ORR Catalysts Research Articles

Catalysts for ORR Based on Silver-Modified Graphene Oxide and Carbon Nanotubes

The main obstacle to the widespread dissemination of fuel cells is the high cost, so researchers are actively searching for ways to replace the expensive platinum catalyst with cheaper analogs. In this paper we studied the Ag- and Pd-containing carbon catalysts based on carbon nanotubes and graphene oxide. The study of the textural characteristics of the catalysts showed that the greatest specific surface area has a catalyst based on MWCNT containing 10% silver, all synthesized catalysts are mainly mesoporous, and the content of micropores is insignificant. Raman spectroscopy and SEM data indicate a significant change in the structure of the modified carriers compared to pure MWCNT and GO. An electrochemical experiment was performed and linear voltammetric diagrams were obtained and compared with the voltammetric diagrams obtained on the platinum catalyst. GO_Ag 10% and MWCNT_Ag 10% Pd 10% are closest in the values of kinetic parameters in both kinetic and diffusion regions. GO_Ag 10% has the highest initial potential Eonset = −0.145 V and MWCNT_Ag 10% Pd 10% has the highest half-wave potential E½ = −0.23 V. The studied catalysts have characteristics comparable to those presented in the literature.

Hierarchical porous VN/NC/C nanocomposites with synergistic coupling for oxygen reduction

Vanadium nitride (VN) with high theoretical specific capacity and electrical conductivity is promising for application in Zn-air batteries. However, the agglomeration phenomenon during the synthesis of VN nanoparticles resulted in poor catalytic activity. Therefore, a highly efficient and durable ORR catalyst that vanadium nitride nanoparticles supported on nitrogen-doped carbon (VN/NC/C) was prepared by a self-assembly. Benefiting from the synergistic effect of VN and NC as well as its large specific surface area, porous structure, abundant pyridine N and graphitic N, the VN/NC/C nanocomposites exhibits excellent catalytic activity with Eonset of 0.87 V, a limiting current density of 4.05 mA·cm−2, and good stability. The experimental results and DFT calculations show that benefiting from the synergistic effect of NC and VN, the free energies of the reaction intermediates are optimized to significantly accelerate the O2 adsorption and reduce the potential of the rate-determining step. The Zn-air battery assembled with VN/NC/C nanocomposites exhibits an open circuit potential of 1.30 V, high power density of 141.82 mW∙cm−2 and an energy density of 856.27 Wh·kgZn-1. This work demonstrates the importance of the synergistic effect of NC and VN in the development of high-performance Zn-air batteries.

Carbon‐Based Electrocatalysts for Acidic Oxygen Reduction Reaction

AbstractOxygen reduction reaction (ORR) is vital for clean and renewable energy technologies, which require no fossil fuel but catalysts. Platinum (Pt) is the best‐known catalyst for ORR. However, its high cost and scarcity have severely hindered renewable energy devices (e.g., fuel cells) for large‐scale applications. Recent breakthroughs in carbon‐based metal‐free electrochemical catalysts (C‐MFECs) show great potential for earth‐abundant carbon materials as low‐cost metal‐free electrocatalysts towards ORR in acidic media. This article provides a focused, but critical review on C‐MFECs for ORR in acidic media with an emphasis on advances in the structure design and synthesis, fundamental understanding of the structure‐property relationship and electrocatalytic mechanisms, and their applications in proton exchange membrane fuel cells. Current challenges and future perspectives in this emerging field are also discussed.

Facile Preparation of Metallic Sites Anchored Nanocarbon Materials for Electrocatalysis

AbstractHerein, a novel method, heat mechanochemical synthesis (HMCS), is reported for facile and scalable preparation of electrocatalysts with metallic sites anchored on carbon materials. The method simultaneously provides mechanical energy and heat to drive reaction, by which target metal atoms are efficiently trapped in N‐doped and defect‐rich carbon that prepared in advance (NC). The advantages of this method are: (1) high contents of metals at the outermost surface; (2) unique metal sites formed under collisions with mechanical energy; and (3) not annealed at high temperatures, which would retain some unique active sites on the materials. A series of unitary transition metal (Cr, Mn, Fe, Co, Ni, Cu, or Zn) superficially anchored carbons are obtained via the HMCS. More than this, it is quite convenient to prepare multiple metals, such as combinations among these metals, highly dispersed and anchored on the carbon materials in one time. As a representative, the as‐prepared Fe‐NC (denoted as FeNCHM in context) is investigated in detail as catalyst for ORR and Zn‐air battery applications. The authors envision that the method of HMCS provides a good support of surface engineering for preparation of metals sites containing carbon at large scale.

Toward More Efficient Carbon-Based Electrocatalysts for Hydrogen Peroxide Synthesis: Roles of Cobalt and Carbon Defects in Two-Electron ORR Catalysis

Electrochemical production of H2O2 is a cost-effective and environmentally friendly alternative to the anthraquinone-based processes. Metal-doped carbon-based catalysts are commonly used for 2-electron oxygen reduction reaction (2e-ORR) due to their high selectivity. However, the exact roles of metals and carbon defects on ORR catalysts for H2O2 production remain unclear. Herein, by varying the Co loading in the pyrolysis precursor, a Co-N/O-C catalyst with Faradaic efficiency greater than 90% in alkaline electrolyte was obtained. Detailed studies revealed that the active sites in the Co-N/O-C catalysts for 2e-ORR were carbon atoms in C-O-C groups at defect sites. The direct contribution of cobalt single atom sites and metallic Co for the 2e-ORR performance was negligible. However, Co plays an important role in the pyrolytic synthesis of a catalyst by catalyzing carbon graphitization, tuning the formation of defects and oxygen functional groups, and controlling O and N concentrations, thereby indirectly enhancing 2e-ORR performance.

Recent Progress of Non-Pt Catalysts for Oxygen Reduction Reaction in Fuel Cells

In recent years, non-Pt-based ORR catalysts have been developing rapidly and have achieved performance comparable to or even surpassing Pt precious metal catalysts in specific reactions, offering new possibilities for Pt-based catalyst replacement and showing great promise for application. This paper reviews the recent research progress of non-Pt-based fuel cell ORR catalysts. The latest research progress of non-Pt-based ORR SACs (including single metal active site ORR SACs, multi-metal active site ORR SACs, and non-Pt-based noble metal catalyst ORR SACs), non-metallic ORR catalysts, alloy-based ORR catalysts, high-entropy alloy ORR catalysts, and other non-Pt-based fuel cell ORR catalysts are presented in detail. This paper discusses in detail the synthesis methods, characterization means, optimization of performance, and application prospects of these non-Pt-based ORR catalysts. In addition, this review details the excellent performance of these catalysts in terms of compositional and structural controllability, electrical conductivity, and chemical stability, as well as their ability to exhibit ORR activity comparable to that of commercial Pt/C catalysts. This field is full of opportunities and challenges. In summary, non-Pt-based fuel cells show great potential in ORR. With the continuous improvement of preparation and characterization technologies, catalysts have broad application and market prospects. In addition, the development trend of non-precious metal fuel cell catalysts is reviewed.

Electrochemical Activation and Its Prolonged Effect on the Durability of Bimetallic Pt-Based Electrocatalysts for PEMFCs

The present study, concerned with high-performance ORR catalysts, may be a valuable resource for a wide range of researchers within the fields of nanomaterials, electrocatalysis, and hydrogen energy. The objects of the research are electrocatalysts based on platinum–copper nanoparticles with onion-like and solid-solution structures. To evaluate the functional characteristics of the catalysts, the XRD, XRF, TEM, HAADF-STEM, and EDX methods, as well as the voltammetry method on a rotating disk electrode have been used. This work draws the attention of researchers to the significance of applying a protocol of electrochemically activating bimetallic catalysts in terms of the study of their functional characteristics on the rotating disk electrode. The choice of the potential range during the pre-cycling stage has been shown to play a crucial role in maintaining the durability of the catalysts. The activation of the PtCu/C catalyst during cycling of up to 1.0 V allows for an increase in the durability of the catalysts with onion-like and solid-solution structures of nanoparticles by 28% and 23%, respectively, as compared with activation of up to 1.2 V.

Electronic Configuration Regulation by N‐Doped MXenes Boosting Electrocatalytic Performance of Cobalt Phthalocyanine

AbstractThe precise control of electronic configurations of catalytic sites via molecular engineering is significantly desirable for boosting electrocatalytic activity. We reported a new‐type composite electrocatalyst with cobalt phthalocyanine supported on N‐doped MXene nanosheets (N‐MXene/CoPc) through a self‐assembly process. Beneficial from the joint action of N sites participation and axial coordination, N‐MXene/CoPc exhibits a high ORR activity with positive onset potential (Eonset=0.98 V vs. RHE) and half‐wave potential (E1/2=0.863 V), which is superior over the pristine CoPc (E1/2=0.72 V) and the composite with undoped MXene as support (MXene/CoPc, E1/2=0.771 V). Additionally, N‐MXene/CoPc exhibits an excellent durability with only 8.5 % attenuation after 25000 s of continuous i‐t test, while a more obvious decay 18.6 % for 20 wt.% Pt/C. This work not merely reported a robust ORR catalyst, but more provides a reasonable design strategy for nonnoble‐metal catalysts through catalyst‐support interactions.

Recent progress in heteroatom doping to modulate the coordination environment of M–N–C catalysts for the oxygen reduction reaction

This review focuses on the effects of heteroatom doping on the coordination configuration and electronic structure of M–N–C catalysts for ORR from three aspects: coordinated atoms, environmental atoms, and axial coordinated atoms.

Metal–organic frameworks for the photocatalytic oxygen reduction reaction to hydrogen peroxide

We detail the production process of H2O2 involving mechanisms, detection methods, and performance evaluation, and also summarize and predict the modifying ways of MOF catalysts for the photocatalytic ORR to H2O2, incorporating the challenges faced.

The pronounced effect of cobalt oxide on the electrocatalytic activity of palladium nanoparticles anchored on CoOx/NC towards the ORR with increased MA and ECSA

Pd@CoOx/NC1 as a cathode catalyst for ORR in PEMFC.

Two-dimensional metal-organic frameworks as bifunctional electrocatalysts for the oxygen evolution reaction and oxygen reduction reaction (OER/ORR): a theoretical study.

Effective bifunctional catalysts are needed for the two main processes in metal-air batteries (oxygen evolution reaction and oxygen reduction reaction (OER/ORR)) to increase efficiency. Herein, we systematically investigate the stability, electronic structure, and catalytic performance of the OER/ORR of two-dimensional (2D) conducting metal-organic frameworks (MOFs) M3(C6Se6)2 (M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Ir, and Pt) by first-principles calculations. The results show that Co3(C6Se6)2 has an overpotential of 0.51 V and 0.3 V for the OER and ORR, respectively, and Rh3(C6Se6)2 has an overpotential of 0.53 V and 0.29 V for the OER and ORR, respectively, which are very promising bifunctional catalysts. In addition, Ir3(C6Se6)2 is a very promising ORR catalyst with a low overpotential of 0.34 V. Volcano plots and contour maps of OER/ORR activity versus intermediate adsorption strength were established to describe the activity trend of M3(C6Se6)2 based on the relationship of adsorbed intermediates. Furthermore, the d-band center theory and crystal orbital Hamilton populations (COHPs) were used to relate the OER/ORR activity to the d-electrons of the central metal. Our study not only provides a novel bifunctional electrocatalyst but also provides some references for other 2D MOFs as electrocatalysts.

Structural design of FeCo alloy implanted into N,S co-doped carbon nanotubes via self-catalyzed growth for advanced liquid and flexible all-state-state Zn-air battery.

The introduction of transition bimetallic alloys can effectively improve oxygen reduction reaction (ORR) activity. However, the alloy particles are inclined to dissolve under harsher conditions, resulting in a serious decrease in catalytic activity and stability. Herein, an efficient ORR catalyst, FeCo alloy nanoparticles (NPs) encapsulated in N,S co-doped carbon nanotubes (FeCo10-NSCNTs), was developed through a self-catalyzed growth strategy. Due to the delicate structural design, the N,S co-doped structure can effectively improve the ORR performance by modulating the electronic properties and surface polarity of the carbon substrate, and the randomly connected carbon nanotube structure with large specific surface area can further enhance the adsorption and dissociation of gas molecules, accelerating the kinetics of gas participation in the reaction. Carbon-encapsulated FeCo alloys are beneficial for improving catalytic activity and durability. The FeCo10-NSCNTs displayed excellent ORR activity with a half-wave potential of E1/2 = 0.84 V and robust stability of 13 k cycles. More impressively, the assembled liquid-state Zn-air battery (ZAB) with FeCo10-NSCNTs as the air-electrode delivers an output power density of 146.68 mW cm-2 along with excellent operation durability. The assembled all-solid ZAB has good cyclic stability under 0-180° bending conditions. The synthesized N,S co-doping, carbon nanotubes and FeCo alloys provide important guidance for the construction of cheap non-noble metal-carbon hybrid nanomaterials.

S/N codoped carbon nanotubes as an efficient ORR electrocatalyst for zinc–air batteries

An S/N codoped carbon nanotube was prepared as an efficient ORR catalyst, and its performance is almost comparable to that of commercial Pt/C.

General synthesis of carbon-guarded cobalt-based nanospheres for oxygen reduction electrocatalysis

We construct carbon-guarded cobalt-based nanospheres composed of metal nanoparticles encased in a nitrogen doped carbon shell (M@NC NP), as efficient ORR catalysts.

Biochar electrode from banana peduncle as heteroatom doped ORR catalyst

Biochar electrode from banana peduncle as heteroatom doped ORR catalyst

Thienylene combined with pyridylene through planar triazine networks for applications as organic oxygen reduction reaction electrocatalysts.

Covalent triazine networks are interesting candidates for organic electrocatalytic materials due to their tunable, durable and sustainable nature. However, the limited availability of molecular designs that ensure both two-dimensionality and functional groups in the π-conjugated plane has hindered their development. In this work, a layered triazine network composed of thiophene and pyridine ring was synthesized by the novel mild liquid phase condition. The resulting network showed layered nature since its intramolecular interaction stabilized its planar conformation. The connection on the 2-position of the heteroaromatic ring prevents steric hindrance. The simple acid treatment method could be used to exfoliate the networks, resulting in high yields of nanosheets. The planar triazine network showed superior electrocatalytic properties for the oxygen reduction reaction in the structure-defined covalent organic networks.

Regulation of graphitized pore structure adjacent to atomic Fe[sbnd]N4 sites with pyrolyzing rate for highly active oxygen reduction reaction electrocatalysts

Non-noble metal monatomic ORR catalysts supported on carbon materials have drawn extensive attention for their maximum atomic activity utilization and high electrocatalytic efficiency. The pore structure of carbon carriers and rational design of efficient active sites are still one of the most serious challenges. Here, by regulating the graphitization of the pores surrounding FeN4 sites with a rapid pyrolyzing rate, we synthesized a nanosheet Fe-N4@graphitized porous carbon catalyst (Fe-N4@GPC) that exhibits higher ORR activity (E1/2 of 0.891 V) and cyclic stability (5000 cycle decay 11 mV) than commercial Pt/C catalyst in alkaline electrolyte. In addition, the assembled primary zinc-air battery has a superior performance (open circuit potential of 1.47 V and power density of 205.7 mW cm−2) than Pt/C catalyst (1.45 V, 199.6 mW cm−2). Compared with the FeN4 catalyst fabricated at a regular pyrolyzing rate, Fe-N4@GPC feature isolated FeN4 active sites surrounded by rich graphitized pores on nanosheets, which facilitates the electron and molecular-ionic transfer and thereby promoting the ORR performance. Therefore, this study highlights the significance of pyrolyzing rate regulation in modulating the graphitization of pores adjacent to the FeN4 active sites, which contributes to developing rational design and synthesis of efficient carbon-based monatomic catalysts in the future.

Co on porous carbon network derived from ZIF-8 for oxygen reduction and evolution reaction in alkaline solution

Porous carbon wrapped on cobalt catalyst is one of the promising candidates to replace noble metal-based catalysts for ORR. Herein, a porous carbon network (PCN) was obtained by synthesis of zeolitic-imidazole frameworks (ZIF-8) followed by pyrolysis at 1050 ℃ under a nitrogenous atmosphere and the cobalt (Co) was deposited on PCN to obtain Co-PCN by sequential reduction method. The PCN showed a relatively high specific surface area of 806.43 m2/g and decreases to 329.4 m2/g with the introduction of Co contents in PCN. The Co-PCN reveals excellent performance having a current density of 350 mA cm−2 for the ORR at 0.5 V after 20th cycles as a cathode material in rechargeable zinc-air batteries.

Trace Mn-doped on highly dispersed Fe/Mn-SNC ultrathin carbon nanosheets for efficient oxygen reduction reaction

The design and development of non-noble metal carbon-based catalysts with efficient oxygen reduction activity remains a difficult problem. Here, Ultrathin two-dimensional carbon nano sheet catalyst Fe/Mn-SNC with rich pore structure doped with trace manganese was synthesized by simple sodium chloride template cracking method and freeze-drying method. Citric acid containing a large number of OH and COOH groups can provide multiple coordination sites for metal ions. In 0.1 M KOH solution, the Fe/Mn-SNC catalyst performed better than Pt/C in terms of ORR performance (E1/2 was 0.920 V vs RHE) and endurance (E1/2 fell roughly 5 mV after 10,000 cycles). The reaction path of the Fe/Mn-SNC was calculated through DFT calculation. It was found that a small amount of Mn doping would reduce the adsorption energy of OH*, the last step in ORR reaction, which was conducive to OH* falling off from the catalyst surface, reducing the potential barrier required for the reaction, and improving its ORR activity. This research offers fresh perspectives on the development of enhanced energy conversion as well as the design and synthesis of high-performance ORR catalysts.