Oxygen Reduction Reaction Catalysts Research Articles

NC Loaded PtM Alloy from M-NC with Ultralow Pt Loading for Oxygen Reduction Reaction

Developing low Pt or non-precious metal catalysts for oxygen reduction reaction (ORR) has becoming necessary in recent years. Herein, PtM alloy anchored on nitrogen-doped carbon (PtM/NC, M=Fe, Co) catalyst with ultralow Pt loading (∼1 wt%) is prepared from the simple two-process pyrolysis, namely from C to M-NC then to PtM/NC. The as-prepared PtM/NC (M=Fe, Co) shows an excellent ORR catalytic performance with the peak potential and half-wave potential of 0.901 and 0.870 V for PtFe/NC, 0.868 and 0.845 V for Pt3Co/NC. The ORR on PtM/NC (M=Fe, Co) is a mainly direct 4-electron reaction pathway (3.75–3.90) in alkaline solution. Moreover, they possess good methanol tolerance and stability. Synergistic effect of Pt and M together with N species result in the excellent ORR catalytic activity of PtM/NC (M=Fe, Co). The negative shift of Pt binding energy caused by both lattice contraction and electron orbital coupling from M is beneficial for reducing the d-band center of Pt, weakening the oxygen binding energy and enhancing the ORR intrinsic activity of Pt. The strong interactions between NC and PtM alloy are beneficial for anchoring PtM nanoparticles, promoting the stability of catalyst. This work provides a new strategy for preparing ultralow Pt loading catalysts.

Nickel adsorbed algae biochar based oxygen reduction reaction catalyst

Lately, the bio electrochemical systems are emerging as an efficient wastewater treatment and energy conversion technology. However, their scaling-up is considerably restrained by slow-rate of cathodic oxygen reduction reaction (ORR) or otherwise by the high cost associated with the available efficient ORR catalysts. In this investigation, a cost-effective and eco-friendly approach for synthesizing Ni based ORR catalyst utilizing biosorption property of microalgae is accomplished. The synthesised Ni adsorbed algal biochar (NAB) served as an efficient cathode catalyst for enhancing ORR in a microbial carbon-capture cell (MCC). On increasing the initial concentration of Ni2+ in the aqueous medium from 100 mgL−1 to 500 mgL−1, the biosorption capacity was found to increase from 3 mgg−1 to 32 mgg−1 of algae cell. The MCC operated with NAB based cathode catalyst loading of 2 mgcm-2 exhibited 3.5 times higher power density (4.69 Wm−3) as compared to the one with commercial activated carbon. A significant organic matter removal (82 %) in the anodic chamber with simultaneous algal biomass productivity in the cathodic chamber was attained by MCC with cathode loaded with 2 mgcm−2 of NAB. Hence, this easily synthesised low-cost catalyst, out of waste stream, proved its ability to improve the performance of MCC.

Enhanced corrosion protection of rebars in alkaline solutions by ferroporphyrin and the mechanisms of electron consumption and lattice reconstruction

Abstract Reinforced concretes are the primary materials in coastal and offshore engineering. In alkaline environment of concrete, the anodic process is passivation of rebars and the conjugated cathodic process is oxygen reduction reaction (ORR). It is proposed that a novel approach to enhance the passivation films through catalyzed ORR by iron meso-tetra(4-carboxyphenyl)porphine (FeTCPP). The ORR catalyst FeTCPP promotes the formation of passivation film, as it accelerates the consumption of abundant electrons generated and accumulated by the anodic formation of passivation films. The passivation films of rebars are highly defective Fe3O4 semiconductor. The dissolution of interstitial ferrous ions and lattice iron ions produces defects of O ion vacancies, Fe ion vacancies and interstitial Fe ions, and they further cause the formation and accumulation of Fe atom vacancies on the metal surface, leading to the collapse of the passivation films. The FeTCPP adsorbs on the surface of passivation films, hindering the dissolution of lattice iron ions and interstitial ferrous ions, thereby inhibiting the generation and accumulation of Fe atom vacancies and improving the integrity and protective ability of the passivation films.

Synthesis of biomass nitrogen-doped catalysts and their electrocatalytic performance in fuel cells

At present, biomass materials have the characteristics of low cost, stability, and relatively high activity, which is expected to replace platinum-based (Pt) materials as cathode catalysts. In this paper, Zn, Fe-N-C catalyst materials and Fe-N-C catalyst were composited by high-temperature calcination. Their crystal and morphological structures were featured by X-ray diffraction instruments (XRD) and scanning electron microscopy (SEM). Their activity and stability to oxygen reduction were tested by an electrochemical workstation, and it was found that Zn, Fe-N-C catalyst materials had the best performance. The investigation of this paper can furnish an effective method for oxygen reduction reaction catalysts.

Theoretical insights on 3D transition metal anchored poly[5,10,15,20-tetra(4-ethynylphenyl)porphyrin]diyne as highly efficient bifunctional catalyst toward ORR and OER

Searching for highly active oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts is a challenging task in the development of clean energy devices. Herein, by using the poly[5,10,15,20-tetra(4-ethynyl-phenyl)porphyrin]diyne (TEPPD), we designed ORR and OER catalysts by anchoring 3d transition metal into TEPPD (TM@TEPPD, TM = Mn-Zn). Our study indicated that Fe@TEPPD is the best bifunctional catalyst for both ORR and OER. By proposing a proper descriptor, Ni-N3@TEPPD (Ni is only coordinated with three N atoms) is designed and also predicted to be a promising bifunctional catalyst. For Fe@TEPPD, ORR and OER become inactive when the acetylene bond in TEPPD is broken. The surface Pourbaix diagram indicated that on the surface of Fe@TEPPD, ORR and OER can be carried out at the whole pH region due to the high dissolution potential of Fe2+. For Ni-N3@TEPPD, however, the dissolution potential 0.71 V for Ni2+is low. Thus, for Ni-N3@TEPPD, ORR can be carried out only after pH>2.54, while OER is not likely at the whole pH region. This suggested that the conclusions from the free energy changes at URHE=0 and pH=0 could be different when different potentials and pH values are considered.

Bimetallic Center Metal–Organic Framework Catalysts for the Two-Electron Oxygen Reduction Reaction

Bimetallic Center Metal–Organic Framework Catalysts for the Two-Electron Oxygen Reduction Reaction

Interlayer Polymerization to Construct a Fully Conjugated Covalent Organic Framework as a Metal-Free Oxygen Reduction Reaction Catalyst for Anion Exchange Membrane Fuel Cells.

Two-dimensional (2D) covalent organic frameworks (COFs) have a multilayer skeleton with a periodic π-conjugated molecular array, which can facilitate charge carrier transport within a COF layer. However, the lack of an effective charge carrier transmission pathway between 2D COF layers greatly limits their applications in electrocatalysis. Herein, by employing a side-chain polymerization strategy to form polythiophene along the nanochannels, a conjugated bridge is constructed between the COF layers. The as-synthesized fully conjugated COF (PTh-COF) exhibits high oxygen reduction reaction (ORR) activity with narrowed energy band gaps. Correspondingly, PTh-COF is tested as a metal-free cathode catalyst for anion exchange membrane fuel cells (AEMFCs) which showed a maximum power density of 176mWcm-2 under a current density of 533mAcm-2. The density functional theory (DFT) calculation reveals that interlayer conjugated polythiophene optimizes the electron cloud distribution, which therefore enhances the ORR performance. This work not only provides new insight into the construction of a fully conjugated covalent organic framework but also promotes the development of new metal-free ORR catalysts.

A Non‐Macrocycle Thiolate‐Based Cobalt Catalyst for Selective O2 Reduction into H2O

AbstractThe reduction of dioxygen to produce selectively H2O2 or H2O is crucial in various fields. While platinum‐based materials excel in 4H+/4e− oxygen reduction reaction (ORR) catalysis, cost and resource limitations drive the search for cost‐effective and abundant transition metal catalysts. It is thus of great importance to understand how the selectivity and efficiency of 3d‐metal ORR catalysts can be tuned. In this context, we report on a Co complex supported by a bisthiolate N2S2‐donor ligand acting as a homogeneous ORR catalyst in acetonitrile solutions both in the presence of a one‐electron reducing agent (selectivity for H2O of 93 % and TOFi=3 000 h−1) and under electrochemically‐assisted conditions (0.81 V <η<1.10 V, selectivity for H2O between 85 % and 95 %). Interestingly, such a predominant 4H+/4e− pathway for Co‐based ORR catalysts is rare, highlighting the key role of the thiolate donor ligand. Besides, the selectivity of this Co catalyst under chemical ORR conditions is inverse with respect to the Mn and Fe catalysts supported by the same ligand, which evidences the impact of the nature of the metal ion on the ORR selectivity.

Innovative Strategy for Developing PEDOT Composite Scaffold for Reversible Oxygen Reduction Reaction.

Metal-air batteries are an emerging technology with great potential to satisfy the demand for energy in high-consumption applications. However, this technology is still in an early stage, facing significant challenges such as a low cycle life that currently limits its practical use. Poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer has already demonstrated its efficiency as catalyst for oxygen reduction reaction (ORR) discharge as an alternative to traditional expensive and nonsustainable metal catalysts. Apart from that, in most electrochemical processes, three phenomena are needed: redox activity and electronic and ionic conduction. Material morphology is important to maximize the contact area and optimize the 3 mechanisms to obtain high-performance devices. In this work, porous scaffolds of PEDOT-organic ionic plastic crystal (OIPC) are prepared through vapor phase polymerization to be used as porous self-standing cathodes. The scaffolds, based on abundant elements, showed good thermal stability (200 °C), with potential ORR reversible electrocatalytic activity: 60% of Coulombic efficiency in aqueous medium after 200 cycles.

Metal–organic framework–derived trimetallic particles encapsulated by ultrathin nitrogen-doped carbon nanosheets on a network of nitrogen-doped carbon nanotubes as bifunctional catalysts for rechargeable zinc–air batteries

Economical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts with high activity aimed at replacing precious metal catalysts for rechargeable zinc-air batteries (ZABs) must be developed. In this study, a multiple hierarchical-structural material is developed using a facile dielectric barrier discharge (DBD) plasma surface treatment, solvothermal reaction, and high-temperature carbonization strategy. This strategy allows for the construction of nanosheets using nitrogen-doped carbon (NC) material-encapsulated ternary CoNiFe alloy nanoparticles (NPs) on a network of NC nanotubes (NCNTs), denoted as CoNiFe–NC@p–NCNTs. Precisely, the presence of abundant CoNiFe alloy NPs and the formation of M–N–C active sites created by transition metals (cobalt, nickel, and iron) coupled with NC can provide superior OER/ORR bifunctional properties. Moreover, the prepared NC layers with a multilevel pore structure contribute to a larger specific surface area, exposing numerous active sites and enhancing the uniformity of electron and mass movement. The CoNiFe0.08–NC@p–NCNTs show remarkable dual functionality for electrochemical oxygen reactions (ORR half-wave potential of 0.811 V, limiting current density of 5.73 mA cm−2 measured with a rotating disk electrode at a rotation speed of 1600 rpm, and OER overpotential of 351 mV at 10 mA cm−2), which demonstrates similar ORR performance to 20 wt% Pt/C and better OER performance than the commercial RuO2. A liquid ZAB prepared using the proposed material has excellent bifunctionality with an open-circuit voltage of 1.450 V and long-term cycling stability of 230 h@10 mA cm−2.

Electrode microstructure design to improve effective utilization of Fe-N/C catalysts towards oxygen reduction reaction process

Fe-N/C materials have shown intrinsic activities comparable to Pt/C catalysts for oxygen reduction reaction on rotating ring-disk electrodes (RRDE). However, due to the insufficient three-phase interfaces (TPIs) and high oxygen transport resistance (RT), the high intrinsic activity cannot be sufficiently utilized in electrodes, resulting in a gap between the intrinsic catalytic activity on RRDE and the performance in devices. To expand the TPIs and promote oxygen transport, a novel electrode with a transition layer structure is proposed to disperse the active sites. The dispersion degree of active sites is optimized by tuning the solid–liquid interfacial energy between the ink solvent and the substrate. A high electrochemical active area of 1264 cm2 and a low RT of 2.0 s cm−1 are achieved for the electrode prepared by an alcohol-rich ink. The simulation and experimental results demonstrate that the microstructure can benefit the extension of TPIs and facilitate oxygen transport in the air cathode, ultimately achieving efficient utilization of catalytic activities. A maximum power density of 35.4 mW cm−2 is achieved in a membrane-less direct formate fuel cell, surpassing most congeneric devices. Our approach clarifies the relationship between TPI construction, mass transport, and electrode microstructure, which successfully exploits the intrinsic activity on air cathodes and improves the power generation ability.

Superior Catalytic Performance and Methanol Tolerance of Co@Mesoporous Graphene Nanocomposites toward Oxygen Reduction Reaction

AbstractThe global energy crisis and growing concerns about environmental pollution have spurred researchers to explore eco‐friendly methods of generating clean energy. Previous studies have often relied on noble metal catalysts to facilitate oxygen reduction reactions (ORR) in energy production reactions. However, their high cost has limited their widespread adoption, making the development of highly active and affordable ORR catalysts a significant challenge. In this study, a vacuum heat treatment technique was employed to fabricate a cobalt‐loaded mesoporous graphene (Co−Gs) nanocomposite. The inclusion of cobalt in graphene enhances the reaction, while the presence of mesoporous graphene provides a larger surface area to accommodate the active sites of Co. This synergistic effect promotes the improvement of catalytic performance. Additionally, the stability and methanol tolerance of Co−Gs nanocomposites is also superior than that of Pt−C. The excellent catalytic performance of the Co−Gs nanocomposite is attributed to a four‐electron pathway within the nanocomposite, as demonstrated by electrocatalytic kinetics investigations. Additionally, the interface interaction between the Co nanoparticles and Gs enhances the efficiency of electron transfer, effectively improving the catalytic performance. These findings highlight the potential of Co‐loaded graphene nanocomposites as highly efficient and cost‐effective electrocatalysts for clean energy application.

Sulfur-Tuned Main-Group Sb-N-C Catalysts for Selective 2-Electron and 4-Electron Oxygen Reduction.

The selective oxygen reduction reaction (ORR) is important for various energy conversion processes such as the fuel cells and metal-air batteries for the 4e- pathway and hydrogen peroxide (H2O2) electrosynthesis for the 2e- pathway. However, it remains a challenge to tune the ORR selectivity of a catalyst in a controllable manner. Herein, an efficient strategy for introducing sulfur dopants to regulate the ORR selectivity of main-group Sb-N-C single-atom catalysts is reported. Significantly, Sb-N-C with the highest sulfur content follows a 2e- pathway with high H2O2 selectivity (96.8%) and remarkable mass activity (96.1 A g-1 at 0.65V), while the sister catalyst with the lowest sulfur content directs a 4e- pathway with a half-wave potential (E1/2 = 0.89V) that is more positive than commercial Pt/C. In addition, practical applications for these two 2e-/4e- ORR catalysts are demonstrated by bulk H2O2 electrosynthesis for the degradation of organic pollutants and a high-power zinc-air battery, respectively. Combined experimental and theoretical studies reveal that the excellent selectivity for the sulfurized Sb-N-Cs is attributed to the optimal adsorption-desorption of the ORR intermediates realized through the electronic structure modulation by the sulfur dopants.

High-throughput screening of dual atom catalysts for oxygen reduction and evolution reactions and rechargeable zinc-air battery

We provide the rational design of dual atom catalysts (DACs) supported on nitrogen-doped graphene for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) through high-throughput computational screening of M1M2N6-DAC systems, where M1 and M2 represent Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, or Pt metals. We predict that FeRuN6-DAC at the summit of the volcano plot exhibits a low theoretical ORR overpotential (ηORR) of 0.24 V and a low theoretical OER overpotential (ηOER) of 0.19 V. The low ηORR and ηOER result from the catalytic performance of the Fe site being tuned to electronic properties that facilitate adsorption and desorption of the OH* intermediate. Inspired by these hybrid density functional theory (DFT) computational and machine learning (ML) results, we synthesized FeRuN6-DAC, FeN4-SAC, and RuN4-SAC and characterized them using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), scanning transmission electron microscopy (STEM), and in-situ electron spin resonance (ESR). Our in-situ ESR spectroscopy signifies that the spin of the Fe active site increases with increasing applied potential due to the increase in the concentration of OH* intermediate on Fe. We verified experimentally the predicted catalytic performances, finding that FeRuN6-DAC leads to an experimental ORR overpotential of 0.29 V with a Tafel slope of 104 mVdec−1 and an OER overpotential of 0.27 V with a Tafel slope of 124 mVdec−1. The rechargeable Zinc-air battery setup was fabricated with FeRuN6-DAC in place of the cathode, showing a maximum power density of 0.45 W/cm2 at the current density of 0.44 A/cm2 and good stability after 120 cycles. According to our findings, we demonstrate that DFT-guided strategies are useful for designing advanced DACs applicable to ORR, OER, and Zinc-air battery applications.

Rational Design of Heteroatom-Doped Fe–N–C Single-Atom Catalysts for Oxygen Reduction Reaction via Simple Descriptor

Rational Design of Heteroatom-Doped Fe–N–C Single-Atom Catalysts for Oxygen Reduction Reaction via Simple Descriptor

Co-N-C axially coordination regulated H2O2 selectivity via water medicated recombination of solute •OH: A new route

The cobalt, earth abundant transition metal, embedded in nitrogen doped carbon material as single atom site (Co-N-C) has been manifested as promising electrochemical oxygen reduction reaction (ORR) catalyst, however the unsatisfying production selectivity has hampered its widespread applications. Herein, the H2O2 selectivity of Co-N-C catalyst has been tailored with Co axial functional groups. Thermodynamically, the selectivity is regulated due to the fine-tuning of the adsorption of the key reaction intermediates (ΔG*OOH), and five functional groups, including −O, –OH, –CN, −CH3 and −SO3, endow the Co-N-C catalyst with superior H2O2 selectivity. Importantly, we unravel a new water medicated recombination of solute •OH reaction pathway for H2O2 production, which was the result of dissociation of *HOOH in explicit water environment. That is, two •OH species reaction in the liquid environment which originated from the creaking of *OOH intermediates due to the weakened O-O bond by the interaction with surrounding water. This study provides foundational understanding for the ORR catalytic mechanism at the electrochemical interface and opens up new avenues for rational design of targeted high efficiency electrocatalysts.

Precisely Engineering Asymmetric Atomic CoN4 by Electron Donating and Extracting for Oxygen Reduction Reaction

AbstractThe development of nonpyrolytic catalysts featuring precisely defined active sites represents an effective strategy for investigating the fundamental relationship between the catalytic activity of oxygen reduction reaction (ORR) catalysts and their local coordination environments. In this study, we have synthesized a series of model electrocatalysts with well‐defined CoN4 centers and nonplanar symmetric coordination structures. These catalysts were prepared by a sequential process involving the chelation of cobalt salts and 1,10‐phenanthroline‐based ligands with various substituent groups (phen(X), where X=OH, CH3, H, Br, Cl) onto covalent triazine frameworks (CTFs). By modulating the electron‐donating or electron‐withdrawing properties of the substituent groups on the phen‐based ligands, the electron density surrounding the CoN4 centers was effectively controlled. Our results demonstrated a direct correlation between the catalytic activity of the CoN4 centers and the electron‐donating ability of the substituent group on the phenanthroline ligands. Notably, the catalyst denoted as BCTF−Co‐phen(OH), featuring the electron‐donating OH group, exhibited the highest ORR catalytic activity. This custom‐crafted catalyst achieved a remarkable half‐wave potential of up to 0.80 V vs. RHE and an impressive turnover frequency (TOF) value of 47.4×10−3 Hz at 0.80 V vs. RHE in an alkaline environment.

Precisely Engineering Asymmetric Atomic CoN4 by Electron Donating and Extracting for Oxygen Reduction Reaction.

The development of nonpyrolytic catalysts featuring precisely defined active sites represents an effective strategy for investigating the fundamental relationship between the catalytic activity of oxygen reduction reaction (ORR) catalysts and their local coordination environments. In this study, we have synthesized a series of model electrocatalysts with well-defined CoN4 centers and nonplanar symmetric coordination structures. These catalysts were prepared by a sequential process involving the chelation of cobalt salts and 1,10-phenanthroline-based ligands with various substituent groups (phen(X), where X=OH, CH3, H, Br, Cl) onto covalent triazine frameworks (CTFs). By modulating the electron-donating or electron-withdrawing properties of the substituent groups on the phen-based ligands, the electron density surrounding the CoN4 centers was effectively controlled. Our results demonstrated a direct correlation between the catalytic activity of the CoN4 centers and the electron-donating ability of the substituent group on the phenanthroline ligands. Notably, the catalyst denoted as BCTF-Co-phen(OH), featuring the electron-donating OH group, exhibited the highest ORR catalytic activity. This custom-crafted catalyst achieved a remarkable half-wave potential of up to 0.80 V vs. RHE and an impressive turnover frequency (TOF) value of 47.4×10-3 Hz at 0.80 V vs. RHE in an alkaline environment.

Ag@Co/Zn N‐Doped Carbon as Antibacterial Oxygen Reduction Catalysts for Microbial Fuel Cells

Biofouling of air cathode surface decreases the electricity generation performance of membrane‐free microbial fuel cells (MFCs). Ag@Co/Zn N‐doped carbon (Ag@Co/Zn‐NC) is designed as an antibacterial oxygen reduction reaction (ORR) catalyst to inhibit biofouling on the cathode surface. The Co/Zn‐NC active component promotes ORR catalytic activity through the advantages of well‐distributed Co nanoparticles and numerous active sites. Superficial Ag nanoparticles act as antibacterial active species to inhibit bacterial proliferation and suppress biofilm growth. Ag@Co/Zn‐NC catalyst prevents bacterial adhesion and biofilm formation, effectively preventing excessive biofouling on the cathode surface. The antibacterial catalyst maintains a high catalytic activity and good ion diffusion properties without the adverse effects of biofouling, resulting in enhanced ORR durability of the air cathode. The assembled MFCs achieve high electricity generation during long‐term cyclic operation. The maximum power density retention percentage (82.6%) is higher than that of Co/Zn‐NC MFC (65.3%) and Pt/C MFC (52.4%) after continuous operation for 1200 h. Excellent operational durability is revealed for the air‐cathode MFCs assembled with the antibacterial ORR catalyst during the cyclic process. The novelty of this study is that the design of antibacterial catalysts inhibits the excessive growth of the cathode biofilm to improve the cyclic electricity generation performance of MFCs.

Second-Shell N Dopants Regulate Acidic O2 Reduction Pathways on Isolated Pt Sites.

Pt is a well-known benchmark catalyst in the acidic oxygen reduction reaction (ORR) that drives electrochemical O2-to-H2O conversion with maximum chemical energy-to-electricity efficiency. Once dispersing bulk Pt into isolated single atoms, however, the preferential ORR pathway remains a long-standing controversy due to their complex local coordination environment and diverse site density over substrates. Herein, using a set of carbon nanotube supported Pt-N-C single-atom catalysts, we demonstrate how the neighboring N dopants regulate the electronic structure of the Pt central atom and thus steer the ORR selectivity; that is, the O2-to-H2O2 conversion selectivity can be tailored from 10% to 85% at 0.3 V versus reversible hydrogen electrode. Moreover, via a comprehensive X-ray-radiated spectroscopy and shell-isolated nanoparticle-enhanced Raman spectroscopy analysis coupled with theoretical modeling, we reveal that a dominant pyridinic- and pyrrolic-N coordination within the first shell of Pt-N-C motifs favors the 4e- ORR, whereas the introduction of a second-shell graphitic-N dopant weakens *OOH binding on neighboring Pt sites and gives rise to a dominant 2e- ORR. These findings underscore the importance of the chemical environment effect for steering the electrochemical performance of single-atom catalysts.