Efficient Oxygen Reduction Reaction Research Articles

Asymmetric Atomic Tin Catalysts with Tailored p‐Orbital Electron Structure for Ultra‐Efficient Oxygen Reduction

AbstractAtomically dispersed transition metal–nitrogen–carbon (M–N–C) catalysts guide by the d‐band center theory have been extensively studied for oxygen reduction reaction (ORR) in various energy conversion and storage processes. However, asymmetric p‐block metal single‐atom catalysts (SACs) toward ORR have rarely been reported, and the origin of their catalytic activity is still unclear. Here, an asymmetric N, O coordinated Sn SAC is developed as an efficient ORR electrocatalyst. Remarkably, the optimized Sn SAC (e.g., Sn–N/O–C) exhibit outstanding ORR performance with a half‐wave potential of 0.910 V in alkaline media, outperforming most state‐of‐the‐art ORR catalysts. More importantly, the Sn–N/O–C possesses a long‐term durability in both alkaline and acidic electrolytes. Besides, Zn–air batteries based on the Sn–N/O–C cathode also show a higher energy density (254 mW cm‐2) than that of their reported M–N–C counterparts. Theoretical calculations suggest that the asymmetric N, O coordinated atomic Sn sites have a stronger binding interaction with O2 and better charge transfer ability compared with the symmetric SnN4 sites, thereby facilitating the ORR process. This work provides a nitrogen‐, oxygen‐coordinated engineering strategy for the rational design of highly active and durable carbon‐based catalysts with atomic p‐block metal sites for ORR and beyond.

Biomass-derived nitrogen-doped carbons activated by zinc halides for electrocatalytic oxygen reduction reaction

Biomass-derived carbon materials are certified to be excellent catalysts for oxygen reduction reaction (ORR) and their ORR activity is severely affected by activators. For this reason, three zinc halides (ZnF2, ZnBr2, and ZnI2) and ZnCl2 used as activators for the formation of pea pod-derived carbon materials are systematically investigated for the first time. The presence of ZnX2 significantly changes the morphology of biomass-derived carbon materials and effectively increases the specific surface area, surface defect and doping content of N. These factors effectively promote the ORR activity of the product, especially PPBrNC. The four resulted carbons show high onset potential, half-wave potential and limiting current density that is comparable with Pt/C, and the obvious 4-electron reduction pathway is displayed in ORR process. Meanwhile, the ultra-high stability and methanol tolerance make it a potential non-precious metal catalyst. Therefore, ZnX2 is a class of low-cost and excellent chemical activators for the preparation of biomass-derived carbon materials and can provide a new idea for exploring low-cost, efficient and stable ORR catalysts.

An asymmetric electrode matching reversible kinetics of oxygen reaction for a rechargeable Zn-air battery

The development of zinc-air batteries (ZABs) is hindered by the sluggish kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) which occur in the complex interfaces between gaseous oxygen, liquid electrolyte and solid catalyst. Designing a rational interface that aligns with the kinetics of these multi-phase reactions is of utmost importance. Herein, an asymmetric cathode (Asy-electrode) has been designed and fabricated that the carbon nanotubes arrays (CNAs) encapsulating Co nanoparticles grown on carbon cloth is used as the aerophilic side (AI-side) to match and catalyze the ORR kinetics, the other side that deposition of NiFe layered double hydroxide (NiFe-LDH) on the CNAs plays as aerophobic side (AO-side) to accelerate the OER kinetics. The Asy-electrode effectively balances the adsorption and desorption of O2 and OH–, and promotes the efficient transport of gaseous and liquid reactants and products. Therefore, the efficiency of ORR and OER onto the corresponding catalytic sites of Co/CNAs and NiFe-LDH/CNAs are significantly enhanced. Consequently, the ZAB employing the asymmetric cathode can acquire a remarkable higher power density (236.26 mW cm−2) and an excellent long-term cycling stability (over 1920 cycles at 10 mA cm−2) due to the enhanced kinetic and the improved reversibility of the charge–discharge reaction on the cathode benefiting from the aerophilic/hydrophilic interfacial construction on each side of electrode. The present study could explore a route to design the catalysts from the view of matching the multi-phase reaction characteristics.

Recent Progress in ZIF‐Derived Carbons for Enhanced Oxygen Reduction Reaction Electrocatalysis

AbstractThe oxygen reduction reaction (ORR) represents a cornerstone for many clean energy conversion technologies such as fuel cells and metal‐air batteries. Nevertheless, the commercialization of these technologies is largely impeded by the slow kinetics of ORR, for which active, durable and cost‐effective ORR catalysts are needed. In recent years, zeolitic imidazolate framework (ZIF) derived carbon materials emerge as a new class of non‐precious metal catalysts (NPMCs) toward ORR, largely benefiting from their high surface area, abundant porosity, tunable chemical/electronic structure, and superior ORR activity which is comparable or even surpasses those state‐of‐the‐art Pt‐based ORR catalysts. This review offers a comprehensive overview of the recent advances in ZIF‐derived carbons for ORR. The synthesis strategies and the key factors affecting the ORR performance of ZIF‐derived carbon materials are discussed. Future research directions and perspectives on exploring ZIF derived carbons as efficient ORR catalysts are highlighted, with a focus on the principles of rationally engineering the coordination structures of active sites.

Regulating atomic Fe-Rh site distance for efficient oxygen reduction reaction

Regulating atomic Fe-Rh site distance for efficient oxygen reduction reaction

Computational Assistance in the Design of Efficient Oxygen Reduction Reaction Electrocatalysts

AbstractRecently, theoretical calculations have played an irreplaceable role in the discovery of electrocatalysts as a relatively time‐efficient, cost‐effective, and predictable method. More importantly, theoretical calculations can help screen out the best active reaction sites and modulate them accordingly, which is beneficial for the development of efficient catalysts. In this concept, we focus on the important role of theoretical calculations in determining catalytic active sites and understanding reaction mechanisms, emphasizing its importance in assisting the design and synthesis of efficient oxygen reduction reaction catalysts. Finally, we provide an outlook on the challenges and future development trend in this field.

Construction of Fe Nanoclusters/Nanoparticles to Engineer FeN4 Sites on Multichannel Porous Carbon Fibers for Boosting Oxygen Reduction Reaction

AbstractFe–N–C catalysts are emerging as promising alternatives to Pt‐based catalysts for the oxygen reduction reaction (ORR), while they still suffer from sluggish reaction kinetics due to the discontented binding affinity between the Fe‐N4 sites and oxygen‐containing intermediates, and unsatisfactory stability. Herein, a flexible multichannel carbon fiber membrane immobilized with atomically dispersed Fe‐N4 sites and neighboring Fe nanoclusters/nanoparticles (FeN4‐FeNCP@MCF) is synthesized. The optimized geometric and electronic structures of the Fe atomic sites brought by adjacent Fe nanoclusters/nanoparticles and hierarchically porous structure of the carbon matrix endow FeN4‐FeNCP@MCF with outstanding ORR activity and stability, considerably outperforming its counterpart with FeN4 sites only and the commercial Pt/C catalyst. Liquid and solid‐state flexible zinc–air batteries employing FeN4‐FeNCP@MCF both exhibit outstanding durability. Theoretical calculation reveals that the Fe nanoclusters can trigger remarkable electron redistribution of the FeN4 sites and modulate the hybridization of central Fe 3d and O 2p orbitals, facilitating the activation of O2 molecules and optimizing the adsorption capacity of oxygen‐containing intermediates on FeN4 sites, and thus accelerating the ORR kinetic. This work offers an effective approach to constructing coupling catalysts that have single atoms coexisting with nanoclusters/nanoparticles for efficient ORR catalysis.

Preparation of Co[sbnd]N co-doped carbon nanosheets electrocatalyst for efficient oxygen reduction reaction in zinc-air battery

It is very vital that there be a high-activity and serviceable catalyst for the oxygen reduction reaction (ORR) in the Zn-air Battery. Herein, utilizing g-C3N4 as a self-sacrifice template and Cobalt-His framework as the precursor, a simple strategy was developed to synthesize Co/N co-doped carbon nanosheets (CoNC 800) as a metal electrocatalyst for ORR. Due to the Co/N co-doped CoNX site and large specific surface area, the acquired materials show a preeminent ORR catalytic activity with an initial potential (~0.96 V) and half-wave potential (E1/2) of 0.85 V (vs. RHE) in an alkaline medium. Most importantly, the material has superior long-term stability and methanol tolerance than Pt/C. Furthermore, we assembled the Zn-air battery employing catalyst as an air cathode catalyst, demonstrating maximum power densities of 144 mWcm−2, a specific capacity of 821.50 Wh·kg−1, and charge/discharge cycle stability of more than 140 h. The nanosheet structure electrocatalysts derived from the Cobalt-His framework and g-C3N4 provide an innovative and instructive approach to the design of diverse nanomaterials.

Strontium doped Fe-based porous carbon for highly efficient electrocatalytic ORR and MOR reactions

The catalytic activity improvement of Fe-based active sites derived from metal organic frameworks toward oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) remains a major challenge. In this study, the growth of strontium decorated 2-methylimidazole zinc salt (Sr/ZIF-8) is prepared as a carrier to vapor deposited iron formation Sr doped Fe-based nitrogen-doped carbon framework (named as Sr/FeNC). After high-temperature pyrolysis and vapor deposition, strontium carbonate nanocrystals are evenly dispersed on the shrunk dodecahedron carbon frame and multitudinous Fe-based active catalytic sites are embedded in carbon skeleton. The optimal Sr/FeNC-2 catalyst demonstrates the outstanding ORR performance in terms of a half-wave potential of 0.851 V and an onset potential of 0.90 V, while Sr/FeNC-2 exhibits a high current density of 18.2 mA cm−2 and a lower Tafel slope of 21 mV dec-1 in MOR. The exceptional catalytic activity could be ascribed to the synergistic coupling effect of strontium compounds with Fe-based catalytic sites (Fe-Nx, Fe, and iron oxide). In particular, the formation of SrCO3 affects the bonding configuration of the iron species sites, leading to an optimization of the electronic structure within the multihole carbon matrix. The synthetic approach presents a prospective strategy for future endeavors in developing innovative and advanced bifunctional catalysts for ORR and MOR.

Increasing the bifunctional OER/ORR activity of 3d transition metals doped g-C3N3 by controlling the charge states

Pursuing efficient bifunctional oxygen reduction reaction/ oxygen evolution reaction (OER/ORR) electrocatalysts is crucial for realizing sustainable and renewable clean energy, yet it remains a formidable challenge. In this study, we employ density functional theory and machine learning (ML) predictions to systematically investigate the bifunctional OER/ORR activity of 3d transition metal (TM) atom-doped g-C3N3. Our findings reveal that N-rich and C-poor growth conditions can facilitate 3d TM doping into g-C3N3. The Ni occupation N in 0 (Ni×N@C54N53, including 54 C and 53 N atoms), Ni occupation N in +1 (Ni•N@C54N53) and Ni interstitial sites in +1 charge state (Ni•int@C54N54, including 54 C and 54 N atoms) meet the requirements of bifunctional OER/ORR electrocatalysts, which because they (1) have lower formation energies, and (2) lower overpotentials (smaller than 0.47V), (3) can maintain stability under 300K and (4) their band gaps are decreased, which leads to facilitating electron transfer. ML predictions identify the 3d band center (εd) and the number of 3d electrons (Ne) as the most effective descriptors for overpotentials of OER and ORR, respectively. This work can pave the way for understanding the origin of bifunctional OER/ORR activity of 3d-TM doped g-C3N3 and benefit the rational design of novel electrocatalysts for other catalytic reactions by considering the charge states.

N,S-codoped carbon microporous structures derived from dead ginkgo leaves as efficient oxygen reduction reaction catalysts for Al–air batteries

The exploration and development of efficient and cost-effective oxygen reduction reaction (ORR) catalysts for non-metallic biomass have emerged as a crucial avenue for synthesizing diverse carbon nanomaterials.

Enhancing oxygen reduction activity of dinuclear copper complexes loaded on an N-doped carbon support via a low-temperature pyrolysis strategy.

Bioinspired by the active sites of multicopper oxidases (MCOs), bi/multinuclear copper complexes have attracted great attention in promoting catalytic activity for the oxygen reduction reaction (ORR). Herein, we report the preparation of a Cu-N-C electrocatalyst Cu-BPOZ@CNB-400 for efficient ORR, which was obtained by low temperature pyrolysis of a dinuclear 2,5-bis(2-pyridyl)-1,3,4-oxadiazole (BPOZ) copper complex loaded on a N-doped carbon support at 400 °C. Cu-BPOZ@CNB-400 exhibited a half-wave potential (E1/2) of 0.86 V vs. RHE for the ORR in 0.1 M KOH solution, which was significantly higher than that of the Cu-BPOZ@CNB-800 (E1/2 = 0.83 V) catalyst treated under high temperature (at 800 °C) and the control catalyst Cu-Phen@CNB-400 (E1/2 = 0.82 V) derived from low-temperature-treatment (at 400 °C) of a mononuclear phenanthroline-coordinated-Cu complex loaded on a N-doped carbon support. When Cu-BPOZ@CNB-400 was applied as the cathode catalyst in zinc-air batteries a maximum power density (Pmax) of 127 mW cm-2 could be achieved, demonstrating comparable catalyst performance to the commercial 20 wt% Pt/C (Pmax = 122 mW cm-2) and the control Cu-Phen@CNB-400 catalyst (Pmax = 105 mW cm-2) under similar experimental conditions. Low-temperature pyrolysis of dinuclear copper complexes on a carbon support improved the charge transfer efficiency, inhibited metal aggregation, and could produce highly dispersed Cu-N-C catalysts with dinuclear copper sites for promoting the 4e--reduction selectivity of the ORR. It thus provides a cost-effective approach for the controllable fabrication of efficient ORR catalysts to be applied for energy conversion devices.

Bifunctional diatomic site catalysts supported by β12-borophene for efficient oxygen evolution and reduction reactions.

Efficient bifunctional catalysts for oxygen evolution and reduction reactions (OERs/ORRs) are of great importance for sustainable and renewable clean energy, especially for metal-air batteries. Herein, we investigated β12-borophene with double-hole sites capped with 3d transition metal atoms to explore its catalyst performance for hydrogen evolution reactions (HERs), OERs and ORRs. It was found that the borophene is a good platform for diatomic site catalysts (DASCs) due to their advantage of stability over the corresponding single-atom catalysts (SACs) or clusters. The HER performance of DASCs on β12-BM was further improved compared to the SAC case. Furthermore, the supported FeNi DASC exhibited good catalytic performance for both OERs and ORRs, the overpotentials for which were 0.43 and 0.55 V, respectively, better than those of the corresponding supported Ni or Fe SAC due to synergistic effects. We herein propose a novel descriptor involving the Bader charges of coordinated atoms explicitly, behaving much better than the d-band center and integrated crystal orbital Hamilton population (-ICOHP) for DASCs. The synergistic effect of Fe-Ni pairs balanced the too strong binding of OH and further activated OH to achieve better catalytic performance. The results of this study can provide theoretical guidance for the design of efficient bifunctional electrocatalysts.

Hierarchical mesoporous N-doped carbon as efficient ORR/OER bifunctional electrocatalyst for rechargeable zinc-air battery

The construction of efficient oxygen reduction and oxygen evolution reaction (ORR/OER) bifunctional electrocatalysts is crucial for promising rechargeable Zinc-air batteries. Hierarchical mesoporous N doped carbon structures (HMNC) with superior catalytic...

Bifunctional oxygen reduction/evolution reaction electrocatalysts achieved by axial ligand modulation on two-dimensional porphyrin frameworks.

Exploring efficient and low-cost oxygen reduction and oxygen evolution reaction (ORR/OER) bifunctional catalysts is essential for the development of energy storage and conversion devices. Herein, enlightened by the experimentally synthesized cobalt(II) meso-tetraethynylporphyrins (Co-TEP) molecule, we designed a novel 2D covalent organic framework (COF), namely a 2D Co-TEP monolayer, by dimensional expansion. The 2D Co-TEP monolayer, with Co atoms distributed separately and stabilized by uniform pyrrolic-N coordination, features metal-nitrogen-carbon single-atom catalyst activity and shows tunable catalytic activity for the electrochemical ORR/OER by axial ligand (O, OH, Cl, CN, CH3, NO, F) modulation. By means of the state-of-the-art constant-potential first-principles computations and microkinetic simulations, we demonstrated that 2D Co-TEP-CN exhibits good ORR/OER performance in both acidic and alkaline conditions. The difference between the onset-potential for the OER and the half-wave potential for the ORR is only 0.85 V at pH = 1, smaller than that of Pt/IrO2 electrocatalysts. The good electrocatalytic performance is maintained by replacing the center metal atoms with Mn, Fe and/or Ni. Our investigation highlights the role of the pyrrolic-N coordination and the ligands in improving the catalytic activity of 2D COFs and provides new insights into the rational design of efficient bifunctional ORR/OER catalysts.

Small-size and well-dispersed Fe nanoparticles embedded in carbon rods for efficient oxygen reduction reaction.

The preparation of ultra-small and well-dispersed metal nanoparticles (NPs) is of great importance for promoting oxygen reduction. Here, a metal (Fe and Zn) NP (7 nm) based catalyst derived from a Zn-based metal-organic framework was obtained by a vapor adsorption strategy, demonstrating a high half-wave potential (0.868 V) and power density (196 mW cm-2).

Transition metals anchored on nitrogen-doped graphdiyne for an efficient oxygen reduction reaction: a DFT study.

The search for highly active and low-cost single-atom catalysts for the oxygen reduction reaction (ORR) is essential for the widespread application of proton exchange membrane fuel cells. Transition metals anchored on nitrogen-doped graphdiyne (GDY) have attracted considerable interest as potentially excellent catalysts for the ORR. However, the relationship between the active site and nitrogen-doped GDY remains unclear. In this work, we conducted a systematic investigation of sp-hybridized N atoms anchoring single transition metal atoms of 3d and 4d on GDY (TMC2N2) as electrocatalysts for the ORR. Firstly, 18 kinds of TMC2N2 were determined to have good thermodynamic stability. Due to the extremely strong adsorption of *OH, TMC2N2 exhibits inferior ORR performance compared to traditional Pt(111). Considering that *OH adsorption hinders the catalytic activity of TMC2N2, we modified the OH ligand of TMC2N2 to develop the high-valent metal complex (TMC2N2-OH) aiming to enhance the electrocatalytic activity. The adsorption of intermediates on most TMC2N2-OH is weakened after the modification of the OH ligand, especially for the adsorption of *OH. Thus, by comparing the ORR overpotential of catalysts before and after ligand modification, we find that the catalytic activity of different TMC2N2-OHs improves to various degrees. MnC2N2-OH, TMC2N2-OH, and TcC2N2-OH exhibit relatively high ORR catalytic activity, with overpotentials of 0.93 V, 1.19 V, and 0.92 V, respectively. Furthermore, we investigated the cause of improved catalytic activity of TMC2N2-OH and found that the modified coordination environment of the catalyst led to adjusted adsorption of ORR intermediates. In summary, our work sheds light on the relationship between nitrogen-doped GDY and transition metal sites, thus contributing to the development of more efficient catalysts.

Integrating multiple regulatory strategies: phase, morphology and interface engineering to construct a hierarchical Ni2P–MoS2/rGO heterostructure catalyst for efficient oxygen reduction reaction

Two-dimensional (2D) molybdenum disulfide (MoS2) with a large surface area and unique electronic properties has emerged as a promising noble metal-free catalyst for electrochemical energy storage/conversion applications.

Topotactic N-doped carbon for efficient oxygen reduction reaction

A topotactic molecular doping strategy is developed via in situ coupling of dechlorinated carbon with ringed heterocyclic molecules under mild conditions.

Donor–acceptor iron phthalocyanine-based hyper-crosslinked polymers with a modulated electronic structure for efficient oxygen reduction reaction in aluminum–air batteries

Poly-FePc-based HCPs with TTF modification are constructed and applied as ORR catalyst for Al–air batteries. The donor–acceptor structure was incorporated into poly-FePc-HCP to achieve structural and electronic regulation.