Why shouldn’t double-layer capacitance (Cdl) be always trusted to justify Faradaic electrocatalytic activity differences?

The excellent performance of oxygen evolution reaction on stainless steel electrodes by halogen oxyacid salts etching

Development of low-cost, efficient, and stable electrocatalysts for oxygen evolution reaction (OER) is the key issue for a large-scale hydrogen production. Recently, in-situ corrosion of stainless steel seems to be a feasible technique to obtain an efficient OER electrode, while a wide variety of corrosive agents often lead to significant difference in catalytic performance. Herein, we synthesized Ni-Fe based nanomaterials with OER activity through a facile one-step hydrothermal etching method of stainless steel mesh, and investigated the influence of three halogen oxyacid salts (KClO3, KBrO3, KIO3) on water oxidation performance. It was found that the reduction product of oxyacid salts has the pitting effect on the stainless steel, which plays an important role in regulating the morphology and composition of the nanomaterials. The KBrO3-derived electrode shows optimal OER performance, giving the small overpotential of 228 and 270 mV at 10 and 100 mA cm-2 respectively, a low Tafel slope of 36.2 mV dec-1, as well as durable stability in the long-time electrolysis. This work builds an internal relationship between the corrosive agents and the OER performance of the as-prepared electrodes, providing promising strategies and research foundations for further improving the OER performance and optimizing the structure of stainless steel electrodes.

Active site engineering of intermetallic nanoparticles by the vapour-solid synthesis: carbon black supported nickel tellurides for hydrogen evolution

The development and design of catalysts have become a major pillar of latest research efforts to make sustainable forms of energy generation accessible. The production of green hydrogen by electrocatalytic water splitting is dealt as one of the most promising ways to enable decarbonization. To make the hydrogen evolution reaction through electrocatalytic water splitting usable on a large scale, the development of highly-active catalysts with long-term stability and simple producibility is required. Recently, nickel tellurides were found to be an interesting alternative to noble-metal materials. Previous publications dealt with individual nickel telluride species of certain compositions due to the lack of broadly applicable synthesis strategies. For the first time, in this work the preparation of carbon black supported nickel telluride nanoparticles and their catalytic performance for the electrocatalytic hydrogen evolution reaction in alkaline media is presented. The facile vapour-solid synthesis strategy enabled remarkable control over the crystal structure and composition, demonstrating interesting opportunities of active site engineering. Both single- and multi-phase samples containing the Ni-Te compounds Ni3Te2, NiTe, NiTe2-x & NiTe2 were prepared. Onset potentials and overpotentials of -0.145 V vs. RHE and 315 mV at 10 mA cm-2 respectively were achieved. Furthermore, it was found that the mass activity was dependent on the structure and composition of the nickel tellurides following the particular order: Ni3Te2 > NiTe > NiTe2-x > NiTe2.

α-Bi2Mo3O12: A Dual-Functional Material for Electrocatalytic Water Splitting and Supercapacitor Applications

This study explores the functionality of α-Bi2Mo3O12 (BMO) as an electrocatalyst for water splitting and its suitability for supercapacitor applications. BMO was synthesized by the solvothermal method and characterized in pre-calcination [BMO (BC)], post-calcination [BMO (AC)], and base-etched forms [BMO (BE)]. Structural analysis confirmed the formation of α-Bi2Mo3O12 with well-defined crystallographic planes. Electrochemical analysis revealed that BMO (AC) exhibited the lowest overpotential for hydrogen evolution reactions (HER) and BMO (BC) exhibited the lowest overpotential for oxygen evolution reactions (OER), indicating its superior electrocatalytic activity. The Tafel slope and electrochemical impedance spectroscopy results confirmed the superior kinetics and charge transfer properties of BMO material. Furthermore, BMO samples demonstrated excellent stability during prolonged chronoamperometry (CA) testing for 12 h. For supercapacitor performances, the BMO (BE) exhibits a superior specific capacitance value of 398 F/g at 2.0 A/g. Thus, the BMO material delivers prominent electrocatalytic activity as well as supercapacitor performance. Overall, this study demonstrates the potentiality of α-Bi2Mo3O12 in different forms as a dual-functional material for efficient energy storage and conversion.

Nanocomposites based on Cu2O coated silver nanowire networks for high-performance oxygen evolution reaction

The development of highly active, low-cost, and robust electrocatalysts for the oxygen evolution reaction (OER) is a crucial endeavor for the clean and economically viable production of hydrogen via electrochemical water splitting. Herein, cuprous oxide (Cu2O) thin films are deposited on silver nanowire (AgNW) networks by atmospheric-pressure spatial atomic layer deposition (AP-SALD). AgNW@Cu2O nanocomposites supported on conductive copper electrodes exhibited superior OER activity as compared to bare copper substrate and bare AgNWs. Moreover, a relationship between Cu2O thickness and OER activity was established. Notably, the most effective catalyst (AgNW@50nm-thick Cu2O) demonstrated very high OER activity with a low overpotential of 409 mV to deliver a current density of 10 mA cm-2 (η 10), a Tafel slope of 47 mV dec-1, a turnover frequency (TOF) of 4.2 s-1 at 350 mV, and good durability in alkaline media (1 M KOH). This highlights the potential of AgNWs as a powerful platform for the formation of highly efficient copper oxide catalysts towards OER. This work provides a foundation for the development of nanostructured Cu-based electrocatalysts for future clean energy conversion and storage systems.

Study on Water Splitting of the 214-Type Perovskite Oxides LnSrCoO4 (Ln = La, Pr, Sm, Eu, and Ga)

We present a study on the electrocatalysis of 214-type perovskite oxides LnSrCoO4 (Ln = La, Pr, Sm, Eu, and Ga) with semiconducting-like behavior synthesized using the sol-gel method. Among these five catalysts, PrSrCoO4 exhibits the optimal electrochemical performance in both the oxygen evolution reaction and the hydrogen evolution reaction, mainly due to its larger electrical conductivity, mass activity, and turnover frequency. Importantly, the weak dependency of LSV curves in a KOH solution with different pH values, revealing the adsorbate evolving mechanism in PrSrCoO4, and the density functional theory (DFT) calculations indicate that PrSrCoO4 has a smaller Gibbs free energy and a higher density of states near the Fermi level, which accelerates the electrochemical water splitting. The mutual substitution of different rare-earth elements will change the unit-cell parameters, regulate the electronic states of catalytic active site Co ions, and further affect their catalytic performance. Furthermore, the magnetic results indicate strong spin-orbit coupling in the electroactive sites of Co ions in SmSrCoO4 and EuSrCoO4, whereas the magnetic moments of Co ions in the other three catalysts mainly arise from the spin itself. Our experimental results expand the electrochemical applications of 214-type perovskite oxides and provide a good platform for a deeper understanding of their catalytic mechanisms.

Porous tremella-like NiMoP/CoP network electrodes as an efficient electrocatalyst

The design of efficient, stable and cost-effective electrocatalysts for the hydrogen evolution reaction holds substantial significance in water electrolysis, but it remains challenging. Tremella-like nickel-molybdenum bimetal phosphide encapsulated cobalt phosphide (NiMoP/CoP) with hierarchical architectures has been effectively synthesized on nickel foam (NF) via a straightforward hydrothermal followed by low-temperature phosphating method. Based on the unique structural benefits, it significantly increases the number of redox active centers, enhances the electrical conductivity of materials, and diminishes the ion diffusion path lengths, thereby promoting efficient electrolyte penetration and reducing the inherent resistance. The as-obtained NiMoP/CoP/NF electrocatalyst exhibited remarkable catalytic activity with an ultralow overpotential of 38 mV (10 mA cm-2) and low Tafel slope of 83 mV dec-1. The straightforward synthesis process and exceptional electrocatalytic properties of NiMoP/CoP/NF demonstrate great potential for the HER to replace the precious metal catalyst.

Hollow Starlike Ag/CoMo-LDH Heterojunction with a Tunable d-Band Center for Boosting Oxygen Evolution Reaction Electrocatalysis

It is a challenging task to utilize efficient electrocatalytic metal hydroxide-based materials for the oxygen evolution reaction (OER) in order to produce clean hydrogen energy through water splitting, primarily due to the restricted availability of active sites and the undesirably high adsorption energies of oxygenated species. To address these challenges simultaneously, we intentionally engineer a hollow star-shaped Ag/CoMo-LDH heterostructure as a highly efficient electrocatalytic system. This design incorporates a considerable number of heterointerfaces between evenly dispersed Ag nanoparticles and CoMo-LDH nanosheets. The heterojunction materials have been prepared using self-assembly, in situ transformation, and spontaneous redox processes. The nanosheet-integrated hollow architecture can prevent active entities from agglomeration and facilitate mass transportation, enabling the constant exposure of active sites. Specifically, the powerful electronic interaction within the heterojunction can successfully regulate the Co3+/Co2+ ratio and the d-band center, resulting in rational optimization of the adsorption and desorption of the intermediates on the site. Benefiting from its well-defined multifunctional structures, the Ag0.4/CoMo-LDH with optimal Ag loading exhibits impressive OER activity, the overpotential being 290 mV to reach a 10 mA cm-2 current density. The present study sheds some new insights into the electron structure modulation of hollow heterostructures toward rationally designing electrocatalytic materials for the OER.

Enhanced CO Functionality on Carbon Papers Ensures Lowering Nucleation Delay of ALD for Ru towards Unprecedented Alkaline HER Activity

The success in lowering the nucleation delay for Atomic Layer Deposition (ALD) of Ru on carbon surfaces is mitigated by constructive pretreatments resulting enhancement of CO functionality. Treatment of the carbon papers (CP) allowed Ru species deposition for minimum number of ALD cycles (25 cycles) with good conformality. The development of electrocatalysts from single atoms to nanoparticles (NPs) on conductive supports with low metal loadings, thus improving performance, is essential in electrocatalysis. For alkaline hydrogen evolution reaction, ALD decorated CPs with Ru exhibit low onset potentials of ≈4.7 mV versus reversable hydrogen electrode (RHE) (at 10 mA cm-2 ) and a high turnover frequency of 1.92 H2 s-1 at 30 mV versus RHE. The Ru decorated CPs show comparable to higher catalytic activity than of Platinum (Pt) decorated CP also developed by ALD. The current representation of unfamiliar catalytic activities of Ru active centers developed by ALD, pave a bright and sustainable path for energy conversion reactions.

Impedimetric nano-collision Escherichia coli analysis based on Silver-Gold bimetallic nanoparticles

An impedimetric detection of E. coli was developed using chemically synthesised bimetallic Ag-Au (1:2) nanoparticles (NPs). The UV-visible spectra of the NPs had absorption bands at 470 and 580 nm for Ag NPs and Au NPs, respectively. In the presence of E. coli, a negative potential shift and a blue shift was observed in the voltammograms and spectra respectively. The complex formed had an oxidation potential at + 0.95 V. Technique choice was based on sensitivity comparison of Differential pulse voltammetry, cyclic voltammetry and impedance spectroscopy in 0.1 M PBS with Impedance being the best choice. Optimum sensing conditions of the NPs-E. coli complex for NPs concentration, incubation period, method modulation amplitude and applied potential were 5 mM, 20 min, 10 mV and + 0.5 V, respectively. The sensor's linearity range, lower limits of detection and quantification were found to be 10¹-10⁷, 1.88 × 10¹, 2.34 × 10² cells/mL, respectively. The sensor's applicability was validated by repeatability, stability and selectivity studies showing minimum changes in signal. Potential usage of the sensor in real samples was demonstrated by standard addition analysis of sea and River water samples as well as recovery of spiked water and fruit juices with acceptable % RSD < 2%.

CeO2/CuO/NiO hybrid nanostructures loaded on N-doped reduced graphene oxide nanosheets as an efficient electrocatalyst for water oxidation and non-enzymatic glucose detection

In this work, the three-component heterostructure of CeO₂/CuO/NiO was synthesized by a co-precipitation procedure and heating at a temperature of 750 °C. Then, CeO₂/CuO/NiO nanoparticles were successfully supported on N-doped reduced graphene oxide (N-rGO) by a hydrothermal method. The obtained nanomaterials were used as effective electrocatalysts for the oxygen evolution reaction and glucose sensing in an alkaline medium. The results indicated that when CeO₂/CuO/NiO is anchored on N-rGO nanosheets, active catalytic sites increase. On the other hand, N-doped rGO enhances electrical conductivity and electron transfer for water or glucose oxidation. CeO₂/CuO/NiO@N-rGO has a large electrochemically active surface area and more active catalytic positions, and thus exhibits high activity for the OER with a low overpotential of 290 mV, a suitable Tafel slope of 110 mV dec^-1, and superior stability and durability for at least 10 hours. CeO₂/CuO/NiO@N-rGO can also detect glucose with a high sensitivity of 912.7 μA mM^-1 cm^-2, a low detection limit of 0.053 μM, a wide linear range between 0.001 and 24 mM, and a short response time of about 2.9 s. Moreover, the high selectivity and stability of this electrode for glucose sensing show its potential for clinical applications.

NiMo solid-solution alloy porous nanofiber as outstanding hydrogen evolution electrocatalyst

Developing a high-efficiency hydrogen evolution reaction (HER) electrocatalyst for the large-scale production of hydrogen is essential but challenging. In this study, we used NiMo solid-solution alloy porous nanofibers to develop a robust HER electrocatalyst through electrospinning, oxidization, and high-temperature reduction treatment. In 1 M KOH electrolyte, the fabricated NiMo solid-solution alloy porous nanofibers exhibited higher HER activity than Ni nanofibers, which required a low overpotential of 69, 208, and 300 mV at 100, 500, and 1000 mA cm^-2, respectively, and had outstanding durability at 100 mA cm^-2 over 60 h. We developed a promising candidate for a high-efficiency HER electrocatalyst, and our findings provided valuable information for fabricating highly robust alloy-based electrocatalysts.

Novel Strain Engineering Combined with a Microscopic Pore Synergistic Modulated Strategy for Designing Lattice Tensile-Strained Porous V2C-MXene for High-Performance Overall Water Splitting

Transition metal carbon/nitride (MXene) holds immense potential as an innovative electrocatalyst for enhancing the overall water splitting properties. Nevertheless, the re-stacking nature induced by van der Waals force remains a significant challenge. In this work, the lattice tensile-strained porous V₂C-MXene (named as TS₍₂₄₎-P₍₅₀₎-V₂C) is successfully constructed via the rapid spray freezing method and the following hydrothermal treatment. Besides, the influence of lattice strain degree and microscopic pores on the catalytic ability is reviewed and explored systematically. The lattice tensile strain within V₂C-MXene could widen the interlayer spacing and accelerate the ion transfer. The microscopic pores could change the ion transmission path and shorten the migration distance. As a consequence, the obtained TS₍₂₄₎-P₍₅₀₎-V₂C shows extraordinary hydrogen evolution reaction and oxygen evolution reaction activity with the overpotential of 154 and 269 mV, respectively, at the current density of 10 mA/cm², which is quite remarkable compared to the MXene-based electrocatalysts. Moreover, the overall water splitting device assembled using TS₍₂₄₎-P₍₅₀₎-V₂C as both anode and cathode demonstrates a low cell voltage requirement of 1.57 V to obtain 10 mA/cm². Overall, the implementation of this work could offer an exciting avenue to overcome the re-stacking issue of V₂C-MXene, affording a high-efficiency electrocatalyst with superior catalytic activity and desirable reaction kinetics.

Ru doping boosts electrocatalytic water splitting

Heteroatom doping plays a crucial role in improving the electrocatalytic performance of catalysts towards water splitting. Owing to the existence of Ru-O moieties, Ru is thus emerging as an ideal dopant for promoting the electrocatalytic performance for water splitting by modifying the electronic structure, introducing extra active sites, improving electronic conductivity, and inducing a strong synergistic effect. Benefitting from these advantages, Ru-doped nanomaterials have been widely investigated and employed as advanced electrocatalysts for water splitting, and many excellent Ru-doped electrocatalysts have been successfully developed. In an effort to obtain a better understanding of the influence of Ru doping on the electrocatalytic water splitting performance of nanocatalysts, we herein summarize the recent progress of Ru-doped electrocatalysts by focusing on the synthesis strategies and advantageous merits. Applications of these new materials in water electrolysis technology are also discussed with emphasis on future directions in this active field of research.

Flower-like Co3Ni1B nanosheets based on reduced graphene oxide (rGO) as an efficient electrocatalyst for the oxygen evolution reaction

Flower-like Co3Ni1B nanosheets based on a reduced graphene oxide electrocatalyst exhibit a better OER performance than commercial RuO2.