High-efficiency Oxygen Reduction Reaction Research Articles

Atomically dispersed manganese-based catalysts for efficient catalysis of oxygen reduction reaction

Rational design and preparation of earth-abundant materials with high-efficiency oxygen reduction reaction (ORR) performance is pivotal for fuel cells. Here, an atomically dispersed Mn- and nitrogen-codoped graphene material (Mn@NG) is developed by a facile high-temperature annealing and subsequent acid-leaching strategy. The atomically dispersion of manganese in Mn@NG is confirmed by aberration-corrected electron microscopy with atomic resolution and the main structure of MnN4 moiety is resolved by X-ray absorption spectroscopy. The Mn@NG catalyst shows an onset potential and half-wave potential of 0.95 and 0.82 V vs RHE in 0.1 M KOH solution, respectively. Theoretical calculations manifest that MnN4 moiety embedded into graphene is the active center for efficient ORR, on which the theoretical overpotential is 0.63 V, lower than that on graphitic-N (1.18 V), pyridinic-N (1.58 V), MnN3-G (1.48 V), MnN3O-G (2.33 V), and Mn3O4 (001) surface (0.86 V).

Carbon nanotube@ZIF–derived Fe-N-doped carbon electrocatalysts for oxygen reduction and evolution reactions

Iron-nitrogen co-doped hierarchical porous carbon (Fe-N-HPC) was synthesized through the carbonization of carbon nanotube@ZIF composite. It was found that the porous carbon structure with uniformly distributed active N-doping and Fe-N sites was conduced to oxygen adsorption, electronics, and mass transfer. In addition, the integrated electroconductive multi-walled carbon nanotube skeleton loaded with the porous carbon boosted the density and stability of reactive sites. As a result, the prior catalyst exhibited a high-efficiency oxygen reduction reaction (ORR) activity with a half-wave potential of − 0.078 V (vs. Ag/AgCl) positive than the commercial Pt/C (− 0.092 V). For oxygen evolution reaction (OER) performance, the potential was 0.732 V at the current density of 10 mA cm−2 compared with IrO2 (0.643 V). The presented strategy provided a method to design a bi-functional electrocatalyst with superior performance, prior stability, and favorable methanol tolerance.

A Single-Atom Iridium Heterogeneous Catalyst in Oxygen Reduction Reaction.

Combining the advantages of homogeneous and heterogeneous catalysts, single-atom catalysts (SACs) are bringing new opportunities to revolutionize ORR catalysis in terms of cost, activity and durability. However, the lack of high-performance SACs as well as the fundamental understanding of their unique catalytic mechanisms call for serious advances in this field. Herein, for the first time, we develop an Ir-N-C single-atom catalyst (Ir-SAC) which mimics homogeneous iridium porphyrins for high-efficiency ORR catalysis. In accordance with theoretical predictions, the as-developed Ir-SAC exhibits orders of magnitude higher ORR activity than iridium nanoparticles with a record-high turnover frequency (TOF) of 24.3 e- site-1 s-1 at 0.85 V vs. RHE) and an impressive mass activity of 12.2 A mg-1 Ir , which far outperforms the previously reported SACs and commercial Pt/C. Atomic structural characterizations and density functional theory calculations reveal that the high activity of Ir-SAC is attributed to the moderate adsorption energy of reaction intermediates on the mononuclear iridium ion coordinated with four nitrogen atom sites.

Ultrafine iron-cobalt nanoparticles embedded in nitrogen-doped porous carbon matrix for oxygen reduction reaction and zinc-air batteries

Oxygen reduction reaction (ORR) is a key process in renewable energy conversion and storage technologies, including fuel cells and metal-air batteries. Pt is a highly efficient ORR electrocatalyst, but its large-scale application is severely prohibited by the high cost. In the pursuit of cost-effective electrocatalysts, it is urgent to develop non-noble metal ORR catalysts. Herein, we report a facile strategy for synthesizing an ORR electrocatalyst based on ultrafine bimetallic FeCo nanoparticles (NPs) anchoring on N-doped porous carbon matrix (FeCo-NC). By optimizing the ratio of Fe and Co, the FeCo-NC-1 catalyst exhibits excellent performance for ORR with the half-wave potential of 0.84 V and limiting current density of −5.3 mA cm−2, which is comparable to the commercial Pt/C catalyst. When applied to Zn-air batteries, FeCo-NC-1 catalyst possesses a high open-circuit potential (1.50 V) and large specific capacity (726.2 mA h g−1) with a good long-term stability and methanol-tolerant capability, which are even superior to the commercial Pt/C catalyst. The first-principle calculations indicate the bimetallic FeCo-NC has stronger O2 adsorption than the single metal nitrogen-doped carbon catalysts (Fe-NC and Co-NC), which is the primary reason for the better ORR performance. We believe this work can be helpful for the development of inexpensive and high-efficient ORR electrocatalysts.

Design of high efficient oxygen reduction catalyst from the transition metal dimer phthalocyanine monolayer

Due to the large surface area, unique atomic configurations and dispersed metal sites, metal-organic porous monolayers provide a promising strategy for catalysis. Among them, the transition metal dimer phthalocyanine (TM2Pc) monolayer is one of the interesting members. Herein, we studied the oxygen reduction reaction (ORR) of TM2Pc with a series of transition metal dimers (M = Mn-Cu and Ru-Pd) by using the density functional theory. Volcano plot suggests that Fe2Pc has the best ORR activity. This is also confirmed by thermodynamic and kinetic study. Among the studied TM2Pc, Fe2Pc has the highest working potential of 0.98 V (smallest overpotential of 0.25 V), larger than 0.78 V for pure Pt. The energy barrier calculations show that for Fe2Pc, the rate-determining step is the *OOH hydrogenation to form *OH + *OH with an energy barrier of 0.25 eV, much smaller than 0.80 eV for pure Pt. Therefore, Fe2Pc has good ORR activity compared with pure Pt. These results also indicate that the introduction of transition metal dimer on phthalocyanine monolayer would provide a novel strategy for the design of high efficient ORR catalysts.

Polymerization-dissolution strategy to prepare Fe, N, S tri-doped carbon nanostructures for Zn-Air batteries

Heteroatom doped carbon based hierarchical nanostructures are one of most interesting electrode materials for boosting oxygen reduction reaction (ORR) owing to the active electronic structure and appealing structural stability. Herein we demonstrated a ‘polymerization-dissolution’ method to prepare a highly stable Fe, N, S tri-heteroatom doped core-shell carbon (HCSC) nanostructural ORR catalyst. The unique advantages, including the uniformly dispersed N, S and Fe–N active sites, and the special leaf-like core-shell nanostructure, endow the optimized HCSC catalyst (HCSC-IV-H) owning high-efficient ORR activity. Moreover, a Zn–air battery assembled with HCSC-IV-H exhibits a higher open potential (1.430 V) and lower discharge overpotential, comparing with the commercial IrO2 + 20% Pt/C catalyst. The present work highlights a novel strategy to construct highly efficient heteroatom doped nano-carbon materials for renewable energy storage and conversion devices.

Core@Shelled Co/CoO Embedded Nitrogen-Doped Carbon Nanosheets Coupled Graphene as Efficient Cathode Catalysts for Enhanced Oxygen Reduction Reaction in Microbial Fuel Cells

High-efficiency oxygen reduction reaction (ORR) catalysts are crucial for facilitating the large-scale exploitation of electrochemical energy storage and conversion technologies. Herein, we demonstrate a carbon-based metal hybrid, which offers a higher electrocatalytic activity than that of the individual composite by optimizing the electronic modulation effect from suitable microstructure. The resulting cobalt@cobalt oxide nanoparticles embedded in N-doped carbon shell couple with hierarchical porous graphene (GCN–Co@CoO), exhibiting a significantly enhanced ORR activity in alkaline solution and highlighting a synergistic effect between N-doped carbon shell and metallic Co species. More precisely, the GCN–Co@CoO hybrid pyrolyzed at 800 °C achieves a more positive half-wave potential of −0.194 V (vs SCE) and superior limiting current of 4.91 mA cm–2. Moreover, the GCN–Co@CoO composite also shows an outstanding tolerance to methanol crossover effects and long-term stability. Furthermore, based on the GCN–Co@CoO cathode catalyst, the self-assembled microbial fuel cells perform a maximum power density of 611 ± 9 mW m–2 at a high current density of 1869 ± 24 mA m–2.

Nanowire-Templated Synthesis of FeNx -Decorated Carbon Nanotubes as Highly Efficient, Universal-pH, Oxygen Reduction Reaction Catalysts.

It is of increasing importance to develop highly active and economical oxygen reduction reaction (ORR) electrocatalysts, which have great significance for the large-scale implementation of various energy conversion systems, including metal-air batteries and fuel cells. Herein, a novel method to synthesize FeNx -decorated carbon nanotubes as a high-efficiency ORR catalyst, by utilizing ZnO nanowires as a sacrificial template and a Fe-polydopamine complex as metal and carbon sources, is reported. The obtained catalyst shows great potential for replacing Pt/C as the ORR catalyst under various pH conditions, from alkaline to acidic electrolytes. The high conductivity, large surface area of the carbon nanotube, and highly active FeNx species contributed greatly to the high performance of the catalyst. The work presented herein paves a new way for the synthesis of 1D porous nanomaterials for a broad range of energy-related applications.

A comparative study of iron phthalocyanine electrocatalysts supported on different nanocarbons for oxygen reduction reaction

Developing non-platinum electrocatalyst with high performance and durability is strongly desired for the next-generation low-cost fuel cells. Here, we present a facile and scalable preparation method for the hybrid electrocatalysts of iron phthalocyanine (FePc) and seven different nanocarbons including carbon black (Vulcan and Ketjen black), carbon nanotubes, and mesoporous carbons. All the FePc/nanocarbon catalysts exhibited a higher activity for oxygen reduction reaction (ORR) than that of the commercial Pt/C, and the highest half-wave potential (0.918 V vs. RHE) ever reported in the literature was obtained from the composite catalyst of FePc and Ketjen black. Furthermore, the amount of electrochemically active sites (the centered iron ion of FePc) and turnover frequency of ORR on FePc were found to be respectively responsible for the electrocatalytic activities and long-term durability of the FePc/nanocarbon catalysts for ORR. We fabricated a MEA using FePc-KCB, anion electrolyte membrane and Pt/C as cathode, electrolyte membrane, and anode, respectively, and its power density in anionic medium reached 108 mW cm−2, which is higher than that of the conventional Pt/C catalyst. Such obtained results are important for the design of non-Pt based high efficient and durable ORR and fuel cell catalysts.

Localized micro-deflagration induced defect-rich N-doped nanocarbon shells for highly efficient oxygen reduction reaction

Defect engineering is capable of significantly enhancing catalytic performance of target materials, but very few high efficiency defect-engineered catalysts were reported due to the lacking of systematic and comprehensive understanding of defect effect, as well as controllable experimental practice. Here, we reported high-efficiency oxygen reduction reaction (ORR) nanocarbon shell electrocatalyst, using a unique localized micro-deflagration strategy combined with postprocessing of heat treatment. This micro-deflagration allows the ultrafast and large scale formation of highly porous nanocarbon structure with rich nitrogen doping, where parts of nitrogen can be further removed via post heat treatment for constituting targeted active sites of defects for ORR. The defective nanocarbon shells demonstrate large specific surface area (540 m2g-1) with 6.05 at% N-doping, which allows exceptional electrocatalytic activity (Eonset of 0.89 V vs.RHE, E1/2 of 0.79 V vs.RHE and Jk of 5.26 mA cm−2), long-term stability, and tolerance to crossover effect, comparable to commercial Pt/C in alkaline electrolyte. Most importantly, this localized micro-deflagration is significantly enriched the research of defect engineering chemical electrocatalyst, and great promising for the synthesis of other metal-free nanocarbon materials.

Novel hierarchically porous Ti-MOFs/nitrogen-doped graphene nanocomposite served as high efficient oxygen reduction reaction catalyst for fuel cells application

Novel hierarchically porous titanium-metal organic frameworks/nitrogen-doped graphene (Ti-MOFs/NG) nanocomposite derived from titanium-metal organic frameworks (Ti-MOFs) and the nitrogen-doped graphene (NG) has been originally synthesized successfully. Notably, the Ti-MOFs/NG nanocomposite has been for the first time investigated in detail, as oxygen reduction reaction (ORR) catalyst of cathodic materials for fuel cells. The results show that the Ti-MOFs/NG nanocomposite possesses excellent ORR performances, whether in alkaline or acidic medium, due to existences of the Ti3N2-x, C2O7Ti2.3, H2Ti5O11, Ti and TiO active ORR segments. Specifically, the onset potential (E0) and the Tafel slope value of the Ti-MOFs/NG nanocomposite are 1.14 V and 17.84 mV dec−1 in 0.1 M HClO4, respectively. Similarly, high ORR efficiency of the Ti-MOFs/NG nanocomposite also exhibit in alkaline medium. The relative current density can still keep 99.88% of the original value after 10800 s measurements in 0.1 M KOH. Additionally, small electrochemical impedance and excellent tolerance toward fuel molecules have been exhibited in both electrolytes. These ORR properties are superior to those of most of previously reported materials derived from other MOFs, in both alkaline and acidic media. Thus, the Ti-MOFs/NG nanocomposite is as a novel promising candidate for ORR catalyst to solve the main problems of sluggish reaction kinetics of the ORR, high cost of precious metal catalysts and low durability of the traditional catalysts, applied to fuel cells, metal-air batteries and further to water splitting in energy conversion and storage devices.

A novel synthesis of Prussian blue nanocubes/biomass-derived nitrogen-doped porous carbon composite as a high-efficiency oxygen reduction reaction catalyst

Exploring efficient non-platinum catalysts for the oxygen reduction reaction (ORR) instead of platinum-based catalysts is vital for reducing costs of fuel cells or metal-air batteries. A Prussian blue/N-doped porous carbon (PB/NPC) nanocomposite catalyst for ORR was synthesized by a novel method of one-step high-temperature pyrolyzing the mixture of the casein extracted with ferric ions, potassium hydroxide and melamine. The PB nanocubes were embedded in the NPC, and the particle size of PB nanocubes was less than 100 nm. The presence of PB effectively reduced the production of hydrogen peroxide, and the PB/NPC catalyst exhibited high catalytic activity such as more positive onset-potential (of ∼0.93 V vs. RHE), large diffusion limiting current density (5.79 mA cm−2) close to Pt/XC-72 (20%) catalyst and good stability in alkaline media due to the stable binding structure and the synergistic effect of PB nanocubes and NPC. The synthetic strategy of the PB/NPC provides a facile and effective method for the preparation of non-platinum catalysts for energy conversion and storage applications.

Designing iron carbide embedded isolated boron (B) and nitrogen (N) atoms co-doped porous carbon fibers networks with tiny amount of B[sbnd]N bonds as high-efficiency oxygen reduction reaction catalysts

In this paper, polyvinylpyrrolidone (PVP) and 4-hydroxybenzeneboronic acid (o-HPBA) are polarized in alkaline solution and then employed as boron (B) and nitrogen (N) sources. Fe(AC)2/o-HPBA/PVP/DMF(N,N-Dimethylformamide) slurries are first electrospunned into three-dimensional (3D) networks. Due to the electrostatic repulsion between negatively charged O− groups surrounding N and B atoms, N and B atoms can be kept far away from each other. Upon optimizing o-HPBA dosages, the maximum amount of isolated B and N atoms are successfully doped into the 3D porous iron carbide (Fe3C) embedded B and N co-doped carbon fibers (Fe3C@B1.0NPCFs) networks with tiny BN clusters. Electrochemical measure results demonstrate that Fe3C@B1.0NPCFs exhibit much better oxygen reduction reaction (ORR) activity than 20 wt% Pt/C in alkaline electrolyte. In acidic electrolyte, Fe3C@B1.0NPCFs also displays ORR activity comparable to Pt/C (its onset and half-wave potentials are just 40 and 50 mV more negative than those of Pt/C). Moreover, Fe3C@B1.0NPCFs show better stability and methanol tolerance ability than Pt/C for ORR in both alkaline and acidic solutions. This work opens new avenues for intentionally preventing the malignant combination of B and N atoms and boosting the electrocatalytic activity of B and N co-doped and Fe3C embedded carbon catalysts.

Manganese Oxide/Reduced Graphene Oxide Nanocomposite for High-Efficient Electrocatalyst towards Oxygen Reduction Reaction

Sluggish kinetics of oxygen reduction reaction (ORR) are the critical challenge for metal-air batteries and fuel cells. To increase the reaction rate, the high-efficient electrocatalysts are needed. Among various catalysts, platinum and its alloys are investigated as the best catalyst for the ORR. However, the use of Pt-based catalysts is still suffered from many disadvantages including excessive cost, scarcity, and poor stability. In this work, lithium-birnessite (Li-bir), reduced graphene oxide (rGO), and Li-bir/rGO nanocomposite were tested as the ORR catalysts. The linear sweep voltammogram (LSV) curves at a scan rate of 10 mV s-1 show that the Li-bir/rGO nanocomposite provides the best catalytic performance with an onset potential of 0.87 V vs. RHE, half-wave potential of 0.72 V vs. RHE, limiting current density of 5.72 mA٠cm-1 (at a rotation rate of 1600 rpm), along with the Tafel slope of 92.5 mV٠dec-1. Furthermore, the electron transfer number per oxygen molecule calculated by Koutechy–Levich (K–L) equation is 3.84, indicating a 4-electron pathway for the ORR suggesting that the Li-bir/rGO nanocomposite can be used as a high-efficient ORR catalyst. More interestingly, a current retention of the Li-bir/rGO nanocomposite remains over 84 % while the current density of the commercial Pt/C decreases to 67 % after 17,000 seconds. The catalyst in this work may be practically used in many applications such as metal-air batteries.

Pt0.61Ni/C for High-Efficiency Cathode of Fuel Cells with Superhigh Platinum Utilization

Exploring advanced electrocatalysts to accelerate the sluggish oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs) is a promising route to alleviate the current challenges of fossil fuel exhaustion and environment pollution. Herein, a carbon-supported highly dispersed PtNi nanocatalyst (Pt0.61Ni/C) with low platinum content of 2.76 wt % was prepared simply based on galvanic replacement for a high-efficiency ORR process. It presents a mass activity of ∼5 times of the conventional Pt-based catalyst at 0.9 V (vs reversible hydrogen electrode (RHE)) and a remarkable durability and methanol tolerance. The acidic fuel cell with such cathode catalyst (Pt0.61Ni/C) presents a striking performance with maximum power density up to 1.1 W cm–2 at 80 °C. Due to the extremely low platinum loading in the whole fuel cell, its Pt utilization (0.093 gPt kW–1) is the highest reported ever in H2/O2 fuel cells. Such impressive performance of Pt0.61Ni/C makes the obtained Pt0.61Ni/C catalyst a ve...

Platinum-Based PEMFC Electrodes – Can Electrodes with Low Pt Loading be Durable?

Proton exchange membrane fuel cells now present performances that enable their commercialization, as demonstrated by the recent release of fuel-cell powered vehicles (forklifts by Plug Power, FCEV Miraï by Toyota, etc.). The goal of PEMFC manufacturers is now to reduce the materials cost of their system and to enhance their durability/reliability, so that they can meet the market requirements. To that goal, highly-efficient oxygen reduction reaction (ORR) electrocatalysts have been developed recently [1-6], these materials mostly originating from the dealloying of PtM/C electrocatalysts (M = Ni, Cu, etc.) initially rich in M. Unfortunately, to date, the scientific community has failed to properly use these materials in an operating PEFMC: neither are their apparent performances approaching those expected from tailored data obtained in rotating disk electrode setup (Figure 1), nor are the materials presenting a sufficient durability in the operating conditions of a PEMFC (see for example [7]). In this tutorial, some reasons for our present incapacity to operate properly membrane electrode assemblies based on low-Pt-loading of highly-efficient Pt-based electrocatalysts will be discussed. In particular, it will be shown that the degradation mechanisms at stake for present (conventional) PtM/C electrocatalysts (coarsening of the nanoparticles, loss of their shape/texture, selective dissolution of the M element, corrosion of the carbon support, etc.) still operate (at least for some of them) for the advanced electrocatalysts. Besides, the inevitable leaching of the M element raises issues of pollution of the ionomer [8], which is particularly detrimental, not only to the proton conduction, but also to the mass-transport of oxygen to the active sites. In addition, as these electrocatalysts are more active, their optimized operation relies on an emphasized mass-transport of reactants (both H+ and O2) to the catalytic sites, which is not granted for present ionomers and MEA structure [9, 10].

Li-Birnessite Manganese Oxide Coated on Graphene Aerogel for High-Efficient Electrocatalyst Towards Oxygen Reduction Reaction

The sluggish kinetics of oxygen reduction reaction (ORR) is a critical challenge for metal-air batteries and fuel cells. To increase the reaction rate, the high-efficient electrocatalysts are needed. Among various catalysts, platinum and its alloys are investigated as the best catalyst for the ORR. However, the Pt-based catalysts suffer from many disadvantages, including excessive cost, scarcity, and poor stability. In this work, layered manganese oxides, Li-birnessite, Na-birnessite, K-birnessite and their composites with graphene aerogel were used as the ORR catalysts. The ORR catalytic activity of these materials has been studied using rotating disk electrode (RDE) in O2-saturated and Ar-saturated KOH solution. The linear sweep voltammogram (LSV) curves at scan rate of 10 mVs- 1 show that the Li-birnessite/graphene aerogel provided the best catalytic performance with an onset potential of 0.99 V (V vs. RHE), half wave potential of 0.66 V (V vs. RHE), limiting current density of 5.60 mA cm- 1 (at a rotation rate of 1600 rpm), and Tafel slope of 104.3 mV dec- 1, which is comparable to the Pt catalyst. Moreover, the electron transfer number per oxygen molecule (n) calculated by Koutechy–Levich (K–L) equation is ~ 4, indicating a 4-electron pathway for ORR and suggesting the Li-birnessite manganese oxide coated on graphene aerogel as a high-efficient ORR catalyst.

A Universal Method to Engineer Metal Oxide-Metal-Carbon Interface for Highly Efficient Oxygen Reduction.

Oxygen is the most abundant element in the Earth's crust. The oxygen reduction reaction (ORR) is also the most important reaction in life processes and energy converting/storage systems. Developing techniques toward high-efficiency ORR remains highly desired and a challenge. Here, we report a N-doped carbon (NC) encapsulated CeO2/Co interfacial hollow structure (CeO2-Co-NC) via a generalized strategy for largely increased oxygen species adsorption and improved ORR activities. First, the metallic Co nanoparticles not only provide high conductivity but also serve as electron donors to largely create oxygen vacancies in CeO2. Second, the outer carbon layer can effectively protect cobalt from oxidation and dissociation in alkaline media and as well imparts its higher ORR activity. In the meanwhile, the electronic interactions between CeO2 and Co in the CeO2/Co interface are unveiled theoretically by density functional theory calculations to justify the increased oxygen absorption for ORR activity improvement. The reported CeO2-Co-NC hollow nanospheres not only exhibit decent ORR performance with a high onset potential (922 mV vs RHE), half-wave potential (797 mV vs RHE), and small Tafel slope (60 mV dec-1) comparable to those of the state-of-the-art Pt/C catalysts but also possess long-term stability with a negative shift of only 7 mV of the half-wave potential after 2000 cycles and strong tolerance against methanol. This work represents a solid step toward high-efficient oxygen reduction.

Holey Co, N-codoped graphene aerogel with in-plane pores and multiple active sites for efficient oxygen reduction

Non-noble metal electrocatalysts have emerged as promising next-generation electrocatalysts for oxygen reduction reaction (ORR). Despite considerable progress, non-noble metal electrocatalysts are plagued by relatively low efficiency and poor long-term stability. This study reports the design and synthesis of holey Co, N-codoped graphene aerogel with in-plane pores and multiple active sites (CoN-HGA) for efficient four-electron ORR in both alkaline and acid mediums. In particular, we use etched graphene oxide (GO) sheets with abundant in-plane pores to fabricate the aerogel and a porphyrin containing both Co and N elements as the doping precursor. The as-prepared CoN-HGA, thus, not only inherits abundant defective active sites from the etched GO sheets, but also has plenty of Co- and N-doped active sties. Furthermore, its holey structure creates abundant graphene sheet-sheet contacts as electron pathways, thereby greatly diminishing the resistance of the electrocatalyst. Meanwhile, the in-plane pores also serve as efficient mass transport channels, allowing full access to the internal active sites. Compared with commercial Pt/C (20 wt%), CoN-HGA exhibits slightly higher catalytic activity in alkaline medium and comparable activity in acidic medium with much improved stability and methanol tolerance. The synergetic effect from multiple active sites and unique structure provides a new route to design low-cost, high efficient ORR catalyst and beyond.

Cerium ion intercalated MnO2 nanospheres with high catalytic activity toward oxygen reduction reaction for aluminum-air batteries

Manganese oxide is one of the most extensively studied electrocatalysts for oxygen reduction reaction (ORR) due to its high abundance and environmental friendliness. In this work, cerium ion intercalated birnessite-type manganese oxide (δ-MnO2) dispersed on carbon (CeMnO2/C) with high-efficient oxygen reduction reaction(ORR) electrocatalytic ability in alkaline media is prepared via facile aqueous reactions for the first time. The as-prepared catalyst shows morphology like quasi special nanospheres intertwined by plenty of nanorods just like knitting wool balls. Compared with MnO2/C, the onset and half-wave potential of 4.8% CeMnO2/C shift positively 27 and 57 mV, respectively, and are close to those of Pt/C. The oxygen reduction reaction occurring on 4.8% CeMnO2/C undergoes a 4-electron transfer pathway with the HO2− yield lee than 2%, which is much lower than that produced on Pt/C. The CeMnO2/C catalyst also exhibits excellent long-term stability with current retention of 96.4% after aging for 40000 s. The aluminum-air battery applying 4.8% CeMnO2/C as cathode catalyst gives out the peak power density of 348.8 mW cm−2 in 4 M KOH aqueous solution. After more than 300-h discharging, the voltage degradation of 4.8% CeMnO2/C is only 2% per 100 h. In all, the excellent performance of the Ce-intercalated MnO2/C demonstrates its enormous potential as ORR catalyst in metal-air batteries.