ORR Catalysts Research Articles

Single-Cu-atoms anchored on 3D macro-porous carbon matrix as efficient catalyst for oxygen reduction and Pt co-catalyst for methanol oxidation

Single metal atoms immobilized on a carbon substrate are of great potential for enhancing the catalytic activities for oxygen reduction and methanol oxidation reactions (ORR/MOR) owing to the maximized atom utilization. Herein, single copper atoms (SCAs) are loaded on macro-porous nitrogen-doped carbon (Cu-NC) derived from zeolitic imidazolate framework-8 (ZIF-8), which are used as catalysts for ORR and Pt-supports for MOR. For ORR, the catalyst marked as Cu-NC-3 exhibits a higher peak potential of 0.87 V (vs. Reversible hydrogen electrode) than that of commercial Pt/C (0.83 V), mainly attributing to that the 3D macro-porous structure of Cu-NC-3 provides adequate space for uniform dispersion of SCAs as the main active species, and smooth diffusion pathways for fast transport of substances (O2, H2O), therefore reducing the overpotential and the intermediate (H2O2) generation to enhance ORR activity. For MOR, Pt-Cu-NC-3 has a higher mass activity of 1217.4 mA/mgPt than that of Pt/C (752.4 mA/mgPt), and its activity maintenance (decline of 27.6%) is also better than Pt/C (decline of 44.0%) after 5000 cyclic voltammetry (CV) cycles. The interactions between SCAs and Pt nanoparticles should facilitate the generation of OH− from water molecules, which can fast eliminate the adsorbed CO to recover the Pt active sites to improve MOR performance. This synthesis strategy affords a new inspiration to prepare single metal atoms loaded on ZIFs-derived macro-structure with diverse activities for ORR/MOR.

Porogen-in-Resin-Induced Fe, N-Doped Interconnected Porous Carbon Sheets as Cathode Catalysts for Proton Exchange Membrane Fuel Cells.

The high dependence of cathodic oxygen reduction reaction on precious Pt catalysts hinders the large-scale commercialization of proton exchange membrane (PEM) fuel cells, while the most promising alternative FeNC catalyst cannot achieve satisfying fuel cell performance yet. By considering the different requirements of atomically dispersed FeNC catalyst on the mass-transfer structure from that of nanoparticle Pt-based catalysts, this work develops a "porogen-in-resin" strategy to approach the Fe, N-doped interconnected porous carbon sheet (ip-FeNCS) catalyst. Three-dimensional (3D) interconnected porous structure and two-dimensional (2D) nanosheet morphology are therefore facilely combined in ip-FeNCS to simultaneously achieve the requirements on the transfer of reactants and accessibility of FeN active sites. Not only great ORR activity can be achieved under both alkaline and acid conditions but also the ip-FeNCS catalyst shows superb activity in practical PEM fuel cells from the high power output to 413 mW/cm2. Such fuel cell performance places this ip-FeNCS catalyst among the best FeNC ORR catalysts reported thus far. This work presents a general and facile approach toward the mass-transfer structure engineering of atomically dispersed carbon catalysts for practical PEM fuel cell applications.

Fabrication of bimetallic Co/Zn leaf blade structure template derived Co3O4-ZIF/Zn and its ORR catalytic performance for MFC

BackgroundThe design of highly active non-noble metal oxidation reduction catalysts (ORR) for microbial fuel cell (MFC) has always been a challenge. The aim of this study is to develop a highly active low cost cobalt-based ORR catalyst for MFCs cathode. MethodHerein, a series of highly active nitrogen doped Co3O4-ZIF/Zn-T catalysts with different calcination temperatures (T) were prepared using bimetallic Co/Zn leaf blade structure Co-ZIF/Zn-67 as template. The Co3O4-ZIF/Zn-T catalysts were characterized by various methods, and the effect of T on the structure and ORR performance of MFC catalyst were studied. Significant findingsThe results showed that the Co3O4-ZIF/Zn-T derived from bimetallic Co/Zn leaf blade structure Co-ZIF/Zn-67 template exhibited better ORR performance than Co3O4-ZIF-400 derived from the dodecahedral structure Co-ZIF-67 template. The bimetallic Co/Zn Co-ZIF/Zn-67 template promotes more uniformly distributed mesopores, high N content and abundant smaller active Co3O4 sites due to its particular structure and the isolation effect of Zinc. Among Co3O4-ZIF/Zn-T catalysts, the Co3O4-ZIF/Zn-400 calcined at 400 °C demonstrated the highest ORR performance (onset potential was 0.082 V and MFC power density was 656.9 mw/m2), which was much higher than Co3O4-ZIF-400 (0.027 V and 402.8 mw/m2). The output voltage of MFC with Co3O4-ZIF/Zn-T exhibited no significant downward trend in 30 days stability test, indicating that the Co3O4-ZIF/Zn-400 catalyst has great stability.

CuMnO2 Nanoflakes as Cathode Catalyst for Oxygen Reduction Reaction in Magnesium-Air Battery

Developing efficient and stable ORR catalysts for Mg-air batteries is crucial to enabling extensive applications. Herein, CuMnO2 nanoflakes were synthesized with a facile one-step hydrothermal way and applied as the cathode catalyst for Mg-air batteries. The ORR activities in alkaline and neutral electrolyte were then investigated. The half-wave potential has a minus variation of 22 mV after 5000 cycles, indicating the outstanding stability of the CuMnO2. The electron transfer number of the CuMnO2 is 3.70 under neutral condition, which demonstrates that the reaction process of ORR is equivalent to the commercial Pt catalyst. Moreover, the primary Mg-air battery with CuMnO2 as the cathode catalyst was assembled and the discharge properties were tested. The open circuit voltage achieved was 1.78 V and the operating voltage remained about 1.36 V after 22 h operation at 1.0 mA·cm−2. It is evident that the CuMnO2 nanoflake is an effective catalyst to accelerate the reaction rate of ORR process in Mg-air battery. This work provides a novel approach for the subsequent exploration of non-noble metal catalysts for Mg-air batteries.

Multifunctional N and O co-doped 3D carbon aerogel as a monolithic electrode for either enzyme immobilization, oxygen reduction and showing supercapacitance

Herein, a novel N and O co-doped three dimensional (3D) hybrid carbon aerogel (CA) was prepared by a two-step carbonization technology, i.e. preoxidation process (240 °C, air atmosphere) and carbonization process (600∼1000 °C, nitrogen atmosphere). It was found that the peroxidation process could improve the thermostability and heteroatoms content during the carbonization. The obtained CA samples inherited their original morphology of “string-bead” network and had a higher heteroatoms content, while the control samples did not. We focused on the application of this CA in either lactate oxidase-modified, super-capacitive and oxygen reductive electrodes. The fabricated lactate-powered integrated electronic skin could produce a maximum power density of ca. 1.3 mW cm−2, which allowed powering a multiplexed metabolic electronic in situ. The sample of CF-PVA-PANI800 showed the highest specific capacitance of 427.2 F g−1 at a discharge specific current of 0.5 A g−1. The synergistic effect of the N functionalities endowed the sample of CF-PVA-PANI900 with similar electrocatalytic activity to a 20 wt% commercial Pt/C catalyst for ORR. This fabrication strategy of carbon aerogel may provide a new alternative for preparing more heteroatom-doped 3D carbon materials in future.

FeCo/FeCoP encapsulated in N, Mn-codoped three-dimensional fluffy porous carbon nanostructures as highly efficient bifunctional electrocatalyst with multi-components synergistic catalysis for ultra-stable rechargeable Zn-air batteries

Currently, it is critical but a tricky point to develop economical, high-efficiency, and durable non-precious metal electrocatalysts towards oxygen reduction and oxygen evolution reaction (ORR/OER) in rechargeable Zn-air batteries. Herein, N, Mn-codoped three-dimensional (3D) fluffy porous carbon nanostructures encapsulating FeCo/FeCoP alloyed nanoparticles (FeCo/FeCoP@NMn-CNS) are prepared by one-step pyrolysis of the metal precursors and polyinosinic acid. The optimized hybrid nanocomposite (obtained at 800 °C, named as FeCo/FeCoP@NMn-CNS-800) exhibits outstanding catalytic performance in the alkaline electrolyte with a half-wave potential (E1/2) of 0.84 V for the ORR and an overpotential of 325 mV towards the OER at 10 mA cm−2. Impressively, the FeCo/FeCoP@NMn-CNS-800-assembled rechargeable Zn-air battery presents an open-circuit voltage of 1.522 V (vs. RHE), a peak power density of 135.0 mW cm−2, and long-term durability by charge-discharge cycling for 200 h, surpassing commercial Pt/C + RuO2 based counterpart. This work affords valuable guidelines for exploring advanced bifunctional ORR and OER catalysts in rational construction of high-quality Zn-air batteries.

Uniform Distribution of Pd on GO-C Catalysts for Enhancing the Performance of Air Cathode Microbial Fuel Cell

Metal, as a high-performance electrode catalyst, is a research hotspot in the construction of a high-performance microbial fuel cell (MFC). However, metal catalyst nanoparticles and their dispersed carriers are prone to aggregation, producing catalytic electrodes with inferior qualities. In this study, Pd is uniformly dispersed on the graphene framework supported by carbon black to form nanocomposite catalysts (Pd/GO-C catalysts). The effect of the palladium loading amount in the catalyst on the catalytic performance of the air cathode was further studied. The optimized metal loading afforded a reduced resistance and improved accessibility of Pd particles for the ORR. The maximum current output of the 0.250 Pd (mg/cm2) MFC was 1645 mA/m2, which is 4.2-fold higher than that of the carbon paper cathode. Overall, our findings provide a novel protocol for the preparation of high-efficient ORR catalyst for MFCs.

Soybean powder enables the synthesis of Fe–N–C catalysts with high ORR activities in microbial fuel cell applications

The development of microbial fuel cells (MFCs) into a new type of carbon-neutral wastewater treatment technology requires efficient and low-cost oxygen reduction reaction catalysts in air cathodes. The use of raw soybean powder was investigated for synthesizing Fe–N–C ORR catalysts in a sacrificial SiO2 support method. ZnCl2 etching in the synthesis was found to facilitate the formation of hierarchical porous structures of Fe–N–C catalysts. Fe–N–C(1-1) catalyst synthesized with an optimal soybean/ZnCl2 mass ratio of 1:1 exhibited the highest ORR activity in air cathodes. The use of the obtained Fe–N–C(1-1) catalyst enables a maximum power production of ~0.480 mW cm−2 in MFCs, higher than commercial Pt/C (0.438 mW cm−2) with the same catalyst loading of 2 mg cm−2. Long-term MFC operations demonstrated that the Fe–N–C synthesized from raw soybean have high stability and toxic tolerance, indicating that abundant low cost soybean biomass is a potential material for ORR catalyst development in MFC applications.

Rational design and mass-scale synthesis of guar-derived bifunctional oxygen catalyst for rechargeable Zn-air battery with active sites validation

The development of bifunctional OER and ORR catalysts for reversible energy storage is challenging due to the requirement of both catalytic activity and stability in a broad potential range. Under the circumstance, rational catalyst design based on fundamental understanding of redox-active sites becomes particularly meaningful. Herein, we report a facile and low-cost approach utilizing natural guar gum to fabricate a high-performance bifunctional catalyst in mass scale incorporating both the CoP and Co-N-C moieties to afford simultaneous OER and ORR activities that are comparable to RuO2 and Pt/C, respectively. Through exquisitely performed control studies, post-reaction analyses, and operando investigations, the OER and ORR active sites are validated as per initial catalyst design. Rechargeable Zinc-air batteries are further demonstrated manifesting energy efficiency, cycling stability, and high power density. This study marks the power of rational catalyst design by contriving redox-targeting moieties into hierarchical carbon scaffold to impart the desired functionalities.

Highly dispersed MnO nanoparticles supported on N-doped rGO as an efficient oxygen reduction electrocatalyst via high-temperature pyrolysis

Transition metal-based compounds, due to their excellent ORR catalytic performance under alkaline condition, have recently emerged as one of the most promising alternatives to noble metal-based ORR catalysts. It is worth noting that manganese oxide can take an unique advantage for decomposition of intermediate adsorption products H2O2 and can effectively reduce O2 to OH−. However, most research has focused on MnO2, while attention has rarely been paid to MnO catalysts. In addition, under high-temperature pyrolysis condition, MnO is the most stable manganese oxide but MnO nanoparticles easily agglomerate. Hence, it is very difficult to obtain well-dispersed and small-sized MnO nanoparticles. Herein, on the basis of pre-synthesizing uniformly distributed manganese complexes on the reduced graphene oxide (rGO), we innovatively prepare highly dispersed and small-sized MnO nanoparticles (~3.94 nm) via high-temperature pyrolysis, which are uniformly anchored on N-doped reduced graphene oxide (NrGO) as an efficient oxygen reduction electrocatalyst. The as-obtained MnO/NrGO (1050 °C) electrocatalyst achieves satisfactory onset potential (0.942 V) and half-wave potential (0.820 V) under alkaline condition. And the limiting current density is 4.17 mA cm−2, which is very close to that of Pt/C (20 wt%, JM). Meanwhile, MnO/NrGO (1050 °C) catalyst presents superior longstanding durability and methanol resistance than Pt/C (JM). This work indicates that high-temperature pyrolysis can improve the purity of manganese oxide, simultaneously the defects of NrGO can reduce particle size of MnO nanoparticles, which are greatly beneficial to improve ORR performance. This work provides a new idea for research of MnO catalysts for ORR in the future.

Tailoring Electropolymerized Poly(3,4‐ethylenedioxythiophene) Films for Oxygen Reduction Reaction

AbstractOxygen reduction reaction (ORR) is a critical process for several electrocatalytic and photocatalytic devices. Poly(3,4‐ethylenedioxythiophene), PEDOT, is an efficient ORR catalyst, with hydrogen peroxide (H2O2) being the primary reaction product. Although H2O2 is a green fuel for batteries and fuel cells and used as an industrial oxidant, it is toxic for living systems. As such, its production should be limited when PEDOT films are used in bioelectronic devices. In this work, the ORR behavior of a series of electropolymerized PEDOT films is investigated. By varying the counterion (monomeric vs polymeric), including a hydroxyl‐terminated EDOT monomer in the polymer architecture, or adding a conductivity enhancer in the reaction mixture, the authors aim to understand the parameters governing the ORR properties. It is that the polymer's pristine doping level—influenced by counterion type and the presence of the conductivity enhancer—controls the ORR pathway in PEDOT films. High levels of intrinsic doping led to films with H2O2 as the major ORR product. This work suggests strategies for the design of conducting polymers with optimized performance for electrocatalytic applications and minimized production of harmful chemicals for bioelectronic devices.

Eco-Friendly Nitrogen-Doped Graphene Preparation and Design for the Oxygen Reduction Reaction.

Four N-doped graphene materials with a nitrogen content ranging from 8.34 to 13.1 wt.% are prepared by the ball milling method. This method represents an eco-friendly mechanochemical process that can be easily adapted for industrial-scale productivity and allows both the exfoliation of graphite and the synthesis of large quantities of functionalized graphene. These materials are characterized by transmission and scanning electron microscopy, thermogravimetry measurements, X-ray powder diffraction, X-ray photoelectron and Raman spectroscopy, and then, are tested towards the oxygen reduction reaction by cyclic voltammetry and rotating disk electrode methods. Their responses towards ORR are analysed in correlation with their properties and use for the best ORR catalyst identification. However, even though the mechanochemical procedure and the characterization techniques are clean and green methods (i.e., water is the only solvent used for these syntheses and investigations), they are time consuming and, generally, a low number of materials can be prepared, characterized and tested. In order to eliminate some of these limitations, the use of regression learner and reverse engineering methods are proposed for facilitating the optimization of the synthesis conditions and the materials’ design. Thus, the machine learning algorithms are applied to data containing the synthesis parameters, the results obtained from different characterization techniques and the materials response towards ORR to quickly provide predictions that allow the best synthesis conditions or the best electrocatalysts’ identification.

Nitrogen−carbon materials base on pyrolytic graphene hydrogel for oxygen reduction

HypothesisOxygen reduction reaction (ORR) has played a significant role in the utilization of energy nowadays. Nitrogen−doped carbon materials are seen as promising catalysts for ORR, so it is of great significance in studying the functions of different nitrogen moieties. ExperimentsThe graphene hydrogel−based nitrogen−arbon materials (GH N−C) were fabricated by first obtaining a gel through hydrothermal treatment using graphene oxide (GO) as precursor, and then calcined in an ammonia atmosphere at different temperatures to form N−doped graphitized materials with divers nitrogen configuration. FindingsGH N−C materials with tunable nitrogen configuration were synthesized by a two−step method base on graphene hydrogel. Benefiting from the 3D hydrogel structure, rich defects and optimized chemical properties, GH N−C−900 prepared by NH3 pyrolysis at 900 °C exhibits an excellent electrocatalytic performance toward ORR, with the onset potential of 0.947 ± 0.013 V versus RHE, half−wave potential of 0.830 ± 0.010 V versus RHE, electron transfer number of 3.61–3.99, along as methanol tolerance and superior long−term stability. Comprehensive studies have shown that there is a positive correlation between the total amount of pyrrolic−N and quaternary−N and the catalytic performance of ORR.

Biomass-derived bifunctional electrocatalysts for oxygen reduction and evolution reaction: A review

Oxygen electrode catalysts are important as inter-conversion of O2 and H2O is crucial for energy technologies. However, the sluggish kinetics of oxygen reduction and evolution reactions (ORR and OER) are a hindrance to their scalable production, whereas scarce and costly Pt and Ir/Ru-based catalysts with the highest electrocatalytic activity are commercially unviable. Since good ORR catalysts are not always efficient for OER and vice versa, so bifunctional catalysts on which OER and ORR occurs on the same electrode are very desirable. Alternative catalysts based on heteroatom-doped carbon nanomaterials, though showed good electrocatalytic activity yet their high cost and complex synthesis is not viable for scalable production. To overcome these drawbacks, biomass-derived heteroatom-doped porous carbons have recently emerged as low-cost, earth-abundant, renewable and sustainable environment-friendly materials for bifunctional oxygen catalysts. The tunable morphology, mesoporous structure and high concentration of catalytic active sites of these materials due to heteroatom (N)-doping could further enhance their ORR and OER activity, along with tolerance to methanol crossover and good durability. Thus, biomass-derived heteroatom-doped porous carbons with large surface area, rich edge defects, numerous micropores and thin 2D nanoarchitecture could be suitable as efficient bifunctional oxygen catalysts. In the present article, synthesis, N-doping, ORR/OER mechanism and electrocatalytic performance of biomass-derived bifunctional catalysts has been discussed. The selected biomass (chitin, eggs, euonymus japonicas, tobacco, lysine and plant residue) except wood, act as both C and N precursor, resulting in N self-doping of porous carbons that avoids the use of toxic chemicals, thus making the synthesis a facile and environment-friendly green process. The synthetic strategy could be further optimized to develop future biomass-based N self-doped porous carbons as metal-free high performance bifunctional oxygen catalysts for commercial energy applications. Recent advances and the importance of biomass-based bifunctional oxygen catalysts in metal-air batteries and fuel cells has been highlighted. The material design, perspectives and future directions in this field are also provided.

Application of Non‐Precious Bifunctional Catalysts for Metal‐Air Batteries

Zinc‐air batteries have several advantages in comparison with the lithium‐ion technology as they enable the use of earth‐abundant elements, work at low cost, are lightweight, and are also much safer in application. In addition to the chemistry related to the zinc electrode, efficient and stable bifunctional catalysts are required for oxygen reduction reaction (ORR, for discharging) and oxygen evolution reaction (OER, for charging) on the air‐electrode side. Herein, a family of non‐precious metal catalysts is investigated as possible bifunctional composite: metal–nitrogen–carbon (MNC) catalysts for ORR, and metal oxyhydroxides as OER catalysts (Ox). The effect of transition metal and metal loading in these composite MNC + Ox catalysts on ORR and OER activities in half‐cell measurements is discussed. The catalysts were characterized using X‐ray diffraction and Raman spectroscopy to identify their phase composition. For the most active material, a potential gap of 0.79 V between OER and ORR was obtained, respectively. In a zinc‐air cell, this catalyst moreover showed a peak power density of 62 mW cm−2 and a charge–discharge gap of 0.94 V after 26 h of charge–discharge cycling.

Design and Mechanistic Understanding of Earth-Abundant Metal Chalcogenide Electrocatalysts for Selective Electrosynthesis of Hydrogen Peroxide

Hydrogen peroxide (H2O2) is a versatile and green oxidant with a variety of distributed applications such as environmental remediation, disinfection, and household sanitation, but its centralized chemical production via the anthraquinone process poses significant cost, energy, and safety concerns. Decentralized electrosynthesis using renewable electricity to selectively reduce O2 to H2O2 via the two-electron oxygen reduction reaction (2e- ORR) could better satisfy end-user demands on-site, yet robust, earth-abundant catalysts that are active and selective in acidic (or neutral) solutions are lacking. Here we present our recent joint efforts combining theory and experiments to establish rational design rules for selective and stable acidic 2e- ORR electrocatalysts based on earth-abundant metal chalcogenide compounds. We first showed that pyrite-type cobalt disulfide (CoS2) selectively catalyzes the acidic 2e- ORR at low overpotentials due to the spatial separation of active metal sites by anions, which kinetically suppresses the scission of O-O bond in OOH* adsorbate and the undesired 4e- ORR. We further established both pyrite- and marcasite-type cobalt diselenide (CoSe2) polymorphs as more stable and leaching-resistant acidic 2e- ORR catalysts because of the much weaker binding of O* adsorbate to Se sites. This stability allows for the bulk accumulation of practically useful 547 ppm H2O2 and the effective electro-Fenton degradation of organic pollutant for on-site environmental remediation. Building on the new mechanistic understanding, our ongoing developments and future perspectives of earth-abundant metal compound-based 2e- ORR electrocatalysts will also be discussed.

Tailoring the Pt Surface Oxophilicity Via Single-Atom Rh Doping for Boosting Hydrogen Oxidation/Evolution Reaction in Alkaline Electrolyte

Recently, the rapid development of the anion exchange membrane (AEM) shows a promising future in the commercialization of low cost and long-term stable AEM based fuel cells and water electrolyzers. AEM features an alkaline electrolyte, where non-precious metal ORR catalysts possess high ORR activity and can replace Pt catalysts. However, Pt is still the best selection for HOR catalysts in the alkaline medium. The HOR activity of Pt is highly pH-dependent and decreases over two orders of magnitude when pH increases from 1 to 14. Thus, the sluggish anodic HOR reaction becomes the most critical issue in the development of AEMFCs. The major reason for the slow HER/HOR process in the alkaline electrolyte is ascribed to the positive shift of potential of zero free charge (PZFC) while pH value goes up from pH = 1 to 14. As PZFC shifts to a more positive value, it becomes more difficult for OHads to get adsorbed on the Pt surface to facilitate the water dissociation or the removal of Hads. Tailoring Pt surface with a second transition metal hydroxides has been proved to be an effective method to enhance the HOR activity on Pt, but at the sacrifice of tremendous active surface Pt sites (~50%), leading to the waste of electrochemical surface area (ECSA) and the decrease of the maximum mass activity (MA). Herein, taking advantage of the single-atom tailoring strategy, we have achieved single Rh atom tailoring of Pt nanowires for the optimization of surface oxophilicity for OH adsorption to boost the HER/HOR activity in the alkaline condition.The HOR activity of PtRh nanowires is highly sensitive to the oxophilicity of Pt surface and the structure of surface Rh species. Pt surface with higher oxophilicity usually shows a higher HER/HOR rate in alkaline conditions because the sluggish Volmer step can be accelerated by the early adsorption of OH in the Hupd potential region. However, both the HOR and HER activity of the PtRh nanowires reach the maximum value only when the Rh is in the single-atom form and the Pt surface is under the optimum oxophilicity.It was revealed by the XANES spectra that the single Rh atoms under 0 V vs. RHE are positively charged. The in-situ and ex-situ XANES spectra of Rh L edge show that Rh atoms are redox-active and electroactive. The positive shift of the edge position from Rh foil to Rh single atoms under 0 V vs. RHE indicates that the single Rh atoms are slightly oxidized and coordinated with eight Pt and one O, even under 0 V vs. RHE. When the applied potential increases, Rh-O bond intensity increases, and Rh-Pt bond intensity decreases, as expected from the oxidation from slightly charged single atom Rh to single Rh(OH)x species. We also noted that the Rh-O peak shift positively when potentials shifts from 0.54 V to 0 V vs. RHE, indicating an elongated Rh-O bond at a lower overpotential, which indicates that the adsorbed oxygen species under 0 V are not the OH from Rh(OH)x and should be weakly adsorbed OH or H2O↓. The fitting of in-situ EXAFS of Rh L edge on the SARh-PtNWs also confirms that the Rh atoms are bonded with eight Pt atoms and one O, and no Rh-Rh interaction is found throughout the whole HOR range.The existence of single atom Rh-OHads or Rh-H2O↓ under 0 V vs. RHE significantly facilitates the sluggish Volmer step at the minimal sacrifice of the active Pt sites where H2 dissociation and H adsorption takes place. When the surface Rh concentration surpasses a critical point, singly dispersed Rh atoms start to aggregate to a continuously distributed Rh layer which significantly increases the surface oxophilicity for earlier OH adsorption, but at the sacrificial of highly active Pt site for H2 dissociation and high Hads surface coverage. HOR/HER requires an equilibrium of H adsorption and OH/H2O adsorption on the Pt surface to reach the maximum oxidation/production rate of H2. However, both the Tafel step and the Volmer step on the Rh rich Pt surface are far away from the optimum condition, Also, the excess Rh and adsorbed water may form a rigid water layer that covers the Pt surface and prevent it from accessing the H2, results in the decreased overall HOR activity.In short, we have synthesized single atom Rh tailored Pt nanowires and used in-situ EXAFS and XANES to prove the existence of the surface Rh-OHads or Rh-H2O↓ which significantly facilitate the HER and HOR process. Figure 1

The Role of Sulfur Doping in Determining the Performance of Fe/N-C Based Electrocatalysts for Oxygen Reduction Reactions

The effect of S-doping on the performance of Fe/N-C catalysts for ORR was studied. It was found that the abundant C–S–C bonds in the sulfur-doped catalysts enhanced the ORR activity greatly, while the existence of excessive C-SOX-C bonds was adverse to the kinetics of ORR. Also, the existence of Fe was able to increase the contents of both C–S–C bond and graphite N during the pyrolysis stage of preparation, thus generating more ORR active sites. The resulted effective configurations of S (C–S–C) and active N (both graphitic N and pyridinic N), and the combination of rich hierarchical porous structure with the encased Fe3C nanoparticles were responsible for the excellent performance of catalysts. Specifically, the E1/2 of the prepared FeNSC-10S catalyst reached 0.91 V in a 0.1 M KOH electrolyte solution, which was 20 mV positive shift to the E1/2 of the 20 wt.% Pt/C commercial catalyst. The electron transfer number was determined to be 3.85−3.91 over the potential range of 0.4−0.8 V, indicating that the ORR catalytic process proceeded in a reaction pathway with nearly 4e− transfer. The developed catalyst also demonstrated a long-term stability as well as a superior methanol tolerance in alkaline conditions.

First-principle calculations study of pristine, S-, O-, and P-doped g-C3N4 as ORR catalysts for Li-O2 batteries

In this work, we investigated the ORR process on the surface of graphitic carbon nitride (g-C3N4), S-, O-, and P-doped g-C3N4 by the DFT method. According to the results, the reaction begins with Li adsorption and the first adsorbed Li atom is probably trapped on the considered substrates so the ORR process was also investigated on the surface with one trapped Li atom. The overpotential of the discharge process was obtained as 0.41 V for g-C3N4.S and 0.84 V for g-C3N4.S/Li which indicates that g-C3N4.S could be a promising candidate for application in Li-O2 battery.

Multi-doped carbon derived from notoginseng as a high-performance catalyst for oxygen reduction

Developing highly active electrocatalysts for oxygen reduction reaction to replace platinum is key to many advanced energy systems. In this work, a high-performance ORR catalyst is fabricated by using notoginseng as the precursor through a simple pyrolysis process. The catalyst exhibits high catalytic performance towards ORR comparable with that of commercial Pt/C catalyst, as well as outstanding stability and rather high four-electron path selectivity during the ORR procedures. It is suggested that the porous structure, self-doping of nitrogen, and the trace Fe impurities display the crucial role for the superior ORR activity and outstanding stability of PPG.