Oxygen Reduction Reaction Onset Potential Research Articles

Co-NC catalyst with rich coordinated nitrogen and hierarchical porous structure for oxygen reduction reaction

Cobalt nitrogen-doped carbon (Co-NC) catalysts are synthesized for oxygen reduction reaction (ORR) via the pyrolysis of zinc-mediated and SiO2-templated 2,6-diaminopyridine (DAP) composites. The resulting Co-NC(Zn12-SiO2[20])-900 demonstrates exceptional ORR activities, with half-wave and onset potentials of 0.835 V and 0.875 V, respectively, which is similar to Pt/C catalyst. In long-term durability test, the Co-NC(Zn12-SiO2[20])-900 catalyst exhibits a negligible E1/2 shift, and in methanol tolerance tests, it displays significantly better performance than commercial Pt/C catalyst. The superior performance can be attributed to the hierarchical porous structure, dense and highly accessible Co-N4 and graphitic nitrogen (g-N) sites. The high content of Co-N4 and g-N sites enhances 3d-orbital filling and reduces the Co centers' on-site magnetic moment, as calculated by density functional theory. This may lead to a decrease in the energy barrier of the rate-determining step (RDS), which in turn enhances the intrinsic activity of the ORR.

Dimetallic praseodymium-cobalt carbon nanotubes as highly efficient electrocatalyst for oxygen reduction reaction

In this study, six bimetallic rare earth (RE = La, Ce, Pr, Nd, Sm, Eu) cobalt nitrogen doped carbon nanotubes (RECo-NCNTs) were synthesized with g-C3N4 derivative method. These RECo-NCNTs were characterized by SEM, BET, XPS, XRD and Raman. In addition, their catalytic performances for oxygen reduction reaction (ORR) had also been tested. The introduction of rare earths did not destroy the structure of nanotubes but apparently change their ORR performances. The PrCo-NCNTs showed the significant improvement in catalytic ability for ORR (onset potential of 0.95 V and half-wave potential of 0.79 V), which is very close to that of commercial 20 % Pt/C. Moreover, PrCo-NCNTs exhibits an excellent catalytic stability (no activity decay after 10000st cycles) and an outstanding methanol toxic tolerance. Assembled in metal–air batteries (Zn-air, Al-air and Mg-air), the PrCo-NCNTs electrode also presents high power densities and discharge voltages.

Deciphering the linear relationship in the activity of the oxygen reduction reaction on Pt electrodes: A decisive role of adsorbates

Despite substantial efforts in developing high-performance catalysts for the oxygen reduction reaction (ORR), the persistent challenge lies in the high onset overpotential of the ORR, and the effect of the electrolyte solution cannot be ignored. Consequently, we have systematically investigated the impact of adsorbate species and concentration, as well as solution pH, on the ORR activity on Pt(111) and Pt(poly) electrodes. The results all tend to establish a linear quantitative relationship between the onset potential for ORR and the adsorption equilibrium potential of the adsorbate. This finding indicates the decisive role of adsorbates in the onset potential for ORR, suggesting that the adsorption potential of adsorbates can serve as an intuitive criterion for ORR activity. Additional support for this conclusion is derived from experimental results obtained from the oxygen evolution reaction on Pt(poly) with different adsorbate species and from the hydrogen evolution reaction on Pt(111) with iodine adsorption. We further propose both an empirical equation for the onset potential for ORR and the concept of a potential-regulated adsorbate shielding effect to elucidate the influence of adsorbates on ORR activity. This study provides new insights into the high onset overpotential of the ORR and offers potential strategies for predicting and enhancing ORR activity in the future.

Organic hybrid of cobalt phthalocyanine embedded graphene as an efficient catalyst for oxygen reduction reaction

The widespread practical applications of the fuel cells are dependent on the rational development of state-of-the-art easily synthesizable or earth-abundant catalysts for oxygen reduction reaction (ORR). This work demonstrates the utilization of cobalt phthalocyanine polymer (pCoPc) encased graphene (Gr) layer with an extensive π-π interaction as a proficient and non-precious electrocatalyst for ORR. The synthesized material is characterized by UV–vis, IR, Mass, NMR, SEM, TEM and XPS techniques. The fabricated Gr-pCoPc catalyst exhibited significant enhancement in the ORR performance which is comparable to the benchmark Pt/C catalyst with a decent durability in alkaline media. More importantly, the ORR onset potential at Gr-pCoPc shifted towards the positive potential by 10 mV compared to the Pt/C catalyst. The enhancement observed in the ORR performance and stability of the Gr-pCoPc catalyst could be attributed to the combined impact created by the outstanding electronic and conductive attributes of graphene, along with the π-stacking interactions inherent in pCoPc. In comparison to prior catalysts in literature and Pt/C, Gr-pCoPc displayed a notably lower Tafel slope of 64 mV dec-1 and larger double layer capacitance, Cdl value of 9.5 mF cm−2. The RDE experiments indicated that the hybrid composite of Gr-pCoPc facilitated an effective 4-electron pathway during ORR. Gr-pCoPc catalyst is highly durable towards ORR and it retained > 92.5 % of its initial ORR activity even after 5000 repeated cycles.

Pyrolysis-free cobalt porphyrin coordination polymer as electrocatalyst for Zn-air batteries and water splitting

The development of high-performance and stable trifunctional electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) plays key role in the practical application of renewable energy systems. Herein, we report a pyrolysis-free synthesis of a CoNC based porphyrin cobalt coordination polymer electrocatalyst by using 5,10,15, 20-tetrad-[4′-(terpyridinyl) phenyl] porphyrin and cobalt bivalent ions. The polymer exhibits pronounced trifunctionality at a low ORR onset potential of 0.87 V vs. RHE, and an overpotentials of 378 and 210 mV at 10 mA cm−2 for the OER and HER with substantial stability in alkaline media. In the constructed aqueous Zn-air battery, it displays satisfied specific capacity of 723 mAh g−1 and appreciable stability for 85 h. Density functional theory computations reveal that TTBPP-Co exhibits excellent donor–acceptor characteristics with HOMO-LUMO band gap of 1.87 eV. This work provides a new design of metal porphyrin coordination polymers as efficient trifunctional electrocatalysts for clean energy applications.

Exploring the Impact of DAHP Impregnation on Activated Carbon Fibers for Efficient Charge Storage and Selective O2 Reduction to Peroxide

Understanding the properties and behavior of carbon materials is of paramount importance in the pursuit of sustainable energy solutions and technological advancements. As versatile and abundant resources, carbon materials play a central role in various energy conversion and storage applications, making them essential components in the transition toward a greener and more efficient future. This study explores the impact of diammonium hydrogen phosphate (DAHP) impregnation on activated carbon fibers (ACFs) for efficient energy storage and conversion applications. The viscose fibers were impregnated with varying DAHP concentrations, followed by carbonization and activation processes. The capacitance measurements were conducted in 6 mol dm−3 KOH, 0.5 mol dm−3 H2SO4, and 2 mol dm−3 KNO3 solutions, while the oxygen reduction reaction (ORR) measurements were performed in O2-saturated 0.1 mol dm−3 KOH solution. We find that the presented materials display specific capacitances up to 160 F g−1 when the DAHP concentration is in the range of 1.0 to 2.5%. Moreover, for the samples with lower DAHP concentrations, highly selective O2 reduction to peroxide was achieved while maintaining low ORR onset potentials. Thus, by impregnating viscose fibers with DAHP, it is possible to tune their electrochemical properties while increasing the yield, enabling the more sustainable and energy-efficient synthesis of advanced materials for energy conversion applications.

Directly assembling initial metal–organic framework and covalent organic polymer toward bifunctional oxygen electrocatalysts for Zn-air flow battery

Developing highly efficient bifunctional oxygen electrocatalysts is important but still remains a challenge for Zn-air flow battery. Metal-organic frameworks (MOFs) and covalent organic polymers (COPs) materials have emerged as promising alternatives to the benchmark precious metal electrocatalysts due to their designable and controllable structures at the atomic level. However, their catalytic performances are limited by the conductivity and catalytic activity using initial materials. Moreover, these materials are generally developed either as single oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) electrocatalysts. Herein, we utilize the π-π stacking effect to directly assemble initial nanosheet FeNi-MOF and iron phthalocyanine rich COP hybrid materials toward the highly efficient bifunctional electrocatalysts via pyrolysis-free strategy. The carbon black is added to the composite as support to limit the stacking of composites and increase the conductivity. The obtained catalyst, named as NSFeNi@COPFe-C, exhibits superior catalytic performance with an ORR onset potential of 0.99 V (vs. reversible hydrogen electrode: RHE), half-wave potential of 0.9 V (vs. RHE), and the OER potential of 1.65 V at 10 mA cm−2 in alkaline electrolyte. The assembled zinc-air flow battery with NSFeNi@COPFe-C as the bifunctional oxygen electrocatalyst shows a discharge power up to 115 mW cm−2 and a long-term stability.

Theory‐guided Design of Atomically Dispersed Dual‐Metal Catalysts for Superior Oxygen Reduction Reaction Activity

AbstractThe widespread application of electrochemical energy conversion devices, such as proton exchange membrane fuel cells, is hindered by the kinetically sluggish oxygen reduction reaction (ORR) at the cathode. Transition‐metal and nitrogen codoped carbon materials (TM−N−C) are among the most promising catalysts to solve this problem. Particularly, dual‐metal TM−N−C have already displayed excellent performance. However, further knowledge on the reaction mechanism and the structure−activity relationship is still required. In this study, we established three dual‐metal TM−N−C models (FeMn−N−C, FeCo−N−C, and FeNi−N−C) to investigate the electronic interaction between the metallic sites and their corresponding adsorption strength for oxygenated intermediates in ORR electrocatalysis. Then, using density functional theory calculations, we determined that the ORR activity of the dual‐metal TM−N−C models followed the order of FeCo−N−C > FeNi−N−C > FeMn−N−C. We confirmed the theoretically predicted activity by synthesizing atomically dispersed FeMn−N−C, FeCo−N−C, and FeNi−N−C catalysts using metal‐organic framework precursors, among which FeCo−N−C showed the best results in terms of ORR onset potential and half‐wave potential (0.92 and 0.81 V vs. the reference hydrogen electrode in 0.1 M HClO4, respectively.). The results demonstrate the feasibility of the theory‐guided rational design of efficient dual‐metal catalysts for ORR electrocatalysis.

Co(II) Porphyrin-MWCNT Nanoconjugate as an Efficient and Durable Electrocatalyst for Oxygen Reduction Reaction.

Recently, researchers are seeking alternatives to replace Pt-based oxygen reduction reaction (ORR) catalysts used in fuel cells due to their high cost and certain stability and selectivity issues. For this purpose, we have synthesized a nanoconjugate, cobalt(II) porphyrin (5,10,15-triphenyl-20-(4-aminophenyl)porphyrinatocobalt(II), CoTPP-NH2) covalently attached to the acid-functionalized multiwalled carbon nanotubes and characterized by various techniques including UV-vis spectroscopy, FTIR, TGA, FESEM, TEM, and Raman spectroscopy. The oxygen reduction performance of the nanoconjugate is checked in basic medium. The ORR onset potential of the nanoconjugate-modified electrode is nearly the same as that of the state-of-the-art platinum-carbon electrode and stable for more than 3000 CV cycles with a 20 mV difference in the onset potential before and after the 3000 CV cycles. The above extrapolations reveal that the nanoconjugate has efficient performance for the ORR in basic medium.

Activity promotion of bifunctional catalysis by Se-doping and the application in rechargeable zinc-air batteries

Efficient bifunctional catalysts capable of catalyzing both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are required for the air electrode. Herein, the Se-doped FeNiP nanoparticles/N, P dual-doped carbon composite catalysts (FeNiP/SeNPC-2) were developed. The Se elements combine with various elements to form a compact heterogeneous material. At the same time, the Se-doping have modulated the crystal and surface structures, which have improved the catalytic activities of ORR and OER. The overpotential of OER was significantly negatively shifted, accompanied by a significant positive shift of the onset potential of ORR. FeNiP/SeNPC-2 has displayed an overpotential of 269 mV at the current density of 10 mA cm−2 for OER, and with a high half-wave potential (0.86 V) of ORR. The liquid zinc-air battery assembled using FeNiP/SeNPC-2 exhibited a power density of 171 mW cm−2 and stably charge-discharge cycled for 150 h. The solid-state zinc-air battery exhibited a power density of 88 mW cm−2 and stably charge-discharge cycled for 42 h. Subsequently, the solid-state zinc-air batteries of cylindrical hollow design are integrated as modules for driving devices.

FeCo alloy encapsulated in N-doped carbon shell for efficient oxygen reduction reaction

This work reports the synthesis of FeCo alloy encapsulated in N-doped carbon shell for efficient oxygen reduction reaction (ORR). The FeCoNC-0.3compound were synthesized by high temperature pyrolysis of ZIF-L with the assistance of different Fe salts (i.e., FeCl3·6H2O, FeSO4·7H2O, K3Fe(CN)6, Fe(NH4)2·(SO4)2·6H2O and (NH4)3·Fe(C2O4)3·3H2O). With the presence of FeCl3·6H2O, FeSO4·7H2O, Fe(NH4)2·(SO4)2·6H2O and (NH4)3·Fe(C2O4)3·3H2O during the pyrolysis process, FeCo alloys are formed and more nitrogen elements are remained after high temperature pyrolysis compared with that in CoNC derived from pure ZIF-L. Differently, the introduction of K3Fe(CN)6 cannot lead to the generation of FeCo alloy and less nitrogen elements are remained after high temperature pyrolysis in comparison with that in CoNC. Linear relationship between the ORR onset potential and the ID/IG value of the FeCoNC-0.3compound catalysts are observed. Besides, the onset potential also increases linearly with the increase of the total content of pyridinic-N + graphitic-N + Fe(Co)-Nx. These results suggest that high content of carbon defects and high content of pyridinic-N, graphitic-N and Fe(Co)-Nx are beneficial for the improvement of the catalytic activities of the FeCoNC-0.3compound catalysts. Among all the as-prepared samples, FeCoNC-0.3FeCl3 demonstrates the highest catalytic activity towards ORR due to its unique core–shell structure with a carbon layer as the shell and FeCo alloy as the core, hierarchical channels, large pore volume, high content of carbon defects and high total content of pyridine-N, graphite-N and Fe(Co)-Nx. FeCoNC-0.3FeCl3 displays an onset potential of 0.97 V and half-wave potential of 0.82 V, which are comparable to the commercial Pt/C (onset potential of 1.05 V, half-wave potential of 0.86 V). Moreover, FeCoNC-0.3FeCl3 demonstrates much higher durability and methanol tolerance compared with Pt/C. Zn-air battery with FeCoNC-0.3FeCl3 as the cathode catalyst demonstrates maximum power density of 105 mW cm−2, which is close to that with Pt/C as the cathode catalyst (127 mW cm−2).

Potential-Dependent Oxygen Reduction on FeN4 under Explicit Solvation Environment

Atomically dispersed FeN4 catalysts have been considered promising materials to replace the expensive Pt-based catalysts for oxygen reduction reaction (ORR), the development of which requires a fundamental understanding of the mechanism underlying their catalytic activity. Herein, we simulate the potential-dependent ORR process via density functional theory calculations and find that the O2 adsorption step becomes the rate-determining step (RDS) at slightly higher applied voltages and the onset potential is 0.8 V, which is because the substrate (*) and *OH intermediates are stabilized at constant potential states (CPS), yet the O2 adsorption becomes thermodynamically unfavorable compared to that at neutral charge states (NCS). The weakened O2 adsorption is attributed to the adjusted Fermi level at CPS that broadens the density of state distribution of the Fe 3d orbital. The determined RDS and the onset potential of ORR over FeN4 by performing potential-dependent simulations agree well with experimental findings, which improves the understanding of the ORR catalytic activity at applied potentials.

MOF-Derived CoNi Nanoalloy Particles Encapsulated in Nitrogen-Doped Carbon as Superdurable Bifunctional Oxygen Electrocatalyst

Carbon-encapsulated transition metal catalysts have caught the interest of researchers in the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) due to their distinctive architectures and highly tunable electronic structures. In this work, we synthesized N-doped carbon encapsulated with CoNi nanoalloy particles (CoNi@NC) as the electrocatalysts. The metal-organic skeleton ZIF-67 nanocubes were first synthesized, and then Ni2+ ions were inserted to generate CoNi-ZIF precursors by a simple ion-exchange route, which was followed by pyrolysis and with urea for the introduction of nitrogen (N) at a low temperature to synthesize CoNi@NC composites. The results reveal that ZIF-67 pyrolysis can dope more N atoms in the carbon skeleton and that the pyrolysis temperature influences the ORR and OER performances. The sample prepared by CoNi@NC pyrolysis at 650 °C has a high N content (9.70%) and a large specific surface area (167 m2 g-1), with a positive ORR onset potential (Eonset) of 0.89 V vs. RHE and half-wave potential (E1/2) of 0.81 V vs. RHE in 0.1 M KOH, and the overpotential of the OER measured in 1 M KOH was only 286 mV at 10 mA cm-2. The highly efficient bifunctional ORR/OER electrocatalysts synthesized by this method can offer some insights into the design and synthesis of complex metal-organic frameworks (MOFs) hybrid structures and their derivatives as functional materials in energy storage.

Highly active CoFe alloy nanoparticles encapsulated in N-doped carbon nanostructures for oxygen reduction reaction in both alkaline and acidic media

We report our facile and efficient approach for synthesizing Co-Fe alloy based oxygen reduction reaction (ORR) catalysts, in which alloy nanoparticles are encapsulated in nitrogen-doped carbon nanostructures. The catalysts with high hierarchical porosities are fabricated at an appropriate temperature of 775 °C without a further acid leaching treatment after pyrolysis due to the use of ZnO nanoparticles as auto-removable templates. Co/Fe atomic ratio is found to greatly influence the ORR catalytic activity. The catalyst with Co/Fe = 1 exhibits the best catalytic performance by showing an ORR onset potential of 0.99 V and a half-wave potential of 0.87 V (vs. RHE) in 0.1 M KOH, as well as 0.98 V and 0.83 V (vs. RHE) in 0.5 M H2SO4, better than or approaching the performance presented by a commercial 28.6 wt% Pt/C catalyst. The Zn-air battery using the synthesized CoFe@N-C catalyst delivers a higher power density at ambient conditions by air-breathing than the one using the 28.6 wt% Pt/C catalyst. Relatively higher atomic concentrations of both Fe and Co as well as more graphitic nitrogen in the surface of CoFe@N-C detected by X-ray photoelectron spectroscopy (XPS) may account for its excellent ORR catalytic activities both in alkaline and acidic environments.

Effect of fine structure and pore volume in the Marimo-like carbon cathode material on the oxygen reduction reaction for the polymer electrolyte fuel cell

We measured the rotating ring-disk electrode (RRDE) voltammetry curves of a Pt catalyst supported on Marimo-like carbon (MC) to clarify the effect of carbon nanofilaments (CNFs) morphology and fine structures consisting of MC cathode material on the oxygen reduction reaction (ORR) activity for Polymer electrolyte fuel cells. The specific surface area and pore volume of MCs are influenced by their morphology and fine structures. MCs grown with Ni–Cu bimetal catalyst (represented as Ni80Cu20MC), having an octopus-like morphology, yielded four times larger total pore volume than that measured from the MC grown with Ni catalyst (Ni100MC). In the case of Ni80Cu20MC, coin-stacked graphenes perpendicular to the filament axis formed CNFs. Ni100MC consists of cup-stacked CNFs. The difference in the graphene stacked fine structure resulted in a different number of graphene edges covering the CNF surface; however, both supported Pt particle sizes and their distributions were similar. Linear sweep voltammetry with a RRDE revealed that the Pt/Ni80Cu20MC ORR onset potential was higher than that observed from the Pt/Ni100MC. This value is suggested to be correlates with the ORR activity. The origin of the ORR difference was discussed on the basis of the structural difference in the MCs.

N-Doped Hollow Carbon Sphere and Polyhedral Carbon Composite Supported Pt/Fe Nanoparticles as Highly Efficient Cathodic Catalysts of Proton-Exchange Membrane Fuel Cells

With the growing energy crisis, people urgently need green energy sources to replace fossil ones. As a zero-emission clean energy source, the proton-exchange membrane fuel cell (PEMFC) has received growing attention from researchers due to its broad practical application. However, so far only noble metal Pt can be used as a mature cathodic catalyst for PEMFC to effectively promote the slow kinetic process of the oxygen reduction reaction (ORR). Herein, a low Pt-loading carbon-based catalyst (pCN@NHCS-Fe/Pt-280) with hollow carbon spheres (HCSs), metal–organic frameworks (MOFs), and carbon nanotubes (CNTs) structure was synthesized by the thermal reduction of platinum acetylacetonate and pCN@NHCS-Fe. Compared with the benchmark Pt/C catalyst, pCN@NHCS-Fe/Pt-280 presents low cost, and its ORR onset potential (Eonset = 0.971 VRHE) and half-wave potential (E1/2 = 0.883 VRHE) in acidic media are comparable to those of 40% Pt/C (Eonset = 0.965 VRHE, E1/2 = 0.883 VRHE). In the durability test for ORR, its current retention percentage (92.3%) is still higher than 40% Pt/C (86.7%) after 10 000 s of the constant potential test, and its cyclic voltammetry (CV) and linear scan voltammetry (LSV) profiles after 500 cycles exhibit outstanding stability. Moreover, pCN@NHCS-Fe/Pt-280 quickly recovers to 79.1% of the initial value after adding methanol, while 40% Pt/C can recover only to 72.3%, indicating a superior ability in antialcohol oxidation. In addition, the maximum power density of pCN@NHCS-Fe/Pt-280 (518.7 mW cm–2) as the cathode catalyst of PEMFC in the H2–air cell test is also higher than that of Pt/C (515.3 mW cm–2), while its power density is lower than that of Pt/C in the H2–O2 cell test at different pressures due to the high-temperature influence at high current densities. This work provides a valuable idea for the design of multistructured (HCSs, MOFs, CNTs, etc.) electrocatalysts and a feasible strategy for the development of low-Pt-loaded ORR catalysts.

Carboxyl induced ultrahigh defects and boron/nitrogen active centers in cobalt-embedded hierarchically porous carbon nanofibers: The stable oxygen reduction reaction catalysis in acid

Transition metal-nitrogen-carbon (MNC) type catalysts have been considered a promising alternative to noble metals for oxygen reduction reaction (ORR) electrocatalysis. Nevertheless, poor stabilities of MNC catalysts in acidic solutions limit their commercialization. In this study, we design and synthesize novel three-dimensional (3D) cobalt (Co) nanoparticles encapsulated in ultrahigh content of boron (B) and nitrogen (N) -doped hierarchically porous carbon nanofibers (denoted as Co@BN-PCNFs) by carbonizing the 3D acetic acid/cobalt nitrate/4-hydroxybenzeneboronic acid/polyvinylpyrrolidone precursor networks woven using electrospinning method under a nitrogen atmosphere. The optimal Co@BN-PCNFs-900 catalyst has abundant micro/mesopores and numerous topological defects and exhibits the largest surface area. Under the synergistic effect of oxygen-containing acetic acid molecules and the electrospinning technology, 5.87 at.% of B and 5.91 at.% of N atoms were doped into carbon nanofibers. Specifically, B/N electrocatalytic active centers (including BC3, pyridinic-N/CoNC, pyrrolic-N, and graphitic-N) of approximately 8.70 at.% were successfully introduced into the skeletons of Co@BN-PCNFs-900. In 0.1 M KOH, the ORR onset potential (Eonset) and half-wave potential (E1/2) of Co@BN-PCNFs-900 were ∼ 64 and ∼ 63 mV, respectively, more positive than those of 20 wt% Pt/C. Additionally, in 0.5 M H2SO4, the ORR Eonset and E1/2 values of Co@BN-PCNFs-900 were only ∼ 11 and ∼ 7 mV, respectively, more negative than those of 20 wt% Pt/C. As the 3D hierarchically porous architectures, topological carbon edges, BC3, and partial NC/CoNC are relatively stable, the Co@BN-PCNFs-900 exhibits excellent stability toward ORR catalysis in both acidic and basic media. These favorable properties of Co@BN-PCNFs-900 nanofibers make them the best non-noble metal-based carbonaceous electrocatalysts for ORR in acidic electrolytes.

Case Study on the Reproducibility of Characterizing the Electrocatalytic Activity of La1−xSrxMnO3 in ORR

The electrocatalytic activity characterization of the oxygen reduction reaction (ORR) is commonly characterized using a rotating disk electrode (RDE) with linear sweep voltammetry (LSV) or cyclic voltammetry (CV) measurements. Despite the wide application of this method in the literature, its reproducibility and comparability are rarely mentioned in articles. LSV and CV are sensitive to experimental conditions, thus the reproducibility is a significant concern. In this article, the perovskite oxides La1−xSrxMnO3 (LSMOx, x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) are chosen for the case study to measure their electroactivity using the RDE method. The main elements that influence the reproducibility of the experiment are presented and the corresponding explanations as well as the means for ensuring the reproducibility are given. Through the case study of LSMOx with variations in x and calcination temperatures, the values for the kinetic current of ORR on different catalysts are compared. It is found that doping ratios above 0.1 are associated with higher ORR electroactivity, with around a 50 mV difference in ORR onset potential between x > 0.1 and x = 0.1, which is in accordance with the results of reported works, whereas there is no significant difference when x = 0.2–0.5. Calcination temperature has little influence on the electroactivity of LSMOx, resulting in only a slight advantage at lower calcination temperatures, with an ORR onset potential that is around 10 mV more positive.

Bio-derived FeNi alloy confined in N-doped carbon nanosheets as efficient air electrodes for Zn-air battery.

It is imperative to design and manufacture electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for popularization of rechargeable Zn-air batteries. Herein, FeNi alloy confined in N-doped carbon nanosheets (FeNi@NCSs) was harvested via a facile complexation-pyrolysis strategy from the mixture of guanine and metal chlorides. After strictly exploring the pyrolysis temperature and metal types, the resulted FeNi@NCSs showed greatly improved performances on both the ORR (onset potential of 0.93V and half-wave potential of 0.84V) and OER (overpotential of 318mV at 10mAcm-2 and 379mV at 100mAcm-2). Further, the FeNi@NCSs based Zn-air battery exhibited a higher open circuit voltage (1.496V), a larger power density (128.8mWcm-2), and prominent durability (360 cycles, 120h). This study provides an appealing approach to utilize biomass for synthesis of low-cost and high-efficiency electrocatalysts in energy associated systems.

Improved trifunctional electrocatalytic performance of integrated Co3O4 spinel oxide morphologies with abundant oxygen vacancies for oxygen reduction and water-splitting reactions

A simple and surfactant-free hydrothermal method was used to produce different forms of integrated nanostructures of Co3O4 spinel oxides, which exhibited excellent trifunctional electrocatalytic activity toward oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The surface morphology and structural features of Co3O4 spinel oxide catalysts were investigated, and 40–70-nm nanocube particles were found decorated over petal-, slab-, and flower-like spinel oxide structures with the dominant (111) crystalline plane. According to physicochemical studies, the Co3O4 spinel oxide catalyst with the slab morphology has a high Co3+/Co2+ ratio and an abundance of oxygen vacancies, resulting in improved trifunctional performance with an early ORR onset potential (0.91 V), low overpotential for OER (460 mV) and HER (363 mV), and extended durability. This study provides insights into the design and structural features of Co3O4 spinel oxides through a simple and template-free synthesis approach to compete as an efficient trifunctional electrocatalyst for water splitting and metal–air battery applications.