Electrochemical Oxygen Evolution Reaction Research Articles

Pluronic-123 Assisted Synthesis of Cobalt Vanadate Microparticles (µ-CoV MPs) for Durable Electrochemical Oxygen Evolution Reaction in Seawater and Connate Water

Exploring different catalytic material paradigms could drive the search for the best oxygen evolution reaction (OER) catalyst to achieve industrially-feasible hydrogen fuel from water. Cobalt-based materials are considered good choices in this regard. Herein, we synthesized Pluronic-123 (P-123)-stabilized, unique, rough, globular-shaped cobalt vanadate microparticles (µ-CoV MPs) using an ultrasonic-assisted solvothermal method. The as-synthesized µ-CoV MPs were subjected to high-temperature annealing to improve the crystallinity and the surface polymer moieties were pyrolyzed. Conventional SEM, XRD, FTIR, and BET analyses evaluated the morphological and structural features. The temperature-controlled crystalline phase led to extensive OER performance in SW electrolytes. The OER onset potential (VOER) was observed at 1.557 V@10 mA/cm2 in seawater (SW) for µ-CoV MPs annealed at 400 °C compared to the VOER of 1.632 V of non-annealed µ-CoV MPs. The current density showed a steep increase beyond 1.557 V, confirming the excellent electrokinetics OER behavior of the µ-CoV MPs-deposited electrode. The chronoamperometric (I–t) OER stability comparison in SW and connate water (CW) electrolytes indicated only a <20% initial current density decrease after 8 h in the case of the SW electrolyte. However, the CW electrolyte posed serious challenges to the electrode and activity was completely lost after <2 h. The electrolytic comparison indicated that SW is highly suitable for µ-CoV MPs electrodes.

Impact of Highly Concentrated Alkaline Treatment on Mesostructured Cobalt Oxide for the Oxygen Evolution Reaction

AbstractCommercial alkaline water electrolysis cells typically use highly concentrate KOH as electrolyte, which strongly influences alteration of catalyst and its performance. Herein, the impact of alkaline treatment toward the structural alteration and electrochemical oxygen evolution reaction (OER) activity of well‐defined ordered mesoporous Co3O4 is systematically studied. The overall morphology of mesostructured Co3O4 is relatively resilient to the exposure of highly concentrated alkaline solution up to 13 m KOH. The spectroscopic analyses, including in situ diffuse reflectance infrared spectroscopy, reveal the presence of carbonate‐based species after the alkaline treatment due to impurities of the commercial KOH. The pre‐treated samples exhibit a higher electrochemically active surface area, decreased charge transfer resistance, and increased current density from 103 to 155 mA cm−2 at 1.7 V versus RHE. The in situ electrochemical Raman spectroscopy investigation supports formation of active CoOOH phase on KOH pre‐treated Co3O4, which might play a key role toward enhanced OER activity.

Engineering high-spin state cobalt cations in spinel ZnCo2O4 for spin channel propagation and electrocatalytic activity enhancement in Li-O2 battery

Spinel zinc cobalt oxide (ZnCo2O4) is considered as the promising electrocatalyst for the electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, theoretical calculations uncovered that the presence of low-spin (LS) state cobalt cations impedes the electrocatalytic activity of ZnCo2O4 because the t2g6eg0 configuration yields purely localized electronic structure with poor binding affinity with reaction intermediate. By regulating the spin state of cobalt cations in ZnCo2O4, spin-selected charge transfer is boosted during ORR/OER processes due to the propagated spin channel, thus causing abundant active sites for intermediates adsorption. Experimental results show that increasing calcination temperature during the synthesis process is an operable method to fabricate high-spin (HS) cobalt cations in ZnCo2O4. And the Li-O2 battery with ZnCo2O4 containing high-spin cobalt cations shows remarkably low overpotential of only 0.45 V and excellent durability of more than 800 h. This work underlines the critical role of the electron spin state in facilitating oxygen redox reactions on transition metal oxides.

Pomegranate-like Ni-doped cobalt boride implanted in B, N-doped carbon nanocages for enhanced electrochemical oxygen evolution

The development of efficient and stable transition metal boride electrocatalysts for oxygen evolution reaction (OER) is critical for energy conversion and environmental protection. Herein, we synthesized B, N-doped carbon layer encapsulated the Ni-doped CoxB nanocages electrocatalyst (denoted as Ni-CoxB@BNC) via a high-temperature boronizing, derived from Ni-doped cobalt-based zeolite imidazole frame (NiCo-ZIF), toward enhanced electrochemical alkaline oxygen evolution reaction. The Ni-CoxB@BNC electrocatalyst synthesized at 550 °C exhibits excellent OER activity with a low overpotential of 274 mV and a Tafel slope of 80 mV dec−1 at a current density of 10 mA cm−2, which is better than precious metal RuO2. The synergistic effect between B, N-doped carbon layer and Ni-doped CoxB in Ni-CoxB@BNC leads to higher OER catalytic activity. The B, N-doped carbon layer provides additional active sites, which accelerates charge transport and enhances the conductivity of Ni-CoxB@BNC during OER. In addition, it also protects the pomegranate seed-like Ni-CoxB nanoparticles inside, improving the stability of the Ni-CoxB@BNC material. This work unambiguously elucidates the design and preparation strategy of transition metal boride implanted B, N-doped carbon nanocage electrocatalysts derived from controlled bimetallic ZIF precursor.

Ruthenium Azobis(benzothiazole): Electronic Structure and Impact of Substituents on the Electrocatalytic Single-Site Water Oxidation Process

The present article deals with the structurally and spectroelectrochemically characterized newer class of ruthenium-azoheteroarenes [RuII(Ph-trpy)(Cl)(L)]ClO4, [1]ClO4-[3]ClO4 (Ph-trpy: 4'-phenyl-2,2':6',2″-terpyridine; L1: 2,2'-azobis(benzothiazole) ([1]ClO4); L2: 2,2'-azobis(6-methylbenzothiazole) ([2]ClO4); L3: 2,2'-azobis(6-chlorobenzothiazole) ([3]ClO4)). A collective consideration of experimental (i.e., structural and spectroelectrochemical) and theoretical (DFT calculations) results of [1]ClO4-[3]ClO4 established selective stabilization of (i) the unperturbed azo (N═N)0 function of L, (ii) the exclusive presence of the isomeric form involving the N(azo) donor of L trans to Cl, and (iii) the presence of extended, hydrogen-bonded trimeric units in the asymmetric unit of [2]ClO4 (CH---O) via the involvement of ClO4- anions. The detailed electrochemical studies revealed metal-based oxidation of [RuII(Ph-trpy)(Cl)(L)]+ (1+-3+) to [RuIII(Ph-trpy)(Cl)(L)]2+ (12+-32+); however, the electronic form of the first reduced state (1-3) could be better represented by its mixed RuII(Ph-trpy)(Cl)(L•-)/RuIII(Ph-trpy)(Cl)(L2-) state. Both native (1+-3+) and reduced (1-3) states exhibited weak lower energy transitions within the range of 1000-1200 nm. Further, [1]ClO4-[3]ClO4 delivered an electrochemical OER (oxygen evolution reaction) process in alkaline medium on immobilizing them to a carbon cloth support, which divulged an amplified water oxidation feature for [2]ClO4 due to the presence of electron-donating methyl groups in the L2 backbone. The faster OER kinetics and high catalytic stability of [2]ClO4 could also be rationalized by its lowest Tafel slope (85 mV dec-1) and choronoamperometric experiment (stable up to 12 h), respectively, along with high Faradic efficiency (∼97%). A comparison of [2]ClO4 with the reported analogous ruthenium complexes furnished its excellent intrinsic water oxidation activity.

Amorphous Metal-Organic Framework-Derived Electrocatalyst to Boost Water Oxidation.

Amorphous metal-organic framework (MOF) materials have drawn extensive interest in the design of high-performance electrocatalysts for use in the electrochemical oxygen evolution reaction. However, there are limitations to the utilization of amorphous MOFs due to their low electrical conductivity and unsatisfactory stability. Herein, a novel amorphous-crystalline (AC) heterostructure is successfully constructed by synthesizing a crystalline metal sulfide (MS)-embedded amorphous Ni0.67Fe0.33-MOF, namely an MS/Ni0.67Fe0.33-MOF. It exhibits excellent catalytic performance (a low overpotential of 248 mV at 10 mA cm-2 with a small Tafel slope of 50 mV decade-1), durability, and stability (only 8% degradation of the current density at a constant voltage after 24 h). This work thus sheds light on the engineering of highly efficient catalysts with AC heterointerfaces for optimizing water-splitting systems.

Cobalt carbonate hydroxide assisted formation of self-supported CoNi-based Metal–Organic framework nanostrips as efficient electrocatalysts for oxygen evolution reaction

The development of efficient and low-cost electrocatalysts is crucial for improving the efficiency of electrochemical oxygen evolution reaction (OER). Herein, self-supported CoNi-based metal-organic framework (MOF) nanostrips grown on Ni foam (NF) were synthesized with cobalt carbonate hydroxide (CoCH) nanoneedles as a sacrificial template and demonstrated to be highly efficient electrocatalysts for OER. In this approach, the CoCH nanoneedles play a key role in modulating the morphology of CoNi-MOF with reduced thickness and sizes through affording Co source and slowing down the leaching of Ni ions from the NF substrate. The resultant CoNi-MOF/CoCH/NF electrode possesses higher catalytically active surface area and smaller electrochemical impedance than CoCH template-free electrodes, which enable rapid mass transport and charge transfer during OER, thus showing enhanced electrocatalytic activity for OER. In alkaline media (1.0 M KOH), it needs a low overpotential of 251 mV to deliver a current density of 10 mA cm−2 and exhibits a small Tafel slope of 40.7 mV dec−1 as well as excellent durability. The developed approach may inspire further capability on constructing more promising catalysts for energy related applications.

Improved OER catalytic performance of NiFe-LDH with hydrothermal carbonization microspheres

The electrochemical oxygen evolution reaction (OER) is a fundamental anodic semi-reaction used in the hydrogen energy industry. Herein, we report a novel NiFe-layered double hydroxide (NiFe-LDH)-based hybrid catalyst for the OER, which is promoted by the two-step hydrothermal loading of carbon sphere (CS) onto NiFe-LDH sheets, named as NiFe-LDH@CS. The effects of hydrothermal carbonization (HTC) parameters (such as hydrothermal time and glucose concentration) and the loading ratio of CSs on NiFe-LDH@CS were investigated. The results showed that the two-step hydrothermal synthesis significantly inhibited the interference of the carbonized substances on the lattice formation of NiFe-LDH and successfully achieved a firm combination. By adjusting the HTC process, the surface characteristics and graphitization degree of the carbonized microspheres can be effectively controlled, leading to increased OER performance of NiFe-LDH@CS. Thus, under the optimal process parameters (5 h, 0.6 M, and 5 mL), NiFe-LDH@CS exhibited an excellent overpotential of 292 mV at 50 mA cm-2 and 372 mV at 100 mA cm-2 for the OER. The outstanding OER performance of NiFe-LDH@CS is attributed to the excellent morphology control of the composite, abundant functional groups, and suitable graphitization degree of the hydrothermally carbonized CS, as well as the synergistic effect between the CSs and NiFe-LDH.

Ball milling as an effective method for improving oxygen evolution reaction electrocatalyst Ca3Co4O9

Misfit-layered Ca3Co4O9 was investigated as oxygen evolution reaction catalyst for electrochemical water splitting. Oxygen vacancies can be effectively induced by ball milling as detected by electronic paramagnetic resonance and X-ray photoelectron spectrometer measurements. The electrochemical performance was investigated for the Ca3Co4O9 catalysts with different ball milling times. The results show that the sample with the ball milling time of 24 h possesses the best performance due to the induced oxygen vacancies as well as the enhanced specific surface area. This work will provide an effective route to improve the electrochemical oxygen evolution reaction performance of the misfit-layered cobaltates.

Role of Ir Decoration in Activating a Multiscale Fractal Surface in Porous Ni for the Oxygen Evolution Reaction

Interfacial engineering of electrocatalysts is a pivotal approach for promoting the energy conversion efficiency of water electrolysis systems. Anchoring clusters or even single atoms of a foreign element on the surface of a support, usually 3D structured, can alter its local electronic structure leading to superior electrocatalytic activity. Herein, we report a method to decorate a 3D fractal Ni electrode with Ir atoms via a galvanic displacement reaction. The resulting electrode has a very low Ir loading of 1.6 μmole cmgeo–2, with iridium atoms present as 4–5 nm diameter nanoclusters on the electrode surface. The activity for the electrochemical oxygen evolution reaction (OER) of the 3D fractal Ni electrode was improved by decoration with Ir, resulting in an overpotential of 195 mV at 10 mA cm–2 and a Tafel slope of 44 mV dec–1. Apart from increasing the electrocatalytic activity for the OER due to the very presence of more active iridium atoms, the galvanic displacement reaction resulted in a factor 8–10 increase of the electrochemically active surface area due to the creation/activation of a secondary pore structure that contributes also to the better electrocatalytic performance of the resulting electrode. Using operando acoustic emission, it is demonstrated that the galvanic displacement reaction and the presence of Ir nanoclusters have the additional effect of reducing the average O2 bubble size formed during the OER. As a result, the blocking effect of O2 bubbles at high current density is less drastic than on the 3D fractal Ni electrode, resulting in a less severe decrease of the electrochemically active area at large current density. All three effects contribute toward improving the OER performance of the Ir-decorated 3D fractal Ni electrode.

Enhanced Activity of Enzyme Immobilized on Hydrophobic ZIF-8 Modified by Ni2+ Ions.

The development of efficient enzyme immobilization to promote their recyclability and activity is highly desirable. Zeolitic imidazolate framework-8 (ZIF-8) has been proved to be an effective platform for enzyme immobilization due to its easy preparation and biocompatibility. However, the intrinsic hydrophobic characteristic hinders its further development in this filed. Herein, a facile synthesis approach was developed to immobilize pepsin (PEP) on the ZIF-8 carrier by using Ni2+ ions as anchor (ZIF-8@PEP-Ni). By contrast, the direct coating of PEP on the surface of ZIF-8 (ZIF-8@PEP) generated significant conformational changes. Electrochemical oxygen evolution reaction (OER) was employed to study the catalytic activity of immobilized PEP. The ZIF-8@PEP-Ni composite attains remarkable OER performance with an ultralow overpotential of only 127 mV at 10 mA cm-2 , which is much lower than the 690 and 919 mV overpotential values of ZIF-8@PEP and PEP, respectively.

Enhanced Activity of Enzyme Immobilized on Hydrophobic ZIF‐8 Modified by Ni2+ Ions

AbstractThe development of efficient enzyme immobilization to promote their recyclability and activity is highly desirable. Zeolitic imidazolate framework‐8 (ZIF‐8) has been proved to be an effective platform for enzyme immobilization due to its easy preparation and biocompatibility. However, the intrinsic hydrophobic characteristic hinders its further development in this filed. Herein, a facile synthesis approach was developed to immobilize pepsin (PEP) on the ZIF‐8 carrier by using Ni2+ ions as anchor (ZIF‐8@PEP‐Ni). By contrast, the direct coating of PEP on the surface of ZIF‐8 (ZIF‐8@PEP) generated significant conformational changes. Electrochemical oxygen evolution reaction (OER) was employed to study the catalytic activity of immobilized PEP. The ZIF‐8@PEP‐Ni composite attains remarkable OER performance with an ultralow overpotential of only 127 mV at 10 mA cm−2, which is much lower than the 690 and 919 mV overpotential values of ZIF‐8@PEP and PEP, respectively.

Reduced graphene oxide encapsulated perovskite-type lanthanum cobalt oxide nanoparticles for efficient electrolysis of water to oxygen reactions (OER/ORR)

Developing high-performance non-precious electro-catalysts for water splitting reactions is important for energy conversion applications. In this study, reduced graphene oxide encapsulated perovskite-type lanthanum cobalt oxide nanoparticles (LaCoO3@rGO) have been fabricated as highly efficient electro-catalysts by ultra-sonication process for electrochemical oxygen evolution and reduction reactions (OER/ORR) in O2 – saturated alkaline medium (1.0 M KOH). The characterization techniques indicated that the targeted materials were formed with controlled support by rGO sheets to the nanoparticles. The LaCoO3@rGO nanocomposites show improved electro-catalytic performance to OER with lower over-potential (280 mV at ƞ10) and Tafel slopes (104 mV/dec) compared with pure LaCoO3 electro-catalyst. The electro-chemical ORR reactions of the prepared electrodes were monitored by the rotating disk electrode (RDE) measurements. The LaCoO3@rGO electro-catalyst shows 4e- system in ORR at all potentials (i.e. from 0.2 V to 0.5 V), while LaCoO3 electro-catalyst shows 4e- system only at low potentials (i.e. 0.2 V and 0.3 V). Moreover, the stability of the electrodes was also tested by the chronoamperometry (CA) and cyclic stability measurements for the commercial purpose. Our research will open new windows for developing the non-precious electro-catalysts in clean energy applications.

SERS Reveals the Presence of Au–O–O–H and Enhanced Catalytic Activity of Electrochemically Dealloyed AgAu Nanoparticles

Due to their high surface-to-volume ratio and large proportion of low coordinated surface atoms, dealloyed nanoparticles have gained increasing attention as porous catalysts for the electrochemical oxygen evolution reaction (OER). Here, we characterize and rationalize the physical and chemical properties of operando gold-enriched porous nanoparticles fabricated by electrochemical dealloying of citrate-capped silver gold alloy nanoparticles in 250 mM KNO3. We combine surface-enhanced Raman spectroscopy (SERS) with electrochemistry for catalyst tracking. With SERS, we observe at 1.05 V (vs platinum quasi-reference electrode) the formation of Au–O–O–H species, a known intermediate of OER, while this is not observed for monometallic gold nanoparticles or bare electrodes. In agreement, qualitative measurements of the catalytic activity prove that appreciable OER currents are detected at lower potentials for gold-enriched porous nanoparticles compared to gold nanoparticles of the same size. Our results pave the way for the application of dealloying-derived nanoparticles as promising catalyst materials.

Slow O–H Dissociation in the First-Order Oxygen Evolution Reaction Kinetics on Polycrystalline γ-FeO(OH)

To unravel the reaction mechanism of the electrochemical oxygen evolution reaction (OER), analysis of the intrinsic activity parameters obtained via electrokinetic investigation remains effective. In this study, polycrystalline γ-FeO(OH), synthesized at room temperature, was used as a stable, albeit reactive, anode for OER, and electrokinetic studies were performed to unravel the oxygen evolution reaction pathway. The cell temperature, hydroxyl ion concentration, and the cation of the supporting electrolyte were varied, and the influence of external bias on the OER activity was recorded. Changes in the cell temperature from 30 to 65 °C lead to an enhanced OER activity due to small overpotential, Tafel slope, and charge-transfer resistance (Rct) values at high temperatures, which unambiguously highlights the influence of the thermodynamic barrier and electron-transfer kinetics. The calculated anodic charge-transfer coefficient (αa) and specific exchange current density (j0,s) values are 0.65 and 2.24 × 10–5 mA cm–2, respectively. The faster OER kinetics on polycrystalline γ-FeO(OH) can also be attributed to an appreciably low activation energy of 8.26 ± 2 kJ mol–1, where variation of the electrolyte concentration indicated a first-order dependence on [OH]−. Experimentally obtained intrinsic kinetic parameters such as the Tafel slope, anodic charge-transfer coefficient, exchange current density, activation energy (Ea), reaction order (m), and deuterium isotope effect implicate the dissociation of hydroxyl ions on the polycrystalline γ-FeO(OH) as the rate-determining step. The direct effect of cations such as Li+, Na+, and K+ of the electrolyte on OER highlights a weak interaction of the cations with the surface-active [FeIII-OH] species. A change in the electrode substance from three-dimensional highly conductive nickel foam (NF) to two-dimensional less conductive carbon cloth (CC) resulted in a change in the slow step, leading to the formation of a high-valency iron oxo intermediate from the iron hydroxy species.

On the role of graphene oxide in bifunctional Ni/MOF/rGO composites in electrochemical nitrate detection and oxygen evolution reaction

Bi-functional metal organic frameworks as promising porous framework hybrid materials for electrochemical nitrate sensing and oxygen evolution reaction.

Nanoflower electrocatalysts derived from mixed metal (Fe/Co/Ni) organic frameworks for the electrochemical oxygen evolution reaction

Trimetal MOFs have been synthesized based on C8H7NO4 by changing the ratio of Fe/Co/Ni and used directly in electrocatalytic OER. Among them, NiCoFe-MOF-2 exhibits excellent OER catalytic performance due to its unique layered structure.

NiCo2O4 nano-needles as an efficient electro-catalyst for simultaneous water splitting and dye degradation.

Developing an efficient and non-precious bifunctional catalyst capable of performing water splitting and organic effluent degradation in wastewater is a great challenge. This article reports an efficient bifunctional nanocatalyst based on NiCo2O4, synthesized using a simple one-pot co-precipitation method. We optimized the synthesis conditions by varying the synthesis pH and sodium dodecyl sulfate (SDS) concentrations. The prepared catalyst exhibited excellent catalytic activity for the electrochemical oxygen evolution reaction (OER) and simultaneous methylene blue (MB) dye degradation. Among the catalysts, the catalyst synthesized using 1 g SDS as a surfactant at 100 °C provided the highest current density (658 mA cm-2), lower onset potential (1.34 V vs. RHE), lower overpotential (170 mV @ 10 mA cm-2), and smallest Tafel slope (90 mV dec-1) value. Furthermore, the OH˙ radicals produced during the OER electrochemically degraded the MB to 90% within 2 hours. The stability test conducted at 20 mA cm-2 showed almost negligible loss of the electrochemical response for OER, with 99% retention of the original response. These results strongly suggest that this catalyst is a promising candidate for addressing the challenges of wastewater treatment and energy generation.

Facile Fabrication of Ni9 S8 /Ag2 S Intertwined Structures for Oxygen and Hydrogen Evolution Reactions.

Here, we report the fabrication of the unique intertwined Ni9 S8 /Ag2 S composite structure with hexagonal shape from their molecular precursors by one-pot thermal decomposition. Various spectroscopic and microscopic techniques were utilized to confirm the Ni9 S8 /Ag2 S intertwined structure. Powder X-ray Powder Diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis suggest that there is an enrichment of Ni9 S8 phase in Ni9 S8 /Ag2 S. The presence of Ag2 S in Ni9 S8 /Ag2 S improves the conductivity by reducing the interfacial energy and charge transfer resistance. When Ni9 S8 /Ag2 S is employed as an electrocatalyst for electrochemical oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity, it requires a low overpotential of 152 mV for HER and 277 mV for OER to obtain the geometrical current density of 10 mA cm-2 , which is definitely superior to that of its components Ni9 S8 and Ag2 S. This work provides a simple design route to develop an efficient and durable electrocatalyst with outstanding OER and HER performance and the present catalyst (Ni9 S8 /Ag2 S) deserves as a potential candidate in the field of energy conversion systems.

Controlling the terminal layer atom of InTe for enhanced electrochemical oxygen evolution reaction and hydrogen evolution reaction performance.

Herein, we report the method of molecular-beam-epitaxial growth (MBE) for precisely regulating the terminal surface with different exposed atoms on indium telluride (InTe) and studied the electrocatalytic performances toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The improved performances result from the exposed In or Te atoms cluster, which affects the conductivity and active sites. This work provides insights into the comprehensive electrochemical attributes of layered indium chalcogenides and exhibits a new route for catalyst synthesis.