exhibits promising OER activity and stability in alkaline conditions, requiring an overpotential of 268mV @ 100mAcm-2 and long-term stability over 200h at a current density of 200mAcm-2. This work provides a new perspective for understanding the synergistic mechanism of heterogeneous electrocatalysts during the OER process.

Tunable Pt-NiO interaction-induced efficient electrocatalytic water oxidation and methanol oxidation.

Metal-support interaction engineering is considered an efficient strategy for optimizing the catalytic activity. Nevertheless, the fine regulation of metal-support interactions as well as understanding the corresponding catalytic mechanisms (particularly those of non-carbon support-based counterparts) remains challenging. Herein, a controllable adsorption-impregnation strategy was proposed for the preparation of a porous nonlayered 2D NiO nanoflake support anchored with different forms of Pt nanoarchitectures, i.e. single atoms, clusters and nanoparticles. Benefiting from the unique porous architecture of NiO nanosheets, abundant active defect sites facilitated the immobilization of Pt single atoms onto the NiO crystal, resulting in NiO lattice distortion and thus changing the valence state of Pt, chemical bonding, and the coordination environment of the metal center. The synergy of the porous NiO support and the unexpected Pt single atom-NiO interactions effectively accelerated mass transfer and reduced the reaction kinetic barriers, contributing to a significantly enhanced mass activity of 5.59 A mgPt -1 at an overpotential of 0.274 V toward the electrocatalytic oxygen evolution reaction (OER) while 0.42 A mgPt -1 at a potential of 0.7 V vs. RHE for the methanol oxidation reaction (MOR) in an alkaline system, respectively. This work may offer fundamental guidance for developing metal-loaded/dispersed support nanomaterials toward electrocatalysis through the fine regulation of metal-support interactions.

Mechanochemical synthesis and application of mixed-metal copper–ruthenium HKUST-1 metal–organic frameworks in the electrocatalytic oxygen evolution reaction

Novel electrode materials for electrocatalytic hydrogen generation are investigated for increasing the activity of expensive noble-metal components.

An enhanced electrocatalytic oxygen evolution reaction by the photothermal effect and its induced micro-electric field.

Promoting better thermodynamics and kinetics of electrocatalysts is key to achieving an efficient electrocatalytic oxygen evolution reaction (OER). Utilizing the photothermal effect and micro-electric field of electrocatalysts is a promising approach to promote the sluggish OER. Herein, to reveal the relationship of the photothermal effect and its induced micro-electric field with OER performance, NiSx coupled NiFe(OH)y on nickel foam (NiSx@NiFe(OH)y/NF) is synthesized and subjected to the OER under near-infrared (NIR) light. Owing to the photothermal effect and its induced micro-electric field, the OER performance of NiSx@NiFe(OH)y/NF is significantly enhanced. Compared with no NIR light irradiation, the overpotential at 50 mA cm-2 and the Tafel slope of NiSx@NiFe(OH)y/NF under NIR light irradiation were 234.1 mV and 38.0 mV dec-1, which were lower by 12.4 mV and 7.1 mV dec-1, and it exhibited stable operation at 1.6 V vs. RHE for 8 h with 99% activity maintained. This work presents a novel inspiration to understand the photothermal effect-enhanced electrocatalytic OER.

Hollow Ru/RuO2 nanospheres with nanoparticulate shells for high performance electrocatalytic oxygen evolution reactions.

This work shows that hollow Ru/RuO2 nanoparticles having nanoparticulate shells (HN-Ru/RuO2) can be prepared using hollow microporous organic polymers with Ru species (H-MOP-Ru) as precursors. Using silica spheres as templates, H-MOPs were prepared through the Sonogashira-Hagihara coupling of 1,3,5-triethynylbenzene with 2,3-ethoxymethylenedioxy-1,4-diiodobenzene. Acid hydrolysis of cyclic ethyl orthoformate protecting groups generated catechol moieties to form H-MOP-Cat. Then, H-MOP-Ru was obtained by incorporating Ru species into H-MOP-Cat. Heat-treatment of H-MOP-Ru under air induced the formation of HN-Ru/RuO2 with a diameter of 61 nm and shells consisting of 6-7 nm nanoparticles. Due to the hollow structure and nanoparticulate shells, HN-Ru/RuO2 showed a high surface area of 80 m2 g-1 and a pore volume of 0.18 cm3 g-1. The HN-Ru/RuO2 showed enhanced electrocatalytic performance for the oxygen evolution reaction (OER) with an overpotential of 295 mV @ 10 mA cm-2 and a Tafel slope of 46 mV dec-1 in alkaline electrolyte, compared with control RuO2 such as commercial Ru/RuO2 nanoparticles (A-Ru/RuO2) and home-made Ru/RuO2 nanoparticles (N-Ru/RuO2) prepared via the same synthetic procedure as HN-Ru/RuO2. While HN-Ru/RuO2 inevitably contained Pd originated from coupling catalysts, it showed superior performance to Ru/RuO2 nanoparticles with the same Pd content (N1-Ru/RuO2), indicating that the efficient electrocatalytic performance of HN-Ru/RuO2 is attributable to its hollow structure and nanoparticulate shells.

A series of isostructural metal-organic frameworks for an enhanced electro-catalytic oxygen evolution reaction.

Three new isostructural MOFs (ZnTIA, CoTIA and CdTIA) were synthesized by the solvothermal synthesis of the organic linker 5-triazole isophthalic acid (5-TIA) with the transition metals Zn(II), Co(II) and Cd(II) in the presence of the structure directing agent tetramethyl ammonium chloride (TMA). These three MOFs were characterized thoroughly by ScXRD, PXRD, FT-IR, TGA, BET and SEM. They have excellent thermal and water stabilities. Among all these MOFs mentioned, pristine CoTIA exhibited excellent electrocatalytic activity toward the oxygen evolution reaction (OER). It exhibits a Tafel slope of 68.9 mV dec-1 with an overpotential of 337 mV at 10 mA cm-2 current density. The OER activity of the CoTIA MOF is relatively equivalent to that of the state-of-the-art catalyst (RuO2). Furthermore, the mechanical stability of crystalline ZnTIA, CoTIA and CdTIA MOFs was tested under ball mill pressure. The result showed that all the MOFs exhibit low tolerance to mechanical force because their structure was highly distorted or collapsed under such pressure, which is reflected by their poor electrocatalytic OER activity.

Recent progress of Ni-based nanomaterials for the electrocatalytic oxygen evolution reaction at large current density.

The precise design and development of high-performing oxygen evolution reaction (OER) for the production of industrial hydrogen gas through water electrolysis has been a widely studied topic. A profound understanding of the nature of electrocatalytic processes reveals that Ni-based catalysts are highly active toward OER that can stably operate at a high current density for a long period of time. Given the current gap between research and applications in industrial water electrolysis, we have completed a systematic review by constructively discussing the recent progress of Ni-based catalysts for electrocatalytic OER at a large current density, with special focus on the morphology and composition regulation of Ni-based electrocatalysts for achieving extraordinary OER performance. This review will facilitate future research toward rationally designing next-generation OER electrocatalysts that can meet industrial demands, thereby promoting new sustainable solutions for energy shortage and environment issues.

Silver-integrated cobalt hydroxide hybrid nanostructured materials for improved electrocatalytic oxygen evolution reaction

Synthesizing Co(OH)2 with coexisting amorphous and crystalline phases showed strong electrocatalytic OER activity in the alkaline medium. The OER activity of Co(OH)2 was further improved upon the integration of AgNPs.

Harnessing the electronic structure of active metals to lower the overpotential of the electrocatalytic oxygen evolution reaction.

Despite substantial advancements in the field of the electrocatalytic oxygen evolution reaction (OER), the efficiency of earth-abundant electrocatalysts remains far from ideal. The difficulty stems from the complex nature of the catalytic system, which limits our fundamental understanding of the process and thus the possibility of a rational improvement of performance. Herein, we shed light on the role played by the tunable 3d configuration of the metal centers in determining the OER catalytic activity by combining electrochemical and spectroscopic measurements with an experimentally validated computational protocol. One-dimensional coordination polymers based on Fe, Co and Ni held together by an oxonato linker were selected as a case study because of their well-defined electronic and geometric structure in the active site, which can be straightforwardly correlated with their catalytic activity. Novel heterobimetallic coordination polymers were also considered, in order to shed light on the cooperativity effects of different metals. Our results demonstrate the fundamental importance of electronic structure effects such as metal spin and oxidation state evolutions along the reaction profile to modulate ligand binding energies and increase catalyst efficiency. We demonstrated that these effects could in principle be exploited to reduce the overpotential of the electrocatalytic OER below its theoretical limit, and we provide basic principles for the development of coordination polymers with a tailored electronic structure and activity.

An in situ formed ZIF-67 derived NiFeCo-P nano-array for accelerating the electrocatalytic oxygen evolution reaction

Phosphating ternary nickel/iron/cobalt hybrid nano-arrays (NiFeCo-P) synthesized by three steps of impregnation, hydrothermal reaction and phosphating calcination exhibits low overpotential, good kinetics and high structural stability.

Electronic modulation of iridium single atomic sites on NiCr layered double hydroxide for an improved electrocatalytic oxygen evolution reaction

A rational approach to understand the catalytic superiority of Ir1/NiCr LDH single atom catalyst over state-of-art IrO2 for oxygen evolution reaction via electronic modulation effect of single atomic sites.