Efficient Electrocatalyst For Oxygen Reduction Reaction Research Articles

Ga‐Doped Intermetallic Pd3Pb Nanocubes as a Highly Efficient and Durable Oxygen Reduction Reaction Electrocatalyst

AbstractPd‐based nanocrystals are a promising candidate as non‐Pt electrocatalysts for oxygen reduction reaction (ORR), but their performance still has large room to be improved. Here, we have successfully synthesized Ga‐doped Pd3Pb nanocubes with different amounts of Ga by a simple one‐pot approach. When evaluated as electrocatalysts for ORR, the Ga‐doped Pd3Pb nanocubes exhibited substantially enhanced catalytic properties in an alkaline media relative to the Pd3Pb nanocubes and commercial Pt/C. Interestingly, the Ga‐doped Pd3Pb nanocubes showed a volcano‐like relationship in ORR activity as a function of the amount of Ga with the 1.76 % Ga‐doped Pd3Pb nanocubes (Pd3Pb/Ga‐2 NC) being the best ORR electrocatalysts. Specifically, the Pd3Pb/Ga‐2 NC/C exhibited the highest specific (7.57 mA cm−2) and mass activities (0.91 mA μgPd−1), which were 18.0 and 4.3 times higher than those of the commercial Pt/C. In addition, such Pd3Pb/Ga‐2 NC/C displayed the higher durability with an increase of 14.2 % in mass activity after 20000 cycles relative to commercial Pt/C (74.9 % loss). This enhancement in both activity and durability can be attributed to the strong hybridization interactions and the formation of Pd shells on the surface by leaching of Pb.

Carbon nanotubes-supported Ag/MoO2 or Ag/MnO2 heterostructures for a highly efficient oxygen reduction reaction

Supported by carbon materials and adjusting Ag surface states by metal oxides are two effective methods to promote the oxygen reduction reaction (ORR) performance of Ag-based catalysts. Herein, combining these two strategies, two kind of heterostructural electrocatalysts, carbon nanotubes-supported Ag/MoO2 (CNTs-Ag/MoO2) and carbon nanotubes-supported Ag/MnO2 (CNTs-Ag/MnO2) are constructed by facile two-step methods for the superior ORR catalytic activity in alkaline medium. Both CNTs-Ag/MoO2 and CNTs-Ag/MnO2 exhibit more positive onset potential and higher half-wave potential (~0.93 V and ~ 0.81 V (vs RHE) for CNTs-Ag/MoO2, ~0.99 V and ~ 0.86 V (vs RHE) for CNTs-Ag/MnO2), comparable and even superior to commercial Pt/C(~0.95 V and ~ 0.82 V(vs RHE)), which are benefit from Ag surface states regulation and the oxygen vacancy formation induced by the introduction of MoO2 or MnO2, as well as the enhanced electron transmission and dispersion of Ag/MoO2 or Ag/MnO2 resulted from the activated CNTs supporting. This work provides a useful reference to design efficient Ag-based ORR electrocatalysts with the superior performance.

Phase-Controlled Synthesis of Pd-Se Nanocrystals for Phase-Dependent Oxygen Reduction Catalysis.

Searching for highly efficient oxygen reduction reaction (ORR) electrocatalysts for fuel cell technology, in which the crystal structure plays a powerful role in regulating the electrocatalysis, is urgent yet challenging. Herein, we have explored the active and stable Pd-Se alloy electrocatalysts with controlled phase toward alkaline ORR. The phase-controlled Pd-Se nanoparticles (NPs) show interesting phase-dependent electrocatalytic performance, in which the Pd17Se15 NPs/C exhibits much better ORR performance than its counterpart, Pd7Se4 NPs/C, and the commercial Pd/C and Pt/C. Based on the detailed analysis, Pd in Pd17Se15 possesses more Se atom coordination and a higher valence state, thus providing a stronger capacity for the absorption of oxygenated species. DFT further reveals more charge transfer from the Pd17Se15 surface to the *OOH intermediate, which is the reason for the activity enhancement.

An efficient combination strategy for high-performance asymmetric-electrolyte metal–air batteries

Asymmetric-electrolyte metal–air batteries (AMABs) are the most promising technologies for realizing efficient energy conversion. However, the issues in cathode and separator parts seriously impede their practical applications. This article previews the latest finding on high-voltage AMABs with long cycle stability. Impressively, the generality of the developed approach is demonstrated by the AZnABs, ASiABs and ASnABs, exhibiting the enhanced operating voltage, power densities, and excellent rate performance.

Rational design of hierarchically porous Fe-N-doped carbon as efficient electrocatalyst for oxygen reduction reaction and Zn-air batteries

The rational design and construction of hierarchically porous nanostructure for oxygen reduction reaction (ORR) electrocatalysts is crucial to facilitate the exposure of accessible active sites and promote the mass/electron transfer under the gas-solid-liquid triple-phase condition. Herein, an ingenious method through the pyrolysis of creative polyvinylimidazole coordination with Zn/Fe salt precursors is developed to fabricate hierarchically porous Fe-N-doped carbon framework as efficient ORR electrocatalyst. The volatilization of Zn species combined with the nanoscale Kirkendall effect of Fe dopants during the pyrolysis build the hierarchical micro-, meso-, and macroporous nanostructure with a high specific surface area (1,586 m2·g−1), which provide sufficient exposed active sites and multiscale mass/charge transport channels. The optimized electrocatalyst exhibits superior ORR activity and robust stability in both alkaline and acidic electrolytes. The Zn-air battery fabricated by such attractive electrocatalyst as air cathode displays a higher peak power density than that of Pt/C-based Zn-air battery, suggesting the great potential of this electrocatalyst for Zn-air batteries.

Oxygen Reduction Electrocatalysts toward Practical Fuel Cells: Progress and Perspectives

AbstractFuel cells are an incredibly powerful renewable energy technology, but their broad applications remains lagging because of the high cost and poor reliability of cathodic electrocatalysts for the oxygen reduction reaction (ORR). This review focuses on the recent progress of ORR electrocatalysts in fuel cells. More importantly, it highlights the fundamental problems associated with the insufficient activity translation from rotating disk electrode to membrane electrode assembly in the fuel cells. Finally, for the atomic‐level in‐depth information on ORR catalysts in fuel cells, potential perspectives are suggested, including large‐scale preparation, unified assessment criteria, advanced interpretation techniques, advanced simulation and artificial intelligence. This review aims to provide valuable insights into the fundamental science and technical engineering for efficient ORR electrocatalysts in fuel cells.

Oxygen Reduction Electrocatalysts toward Practical Fuel Cells: Progress and Perspectives

AbstractFuel cells are an incredibly powerful renewable energy technology, but their broad applications remains lagging because of the high cost and poor reliability of cathodic electrocatalysts for the oxygen reduction reaction (ORR). This review focuses on the recent progress of ORR electrocatalysts in fuel cells. More importantly, it highlights the fundamental problems associated with the insufficient activity translation from rotating disk electrode to membrane electrode assembly in the fuel cells. Finally, for the atomic‐level in‐depth information on ORR catalysts in fuel cells, potential perspectives are suggested, including large‐scale preparation, unified assessment criteria, advanced interpretation techniques, advanced simulation and artificial intelligence. This review aims to provide valuable insights into the fundamental science and technical engineering for efficient ORR electrocatalysts in fuel cells.

Cobalt-nanoparticle impregnated nitrogen-doped porous carbon derived from Schiff-base polymer as excellent bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries

Designing transition metal and nitrogen co-doped carbon as efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional electrocatalysts is pivotal for rechargeable zinc-air batteries. Herein, a triazine-containing poly(Schiff-base) has been synthesized and used as the nitrogen-rich precursor to prepare Co/Co2N modified nitrogen-doped porous carbon (Co@NC). The formed cobalt nanoparticles are impregnated in the porous carbon matrix with an intermediary layer of catalytically active Co2N. Co@NC exhibits a specific surface area of 2513 m2 g−1 and remarkable bifunctional catalytic activities with a low gap of 0.76 V between ORR and OER overpotentials. The Co@NC-based battery possesses a peak power density of 141.6 mW cm−2, a specific capacity of 776 mAh g−1 and superior long-term cycling stability, stemmed from the unique impregnated structure with sufficient accessible active sites.

Co-Zn-MOFs Derived N-Doped Carbon Nanotubes with Crystalline Co Nanoparticles Embedded as Effective Oxygen Electrocatalysts.

The oxygen reduction reaction (ORR) is a crucial step in fuel cells and metal-air batteries. It is necessary to expand the range of efficient non-precious ORR electrocatalysts on account of the low abundance and high cost of Pt/C catalysts. Herein, we synthesized crystalline cobalt-embedded N-doped carbon nanotubes (Co@CNTs-T) via facile carbonization of Co/Zn metal-organic frameworks (MOFs) with dicyandiamide at different temperatures (t = 600, 700, 800, 900 °C). Co@CNTs- 800 possessed excellent ORR activities in alkaline electrolytes with a half wave potential of 0.846 V vs. RHE (Reversible Hydrogen Electrode), which was comparable to Pt/C. This three-dimensional network, formed by Co@CNTs-T, facilitated electron migration and ion diffusion during the ORR process. The carbon shell surrounding the Co nanoparticles resulted in Co@CNTs-800 being stable as an electrocatalyst. This work provides a new strategy to design efficient and low-cost oxygen catalysts.

Amorphous Fe nanoclusters embedded inside balloon-like N-doped hollow carbon for efficient electrocatalytic oxygen reduction

Rational designs of electrocatalytic active sites and architectures are of great importance to develop cost-efficient non-noble metal electrocatalysts towards efficient oxygen reduction reaction (ORR) for high-performance energy conversion and storage devices. In this work, active amorphous Fe-based nanoclusters (Fe NC) are elaborately embedded at the inner surface of balloonlike N-doped hollow carbon (Fe NC/Ch sphere) as an efficient ORR electrocatalyst with an ultrathin wall of about 10 nm. When evaluated for electrochemical performance, Fe NC/Ch sphere exhibits decent ORR activity with a diffusion-limited current density of ∼5.0 mA/cm2 and a half-wave potential of ∼0.81 V in alkaline solution, which is comparable with commercial Pt/C and superior to Fe nanoparticles supported on carbon sheet (Fe NP/C sheet) counterpart. The electrochemical analyses combined with electronic structure characterizations reveal that robust Fe−N interactions in amorphous Fe nanoclusters are helpful for the adsorption of surface oxygen-relative species, and the strong support effect of N-doped hollow carbon is benefitial for accelerating the interfacial electron transfer, which jointly contributes to improve ORR kinetics for Fe NC/Ch sphere.

Shape-tuned, surface-active and support-free silver oxygen reduction electrocatalyst enabled high performance fully non-PGM alkaline fuel cell.

Exploring non-platinum group metal (n-PGM) based efficient oxygen reduction reaction (ORR) electro-catalysts is highly important for realizing advancement in sustainable next generation-alkaline anion exchange membrane fuel cells (AAEMFCs). Herein, we demonstrate a new “hierarchical shape tuning approach” for the synthesis of controlled sized and shaped non-PGM based Ag ORR electro-catalysts with surface active nano-islands. Hierarchical shapes ranging from spherical (S-AgNs), worm-in-sphere, sphere-in-worm and vermiform (worm-like) Ag nanostructures (V-AgNs) were obtained by precisely varying the ratios of capping agent to dual reducing agents in water at ambient conditions. Compared to S-AgNs, V-AgNs revealed a higher mass normalized ORR Tafel activity (0.303 A mgAg−1 at 0.9 V), onset (1.06 V) and half wave (0.78 V) potentials and higher retention of limiting current density (>88%) after 5000 cycles in 0.5 M potassium hydroxide (KOH) solution attributable to their unique worm like morphology with surface active nano-islands and support free-nature enabled better catalyst utilization. In a fully “non-PGM AAEMFC” (n-PAAEMFC), V-AgNs exhibited the highest fuel cell activity of 115.6 mW cm−2 and stable short-term durability (∼240 h) compared to S-AgNs (41.3 mW cm−2) and previously reported fully n-PAAEMFCs indicating their potential use in next-generation alkaline fuel cells.

A defect-rich ultrathin MoS2/rGO nanosheet electrocatalyst for the oxygen reduction reaction.

The structural properties such as high specific surface area, good electrical conductivity, rich-defects of the catalyst surface guarantee outstanding catalytic performance and durability of oxygen reduction reaction (ORR) electrocatalysts. It is still a challenging task to construct ORR catalysts with excellent performance. Herein, we have reported column-like MoS2/rGO with defect-rich ultrathin nanosheets prepared by a convenient solvothermal method. The structure and composition of MoS2/rGO are systematically investigated. MoS2/rGO shows a remarkable electrocatalytic performance, which is characterized by an outstanding onset potential of 0.97 V, a half-wave potential of 0.83 V, noticeable methanol tolerance, and durability of 93.7% current retention, superior to commercial Pt/C. The ORR process occurring on MoS2/rGO is a typical four electron pathway. Therefore, this study achieves the design of a low-cost, highly efficient and stable nonprecious metal ORR electrocatalyst in alkaline media.

Cobalt Nanoparticles with Narrow Size Distribution Anchored to Flower-Like Carbon Microspheres for Enhanced Oxygen Reduction Catalysis

The development of efficient non-precious ORR electrocatalysts is crucial for the practical applications of fuel cells and metal-air batteries. In this work, a highly active and durable electrocatalyst for oxygen reduction reaction (ORR) was developed. Flower-like carbon microspheres coated with crystalline cobalt nanoparticles (Co@CMS) were successfully synthesized by the carbonization of Co-organic framework (Co-MOF). The Co nanoparticles, with narrow size distribution, are strongly anchored to the carbon support. Co@CMS possesses good catalytic ability for ORR in alkaline solution with a reduction peak potential ( E p, c ) of 0.75 V vs. RHE, which was comparable to Pt/C. The unique 3D porous structure of Co@CMS enhanced the electron transfer and electrolyte diffusion during the ORR. The ORR on Co@CMS is a diffusion-controlled process and follows a 4-electron-transfer mechanism.

Homogeneously supported PtGa NPs on nitrogen-doped mesoporous carbon as an enhanced ORR electro-catalyst

Platinum (Pt) nanoparticle catalysts show excellent performance for oxygen reduction reaction (ORR), but the high cost of Pt directly limits the commercialization of Pt-based catalysts. Supported PtGa alloy nanoparticles (NPs) with modified surface property and reactivity through ligand, strain and/or ensemble effects are considered as promising inexpensive low-Pt candidates. In this article, we report a PtGa nanoparticles with a size of 3.8 ± 0.4 nm anchored on nitrogen-doped mesoporous carbon (PtGa@NMC) for an efficient ORR electrocatalyst in alkaline electrolytes. The half-wave potential (E1/2) values of PtGa@NMC (0.92 V vs RHE) positively shift ~30 mV compared to commercial Pt/C in 1 M KOH solution. And it has outstanding long-term durability by the result of accelerated durability tests (ADTs) and chronoamperometry (CA). Considering high performance and excellent stability, PtGa@NMC presents the possibility of replacing contemporary Pt-based catalysts.

Well-dispersed ultrafine CoFe nanoalloy decorated N-doped hollow carbon microspheres for rechargeable/flexible Zn-air batteries

Metal-organic frameworks (MOFs) offer great advantages for construction of bimetallic alloys as efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts for rechargeable/flexible Zn-air batteries. Herein, a template-assisted method is developed to reduce the crystal size of CoFe-ZIF via in-situ growing on hollow polypyrrole spheres (h-PPy). As a result, the well-dispersed ultrafine CoFe nanoalloy were obtained with N-doped hollow carbon microspheres (N-HCSs) as support. Owing to the unique alloy structure with ultrafine size, uniform dispersion of the CoFe nanoalloy on the highly conductive N-HCSs support via strong interactions, the proposed CoFe/N-HCSs afford high catalytic activity and stability toward ORR. Interestingly, the CoFe/N-HCSs also deliver a low overpotential of 292 mV at 10 mA cm−2 for OER in alkaline electrolyte, demonstrating their superior bifunctional catalytic performance. Moreover, the CoFe/N-HCSs can endow the liquid Zn-air batteries with better energy density (882.3 Wh kgZn−1) and cycling stability than those of Pt/C catalyst and exhibit potential feasibility in all-solid-state Zn-air batteries.

Synthesis of MgNiO2/CoNC-Based Ternary Metallic Dual-Active Interfacial Porous Hollow Nanocages as Efficient Oxygen Reduction Reaction and Oxygen Evolution Reaction Bi-Functional Electrocatalysts

Combining the catalytic activities of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) into one electrocatalyst is of great significance in simultaneously prompting the charge-discharge cycles of various renewable energy storage and conversion systems such as metal-air batteries. Herein we report a ternary metallic based MgNiO2/CoNC porous hollow nanocage composite, which assembled with intimate contacted MgNiO2 and Co species to form the ultrathin nanocage shells and serve as the ORR and OER active components respectively to reveal a highly bi-functional catalytic performance. The possible synergy of each seamlessly connected metallic sites renders the hybrid material with excellent ORR and OER activities, which outperform than the corresponding benchmarks. Particularly, we speculate such efficient catalytic activity might arise from the synergistic chemical coupling effects within MgNiO2/CoNC and therefore, these results reveals promising prospects in developing multi-metallic composites toward efficient electrochemical energy devices.

Single Atoms on a Nitrogen-Doped Boron Phosphide Monolayer: A New Promising Bifunctional Electrocatalyst for ORR and OER.

Efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional electrocatalysts have been pursued for decades. Meanwhile, single metal atoms embedded in a two-dimensional material substrate (2D-substrate) have emerged as an outstanding catalyst. Herein, we report on computational ORR/OER efficiencies of a series of single atom catalyst systems, with a nitrogen-doped boron phosphide monolayer (N3-BP) as the 2D-substrate, and with Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Rh, Pd, Ir, and Pt as the single-atom subject (M). In brief, our density functional theory results show that the overpotentials for ORR/OER are low for CoN3-BP, NiN3-BP, and PtN3-BP, with {ηORR; ηOER} of {0.36; 0.42 V}, {0.29; 0.44 V}, and {0.32; 0.25 V}, respectively. The relevant attributes such as the chemical stability of the 2D-substrate in the ORR/OER environments, immobilization of the single-atom subject on the 2D-substrate, and mechanisms of the ORR/OER activity and the catalyst recovery on the MN3-BP catalysts were carefully examined. The key to the comparative study is how the electronic states of the reaction center near the Fermi level of the catalytic system match the frontier orbitals of ORR/OER reaction intermediates. In short, our method predicts the ORR/OER catalytic efficiencies of novel catalysts via a single-atom/2D-substrate design strategy.

Dual-active-sites design of CoNx anchored on zinc-coordinated nitrogen-codoped porous carbon with efficient oxygen catalysis for high-stable rechargeable zinc-air batteries

The sluggish kinetics of oxygen reduction reaction (ORR) is the bottleneck for practical applications of zinc-air batteries (ZABs). Developing highly efficient ORR electrocatalysts is of the essence for large-scale applications of ZABs. Herein, we design and synthesize the CoNx/Zn, N co-doped porous carbon structure (CoNx/Zn-NC) by self-polymerization of biomass materials and coupling of nitrogen-rich species with metallic ions. The introduced zinc element can regulate electronic structures of electrocatalysts and construct bimetallic active sites (N-Co/N-Zn species), facilitating the adsorption of reaction intermediates and further enhancing electrocatalytic performance. The porous carbon structure obtained by the self-polymerization of locust bean gum not only disperses active sites but also improves the O2 and electron transfer efficiency of electrocatalysts. The CoNx/Zn-NC exhibited excellent ORR electrocatalytic performance (E1/2 = 0.85 V) as well as outstanding stability. Impressively, the ZABs assembled with CoNx/Zn-NC demonstrated a high maximum power density, specific capacitance, and excellent charge/discharge cycling stability for 115 h, surpassing Pt/C catalyst.

Interface engineering of Co3Fe7-Fe3C heterostructure as an efficient oxygen reduction reaction electrocatalyst for aluminum-air batteries

Aluminum-air batteries with merits of high theoretical energy densities, low cost and environmental-friendliness are promising candidates for next-generation energy storage and conversion systems. Rational design of efficient heterogeneous catalysts for oxygen reduction reaction (ORR) in neutral and alkaline solutions is of great significance for aluminum-air batteries. Herein, an interface engineering strategy is proposed to realize Co3Fe7-Fe3C heterostructure with abundant interfaces anchored on 3D honeycomb-like N-doped carbon, which inherits the original structure of the biomass precursor. The as-prepared Co3Fe7-Fe3C heterostructure on honeycomb-like N-doped carbon (denoted as Co3Fe7-Fe3C/HNC) displays remarkable electrocatalytic activity and stability towards ORR in both alkaline and neutral solutions. It shows a very positive onset potential of 0.98 V and a half-wave potential of 0.90 V in 0.1 M KOH solution (Eonset = 0.78 V and E1/2 = 0.64 V in 3.5% NaCl solution) towards ORR. The high ORR performance is mainly ascribed to the abundant engineered interfaces, which can not only boost the intrinsic activity, but also guarantee fast charge transfer. The superior ORR performance is also supported by the density functional theory calculation. Moreover, the fabricated Al-air battery displays a larger working voltage and a higher power density compared with those of Pt/C. Furthermore, the Co3Fe7-Fe3C/HNC catalyst exhibits outstanding stability and durability during mechanical recharging and continuous discharging processes. This work demonstrates a new strategy to design and construct multifunctional catalysts with interfacial structure for high performance metal-air batteries.

Coexisting Single-Atomic Fe and Ni Sites on Hierarchically Ordered Porous Carbon as a Highly Efficient ORR Electrocatalyst.

The development of oxygen reduction reaction (ORR) electrocatalysts based on earth-abundant nonprecious materials is critically important for sustainable large-scale applications of fuel cells and metal-air batteries. Herein, a hetero-single-atom (h-SA) ORR electrocatalyst is presented, which has atomically dispersed Fe and Ni coanchored to a microsized nitrogen-doped graphitic carbon support with unique trimodal-porous structure configured by highly ordered macropores interconnected through mesopores. Extended X-ray absorption fine structure spectra confirm that Fe- and Ni-SAs are affixed to the carbon support via FeN4 and NiN4 coordination bonds. The resultant Fe/Ni h-SA electrocatalyst exhibits an outstanding ORR activity, outperforming SA electrocatalysts with only Fe- or Ni-SAs, and the benchmark Pt/C. The obtained experimental results indicate that the achieved outstanding ORR performance results from the synergetic enhancement induced by the coexisting FeN4 and NiN4 sites, and the superior mass-transfer capability promoted by the trimodal-porous-structured carbon support.