Integrating hydrogen production with anodic selective oxidation of sulfides over a CoFe layered double hydroxide electrode

Replacing the sluggish oxygen evolution reaction (OER) with oxidation reactions for the synthesis of complex pharmaceutical molecules coupled with enhanced hydrogen evolution reaction (HER) is highly attractive, but it is rarely explored. Here, we report an electrochemical protocol for selective oxidation of sulfides to sulfoxides over a CoFe layered double hydroxide (CoFe-LDH) anode in an aqueous-MeCN electrolyte, coupled with 2-fold promoted cathodic H₂ productivity. This protocol displays high activity (85–96% yields), catalyst stability (10 cycles), and generality (12 examples) in selective sulfide oxidation. We demonstrate its applicability in the synthesis of four important pharmaceutical related sulfoxide compounds with scalability (up to 1.79 g). X-ray spectroscopy investigations reveal that the CoFe-LDH material evolved into amorphous CoFe-oxyhydroxide under catalytic conditions. This work may pave the way towards sustainable organic synthesis of valuable pharmaceuticals coupled with H₂ production.

Replacing anodic OER with selective sulfide oxidation produces sulfoxide-related pharmaceutical compounds over a CoFe-LDH catalyst with enhanced HER, providing a sustainable protocol for valuable pharmaceuticals synthesis without external oxidants.     

Chromium-Doped Nickel Oxide and Nickel Nitride Mediate Selective Electrocatalytic Oxidation of Sterol Intermediates Coupled with H2 Evolution

Replacing the oxygen evolution reaction (OER) with the thermodynamically favorable electrooxidation of organics is considered a promising approach for the simultaneous production of hydrogen (H₂) and high-value chemicals. However, exploring and optimizing efficient electrocatalysts remains a challenge for large-scale production of value-added steroid carbonyl and H₂. Herein, Cr-NiO/GF and Cr-Ni₃N/GF (GF: graphite felt) electrocatalysts were designed as anode and cathode for the production of steroid carbonyls and H₂, respectively. The cooperative Cr-NiO and ACT (4-acetamido-2,2,6,6-tetramethyl-1-piperidine-N-oxyl) electrocatalyst can be extended to the electrooxidation of a series of steroid alcohols to the corresponding aldehydes. Additionally, Cr-Ni₃N displays superior electrocatalytic activity for hydrogen evolution reaction (HER), with a low overpotential of 35 mV to deliver 10 mA cm⁻². Furthermore, the system coupled with anodic electrooxidation of sterol and cathodic HER exhibited excellent performance with high space-time yield of 48.85 kg m⁻³ h⁻¹ for steroid carbonyl and 1.82 L h⁻¹ for H₂ generation in a two-layer stacked flow cell. Density Functional Theory (DFT) calculations indicated that Cr doping effectively stabilizes ACTH on the NiO surface, and ACTH molecule could be captured via the ketonic oxygen interaction with Cr, resulting in excellent electrocatalytic activity. This work develops a novel approach to the rational design of efficient electrocatalysts for the simultaneous production of H₂ and large-scale value-added pharmaceutical carbonyl intermediates.     

Phosphate-induced interfacial electronic engineering in VPO4-Ni2P heterostructure for improved electrochemical water oxidation

Anodic oxygen evolution reaction（OER） is the key bottleneck for water electrolysis technique owing to its sluggish reaction kinetics. Interfacial engineering on the rationally designed heterostructure can regulate the electronic states efficiently for intrinsic activity improvement. Here, we report a co-phosphorization approach to construct a VPO₄-Ni₂P heterostructure on nickel foam with strongly chemical binding,wherein phosphate acts as electronic modifier for Ni₂     

Nickel-iron borate coated nickel-iron boride hybrid for highly stable and active oxygen evolution electrocatalysis

The development of efficient and cost-effective electrocatalysts toward anodic oxygen evolution reaction (OER) is crucial for the commercial application of electrochemical water splitting. As the most promising electrocatalysts, the OER performances of nickel-iron-based materials can be further improved by introducing metalloid elements to modify their electron structures. Herein, we developed an efficient hybrid electrocatalyst with nickel-iron boride (NiFeB) as core and amorphous nickel-iron borate (NiFeB_i) as shell (NiFeB@NiFeB_i) via a simple aqueous reduction. The obtained NiFeB@NiFeB_i exhibits a small overpotential of 237 mV at 10 mA/cm² and Tafel slope of 57.65 mV/dec in 1.0 mol/L KOH, outperforming most of the documented precious-metal-free based electrocatalysts. Benefiting from the in situ formed amorphous NiFeBi layer, it shows excellent stability toward the oxygen evolution reaction (OER). These findings might provide a new way to design advanced precious-metal-free electrocatalysts for OER and the application of electrochemical water splitting.     

Molybdenum-induced tuning 3d-orbital electron filling degree of CoSe2 for alkaline hydrogen and oxygen evolution reactions

The development of high-performance non-precious metal-based robust bifunctional electrocatalyst for both hydrogen evolution reaction(HER) and oxygen evolution reactions(OER) in alkaline media is essential for the electrochemical overall water splitting technologies. Herein, we demonstrate that the HER/OER performance of Co Se₂ can be significantly enhanced by tuning the 3d-orbital electron filling degree through Mo doping. Both density functional theory(DFT) calculations and experime...     

The InSe/g-CN van der Waals hybrid heterojunction as a photocatalyst for water splitting driven by visible light

Designing and developing the highly efficient photocatalysts is full of significance to achieve spontaneous photolysis water. In this work, using the first-principles calculations, we have performed a systematic theoretical study of water splitting photocatalytic activity of the InS e/g-CN heterojunction. It is concluded that the In Se/g-CN heterojunction is a typical type-II semiconductor, whose electrons and holes can be effectively separated. And the potential of the conduction band minimum（C...     

Advanced Bifunctional Oxygen Reduction and Evolution Electrocatalyst Derived from Surface-Mounted Metal–Organic Frameworks

Metal–organic frameworks (MOFs) and their derivatives are considered as promising catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which are important for many energy provision technologies, such as electrolyzers, fuel cells and some types of advanced batteries. In this work, a “strain modulation” approach has been applied through the use of surface-mounted NiFe-MOFs in order to design an advanced bifunctional ORR/OER electrocatalyst. The material exhibits an excellent OER activity in alkaline media, reaching an industrially relevant current density of 200 mA cm⁻² at an overpotential of only ≈210 mV. It demonstrates operational long-term stability even at a high current density of 500 mA cm⁻² and exhibits the so far narrowest “overpotential window” ΔE_ORR-OER of 0.69 V in 0.1 m KOH with a mass loading being two orders of magnitude lower than that of benchmark electrocatalysts.     

Trapped interfacial redox introduces reversibility in the oxygen reduction reaction in a non-aqueous Ca2+ electrolyte

Electrochemical investigations of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been conducted in a Ca²⁺-containing dimethyl sulfoxide electrolyte. While the ORR appears irreversible, the introduction of a tetrabutylammonium perchlorate (TBAClO₄) co-salt in excess concentrations results in the gradual appearance of a quasi-reversible OER process. Combining the results of systematic cyclic voltammetry investigations, the degree of reversibility depends on the ion pair competition between Ca²⁺ and TBA⁺ cations to interact with generated superoxide (O₂⁻). When TBA⁺ is in larger concentrations, and large reductive overpotentials are applied, a quasi-reversible OER peak emerges with repeated cycling (characteristic of formulations without Ca²⁺ cations). In situ Raman microscopy and rotating ring-disc electrode (RRDE) experiments revealed more about the nature of species formed at the electrode surface and indicated the progressive evolution of a charge storage mechanism based upon trapped interfacial redox. The first electrochemical step involves generation of O₂⁻, followed primarily by partial passivation of the surface by Ca_xO_y product formation (the dominant initial reaction). Once this product matrix develops, the subsequent formation of TBA⁺--O₂⁻ is contained within the Ca_xO_y product interlayer at the electrode surface and, consequently, undergoes a facile oxidation reaction to regenerate O₂.

An interlayer product of oxygen reduction with Ca²⁺/TBA⁺ yields a quasi-reversible oxygen evolution reaction by inducing a trapped interfacial redox process.     

N-doped graphitic carbon encapsulating cobalt nanoparticles derived from novel metal–organic frameworks for electrocatalytic oxygen evolution reaction

Nitrogen-doped carbon catalysts with hierarchical porous structure are promising oxygen evolution reaction (OER) catalysts due to the faster mass transfer and better charge carrying ability. Herein, an exquisite high nitrogen-containing ligand was designed and readily synthesized from the low-cost biomolecule adenine. Accordingly, three new MOFs (TJU-103, TJU-104 and TJU-105) were prepared using the Co(II) or Mn(II) ions as metal nodes. Through rationally controlling pyrolysis condition, in virtue of the high nitrogen content in well-defined periodic structure of the pristine MOFs, TJU-104–900 among the derived MOFs with hierarchical porous structure, i.e., N-doped graphitic carbon encapsulating homogeneously distributed cobalt nanoparticles, could be conveniently obtained. Thanks to the synergistic effect of the hierarchical structure and well dispersed active components (i.e., C=O, Co‒N_x, graphitic C and N, pyridinic N), it could exhibit an overpotential of 280 mV@10 mA/cm² on carbon cloth for OER activity. This work provides the inspiration for fabrication of nitrogen-doped carbon/metal electrocatalysts from cost-effective and abundant biomolecules, which is promising for practical OER application.     

Boosting electrochemical hydrogen evolution by coupling anodically oxidative dehydrogenation of benzylamine to benzonitrile

The electricity-driven water splitting acts as a promising pathway for renewable energy conversion and storage, yet anodic oxygen evolution reaction (OER) largely hinders its efficiency. Seeking the alternatives to OER exhibits the competitive advance to address this predicament. In this work, we show a more thermodynamically and kinetically favorable reaction, electrochemical oxidative dehydrogenation (EODH) of benzylamine to replace the conventional OER, catalyzed by a cobalt cyclotetraphosphate (Co₂P₄O₁₂) nanorods catalyst grown on nickel foam. This anodic reaction lowers the electricity input of 317 mV toward the desired current density of 100 mA/cm², together with a highly selective benzonitrile product of more than 97%. More specifically, when coupling it with cathodic hydrogen evolution reaction (HER), the proposed HER||benzylamine-EODH configuration only requires a cell voltage of 1.47 V@100 mA/cm², exhibiting an energy-saving up to 17% relative to conventional water splitting, as well as the near unit selectivity toward cathodic H₂ and anodic benzonitrile products.     

Bimetallic cobalt-nickel coordination polymer electrocatalysts for enhancing oxygen evolution reaction

Coordination polymers（CPs） have great potential to be used in electrocatalysis owing to their designable compositions and structures. It is highly challenging to apply CPs as electrocatalysts for oxygen evolution reaction（OER） on account of insufficient catalytic efficiency and relatively poor stability of current electrocatalysts. Herein, through a mixed-metal strategy, one-dimensional Co_xNi_1-x-HIPA with dual active sites was synthesized and studied for OER electrocatalyst...     

Energy-efficient hydrogen production coupled with methanol oxidation using NiFe LDH@NiMo alloy heterostructure

The traditional electrochemical water splitting is extremely restricted by the sluggish kinetics of the anodic oxygen evolution reaction (OER). In this context, replacing OER with a more thermodynamic favorable oxidation reaction, such as methanol oxidation reaction (MOR), is an effective strategy to improve the hydrogen evolution reaction (HER) efficiency while still obtaining some valuable by-products. In this work, nickel-iron layered double-hydroxide [NiFe LDH]@NiMo alloy heterostructure is synthesized by electrodeposition process and its bi-functional electrocatalytic activities for both hydrogen evolution reaction (HER) and methanol oxidation reaction (MOR) are evaluated. For the HER, the catalyst exhibits low overpotential of 82.5 mV at 100 mA/cm², with a Tafel slope of 61 mV/dec as well as splendid long-term stability. For the MOR, the required potential decreases by 74 mV at 100 mA/cm² compared to oxygen evolution reaction (OER). Moreover, 97% process yields toward value-added formic acid (HCOOH) are obtained at the anode, with a faradaic efficiency of approximately 100% for HER at the cathode. The superior catalytic performance results from the synergic contribution of NiFe LDH and NiMo alloy. The formation of NiFe LDH@NiMo alloy heterostructure leads to the redistribution of electrons among nickel (Ni), iron (Fe) and molybdenum (Mo) elements. Therefore, the charge transfer process has been greatly promoted. This study provides a scalable energy saving strategy for hydrogen energy development.     

Ni3S2@NiFePx electrode with dual-anion-modulated layer for efficient and stable oxygen evolution

The rational construction of high-performance and stable electrocatalyst for oxygen evolution reaction (OER) is a prerequisite for efficient water electrolysis. Herein, we develop a broccoli-like Ni₃S₂@NiFeP_x (Ni₃S₂@NFP) catalyst on nickel foam (NF) via a sequential two-step layer-by-layer assembly electrodeposition method. X-ray diffraction, in situ Raman and Fourier-transform infrared spectra have mutually validated the element segregation and phase refusion during OER condition. The reconstruction of double layer Ni₃S₂@NFP facilitates the formation of the active (oxy)hydroxides, which is modulated by the dual anionic layer with mixed sulfate and phosphate ions. As a result, the obtained Ni₃S₂@NFP electrode exhibits low overpotential (329 mV) and long-term durability (∼500 h) for OER at current density of 500 mA/cm². Moreover, the self-supported Ni₃S₂@NFP can act as an efficient and durable anode in alkaline anion exchange membrane water electrolysis device (AEMWE). This work provides a facile and scaled-up strategy to construct self-supported electrocatalyst and emphasizes the crucial role of anions in pre-catalyst reconstruction and enhancing OER performance.     

Red Bean Pod Derived Heterostructure Carbon Decorated with Hollow Mixed Transition Metals as a Bifunctional Catalyst in Zn-Air Batteries

Design and synthesis of low-cost and efficient bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in Zn-air batteries are essential and challenging. We report a facile method to synthesize heterostructure carbon consisting of graphitic and amorphous carbon derived from the agricultural waste of red bean pods. The heterostructure carbon possesses a large surface area of 625.5 m² g⁻¹, showing ORR onset potential of 0.89 V vs. RHE and OER overpotential of 470 mV at 5 mA cm⁻². Introducing hollow FeCo nanoparticles and nitrogen dopant improves the bifunctional catalytic activity of the carbon, delivering ORR onset potential of 0.93 V vs. RHE and OER overpotential of 360 mV. Electron energy-loss spectroscopy (EELS) O K-edge map suggests the presence of localized oxygen on the FeCo nanoparticles, suggesting the oxidation of the nanoparticles. Zn-air battery with these carbon-based catalysts exhibits a peak power density as high as 116.2 mW cm⁻² and stable cycling performance over 210 discharge/charge cycles. This work contributes to the advancement of bifunctional oxygen electrocatalysts while converting agricultural waste into value-added material.     

Advanced Bifunctional Oxygen Reduction and Evolution Electrocatalyst Derived from Surface‐Mounted Metal–Organic Frameworks

Metal–organic frameworks (MOFs) and their derivatives are considered as promising catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which are important for many energy provision technologies, such as electrolyzers, fuel cells and some types of advanced batteries. In this work, a “strain modulation” approach has been applied through the use of surface‐mounted NiFe‐MOFs in order to design an advanced bifunctional ORR/OER electrocatalyst. The material exhibits an excellent OER activity in alkaline media, reaching an industrially relevant current density of 200 mA cm^?2 at an overpotential of only ≈210 mV. It demonstrates operational long‐term stability even at a high current density of 500 mA cm^?2 and exhibits the so far narrowest “overpotential window” ΔE_ORR‐OER of 0.69 V in 0.1 m KOH with a mass loading being two orders of magnitude lower than that of benchmark electrocatalysts.     

Metallic Co4N Porous Nanowire Arrays Activated by Surface Oxidation as Electrocatalysts for the Oxygen Evolution Reaction

Designing highly efficient electrocatalysts for oxygen evolution reaction (OER) plays a key role in the development of various renewable energy storage and conversion devices. In this work, we developed metallic Co₄N porous nanowire arrays directly grown on flexible substrates as highly active OER electrocatalysts for the first time. Benefiting from the collaborative advantages of metallic character, 1D porous nanowire arrays, and unique 3D electrode configuration, surface oxidation activated Co₄N porous nanowire arrays/carbon cloth achieved an extremely small overpotential of 257 mV at a current density of 10 mA cm⁻², and a low Tafel slope of 44 mV dec⁻¹ in an alkaline medium, which is the best OER performance among reported Co‐based electrocatalysts to date. Moreover, in‐depth mechanistic investigations demonstrate the active phases are the metallic Co₄N core inside with a thin cobalt oxides/hydroxides shell during the OER process. Our finding introduces a new concept to explore the design of high‐efficiency OER electrocatalysts.     

Folded nanosheet-like Co<Subscript>0.85</Subscript>Se array for overall water splitting

Active, stable, and earth-abundant bifunctional electrocatalyst for overall water splitting is pivotal to actualize large-scale water splitting via electrolysis. In this work, the hierarchical folded nanosheet-like Co_0.85Se array on Ni foam is constructed by liquid-phase chemical conversion with cobalt precursor nanorod array. It can serve as an efficient bifunctional electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolyte, with a current density of 10 mA cm^?2 at overpotential of 232 mV for OER and 129 mV for HER and Tafel slope of 78.9 mV dec^?1 for OER and 95.0 mV dec^?1 for HER, respectively. The two-electrode alkaline water electrolyzer utilizing this folded nanosheet-like Co_0.85Se array as both anode and cathode toward overall water splitting offered a current of 10 mA cm^?2 at a cell voltage of 1.60 V. This work explores an efficient and low-cost electrocatalyst for overall water splitting application in alkaline electrolytes.     

Efficient electrocatalytic oxygen evolution at ultra-high current densities over 3D Fe,N doped Ni(OH)2 nanosheets

Developing highly efficient nickel or iron based hydroxide electrocatalysts is primary essential but challenging for oxygen evolution reaction (OER) at ultra-high current densities. Herein, we developed a facile method to prepare nitrogen and iron doped nickel(II) hydroxide nanosheets on self-supported conductive nickel foam (denoted as Fe,N-Ni(OH)₂/NF) through ammonia hydrothermal and impregnation methods. Owing to the optimization of the electronic structure by nitrogen doping and the strong synergistic effect between Fe and Ni(OH)₂, the three-dimensional (3D) Fe,N-Ni(OH)₂/NF nanosheets delivered superior electrocatalytic OER performances in basic solution with low potentials of 1.57 V and 1.59 V under 500 mA/cm² and 1000 mA/cm² respectively and robust operation for 10 h with ignored activity decay, comparing well with the potentials of previously reported NiFe based electrocatalysts as well as the benchmark commercial Ir/C/NF. In-situ Raman spectroscopy revealed that the main active species were NiOOH during the OER process. The present results are expected to provide new insights into the study of OER process towards ultra-high current densities.     

Bifunctional Near-Neutral Electrolyte Enhances Oxygen Evolution Reaction

Performance of electrocatalytic reactions depends on not only the composition and structure of the active sites, but also their local environment, including the surrounding electrolyte. In this work, we demonstrate that BF₂(OH)₂⁻ anion is the key fluoroborate species formed in the mixed KBi/KF (KBi=potassium borate) electrolyte to enhance the rate of the oxygen evolution reaction (OER) at near-neutral pH. Through a combination of electrokinetic and in situ spectroscopic studies, we show that the mixed KBi/KF electrolyte promotes the OER via two pathways: 1) stabilizing the interfacial pH during the proton-producing reaction with its high buffering capacity; and 2) activating the interfacial water via strong hydrogen bonds with F-containing species. With the KBi/KF electrolyte, electrodeposited Co(OH)₂ is able to achieve 100 mA/cm² at 1.74 V, which is among the highest reported activities with earth-abundant electrocatalysts at near neutral conditions. These findings highlight the potential of leveraging electrolyte-engineering for improving the electrochemical performance of the OER.     

Electrodeposition at Highly Negative Potentials of an Iron-Cobalt Oxide Catalyst for Use in Electrochemical Water Splitting

Earth-abundant transition metal-based catalysts have been extensively investigated for their applicability in water electrolysers to enable overall water splitting to produce clean hydrogen and oxygen. In this study a Fe−Co based catalyst is electrodeposited in 30 seconds under vigorous hydrogen evolution conditions to produce a high surface area material that is active for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). This catalyst can achieve high current densities of 600 mAcm⁻² at an applied potential of 1.6 V (vs RHE) in 1 M NaOH with a Tafel slope value of 48 mV dec⁻¹ for the OER. In addition, the HER can be facilitated at current densities as high as 400 mA cm⁻² due to the large surface area of the material. The materials were found to be predominantly amorphous but did contain crystalline regions of CoFe₂O₄ which became more evident after the OER indicating interesting compositional and structural changes that occur to the catalyst after an electrocatalytic reaction. This rapid method of creating a bimetallic oxide electrode for both the HER and OER could possibly be adopted to other bimetallic oxide systems suitable for electrochemical water splitting.