Academic literature on the topic 'ORR, Electrochemistry, Pt-free, Zn-air battery'

On account of their high theoretical energy density and minimal cost, Zn-air batteries have gotten a lot of interest as a viable energy storage technology. However, the problem of a high overpotential at the cathode because of the slow oxygen reduction reaction (ORR) kinetics persists. Developing an efficient cathode ORR catalyst and exceeding in performance in comparison to the existing and widely utilized Pt-based catalysts is still a formidable challenge. Herein, this study focuses on the design of a Pt-free catalyst, precisely, Pd/Pd4S based electrocatalysts to enhance ORR performance of cathode. The simple encapsulated structure containing nitrogen-doped carbon (N-doped C) coated Pd/Pd4S and CeO2 nanoparticles (Pd-Pd4S/CeO2/N-C) fabricated by a practical and trouble-free approach has a powerful electrochemical ability. Pd-Pd4S/CeO2/N-C displays a virtually identical limited current density to the commercial 20% Pt/C catalysts and better durability under alkaline conditions. Moreover, this work involves the subsequent utilization of Pd-Pd4S/CeO2/N-C in a primary Zn-air battery as the air electrode, where it manifested comparable current density and power density at 0.6 V as furnished by the Pt/C catalyst. Along with this, the primary Zn-air battery system comprising Pd-Pd4S/CeO2/N-C exhibited constant discharge comprising several hours, a specific capacity of 748 mAh gZn −1, and stability at 10 mA cm−2.

Abstract The high price and unsatisfactory stability of Pt-based catalysts for the sluggish oxygen reduction reaction (ORR) severely limit the development of fuel cells and metal-air batteries. Therefore, developing Pt-free electrocatalysts with excellent activities and stabilities is significant. Herein, an efficient Zn/Fe–N–C electrocatalyst is synthesized via a facile one-pot method. Owing to its curved nanosheet structure, appropriate microporous and mesoporous specific surface areas, abundant defects and high Fe–Nx content, Zn/Fe–N–C exhibits remarkable ORR activity and stability in alkaline electrolyte. Its half-wave potential is 0.843 V, which is 10 mV higher than that of Pt/C. Moreover, Zn/Fe–N–C also manifests satisfactory performance in a practical Zn-air battery. Its maximum output power density is 108.5 mW cm−2, which is equivalent to that of Pt/C. In this work, a simple synthesis method for highly active ORR electrocatalyst is provided, which can be implemented for the future design and synthesis of electrocatalysts used in fuel cells and metal-air batteries.

It is necessary to develop new energy technologies because of serious environmental problems. As one of the most promising electrochemical energy conversion and storage devices, the Zn–air battery has attracted extensive research in recent years due to the advantages of abundant resources, low price, high energy density, and high reduction potential. However, the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) of Zn–air battery during discharge and charge have complicated multi-electron transfer processes with slow reaction kinetics. It is important to develop efficient and stable oxygen electrocatalysts. At present, single-function catalysts such as Pt/C, RuO2, and IrO2 are regarded as the benchmark catalysts for ORR and OER, respectively. However, the large-scale application of Zn–air battery is limited by the few sources of the precious metal catalysts, as well as their high costs, and poor long-term stability. Therefore, designing bifunctional electrocatalysts with excellent activity and stability using resource-rich non-noble metals is the key to improving ORR/OER reaction kinetics and promoting the commercial application of the Zn–air battery. Metal–organic framework (MOF) is a kind of porous crystal material composed of metal ions/clusters connected by organic ligands, which has the characteristics of adjustable porosity, highly ordered pore structure, low crystal density, and large specific surface area. MOFs and their derivatives show remarkable performance in promoting oxygen reaction, and are a promising candidate material for oxygen electrocatalysts. Herein, this review summarizes the latest progress in advanced MOF-derived materials such as oxygen electrocatalysts in a Zn–air battery. Firstly, the composition and working principle of the Zn–air battery are introduced. Then, the related reaction mechanism of ORR/OER is briefly described. After that, the latest developments in ORR/OER electrocatalysts for Zn–air batteries are introduced in detail from two aspects: (i) non-precious metal catalysts (NPMC) derived from MOF materials, including single transition metals and bimetallic catalysts with Co, Fe, Mn, Cu, etc.; (ii) metal-free catalysts derived from MOF materials, including heteroatom-doped MOF materials and MOF/graphene oxide (GO) composite materials. At the end of the paper, we also put forward the challenges and prospects of designing bifunctional oxygen electrocatalysts with high activity and stability derived from MOF materials for Zn–air battery.

Developing superior efficient and durable oxygen reduction reaction (ORR) catalysts is critical for high-performance fuel cells and metal–air batteries. Herein, we successfully prepared a 3D, high-level nitrogen-doped, metal-free (N–pC) electrocatalyst employing urea as a single nitrogen source, NaCl as a fully sealed nanoreactor and gingko shells, a biomass waste, as carbon precursor. Due to the high content of active nitrogen groups, large surface area (1133.8 m2 g−1), and 3D hierarchical porous network structure, the as-prepared N–pC has better ORR electrocatalytic performance than the commercial Pt/C and most metal-free carbon materials in alkaline media. Additionally, when N–pC was used as a catalyst for an air electrode, the Zn–air battery (ZAB) had higher peak power density (223 mW cm−2), larger specific-capacity (755 mAh g−1) and better rate-capability than the commercial Pt/C-based one, displaying a good application prospect in metal-air batteries.

Metal–air batteries and fuel cells have attracted much attention as powerful candidates for a renewable energy conversion system for the last few decades. However, the high cost and low durability of platinum-based catalysts used to enhance sluggish oxygen reduction reaction (ORR) at air electrodes prevents its wide application to industry. In this work, we applied a plasma process to synthesize cobalt nanoparticles catalysts on nitrogen-doped carbon support with controllable quaternary-N and amino-N structure. In the electrochemical test, the quaternary-N and amino-N-doped carbon (Q-A)/Co catalyst with dominant quaternary-N and amino-N showed the best onset potential (0.87 V vs. RHE) and highest limiting current density (−6.39 mA/cm2). Moreover, Q-A/Co was employed as the air catalyst of a primary zinc–air battery with comparable peak power density to a commercial 20 wt.% Pt/C catalyst with the same loading, as well as a stable galvanostatic discharge at −20 mA/cm2 for over 30,000 s. With this result, we proposed the synergetic effect of transitional metal nanoparticles with controllable nitrogen-bonding can improve the catalytic activity of the catalyst, which provides a new strategy to develop a Pt-free ORR electrocatalyst.

Metal-air batteries rely on the oxygen reduction reaction (ORR) for their operation. However, the ORR is kinetically slow, necessitating the use of Pt-based catalysts, which is hindered by their high cost and limited availability. Consequently, considerable efforts have been dedicated to developing metal-free catalysts for the ORR. Among these, heteroatom-doped carbons have emerged as promising candidates by manipulating their composition and microstructure. Inspired by the ancient “Pharaoh’s snakes” reaction, this study utilized sugar, melamine, and a polymerizable ionic liquid as precursors to prepare heteroatom-doped carbons with the desired composition and structure. The resulting carbon catalyst exhibited an onset potential and half-wave potential in a 0.1 M KOH electrolyte that was comparable to those of a commercial Pt/C 20 wt.% catalyst, with values of 0.97 and 0.83 VRHE, respectively. Furthermore, the catalyst demonstrated excellent stability, retaining 93% of its initial current after a 10,800-s test. To evaluate its practical application, the synthesized carbon was employed as the cathode catalyst in a Zn-air battery, which achieved a maximum power density of 90 mW cm−2. This study, therefore, presents a simple yet effective method for producing metal-free heteroatom-doped carbon ORR catalysts used in various energy conversion and storage devices.

Novel synthesis of efficient noble-metal-free electrocatalysts for both oxygen reduction/evolution reaction (ORR/OER) in energy conversion devices (e.g., fuel cells, metal–air batteries) is of essential significance for further sustainable development. This paper reports a facile synthesis of Fe–N–C species-modified carbon nanotubes (F/N-CNTs) for ORR application by directly pyrolyzing a fluffy hybrid precursor at a moderate temperature ([Formula: see text]C) in Ar. The fluffy hybrid precursors consisting of nitro-hydrochloric-acid-treated CNTs, melamine and Fe[Formula: see text] species are prepared via a freeze-drying method. On account of the synergistic effect of various active sites, including pyridine–N, Fe–Nx and Fe3C, and the high conductivity of the CNTs matrix, the as-obtained F/N-CNT electrocatalysts exhibit excellent ORR activities, comparable to commercial Pt/C. The addition of N heteroatoms, the dosage of Fe and the pyrolysis temperature highly influence the ORR properties of the F/N-CNT samples. The typical F/N-CNT sample obtained at the optimized parameters shows an onset potential of 1.06[Formula: see text]V and a half-wave potential of 0.91[Formula: see text]V versus reversible hydrogen electrode (RHE) in an alkaline condition, more positive than those (1.01[Formula: see text]V and 0.88[Formula: see text]V versus RHE) of Pt/C. The F/N-CNT exhibits outstanding bifunctional ORR/OER activity and excellent methanol tolerance, and the F/N-CNT-based Zn–air battery (ZAB) with an open-circuit voltage (OCV) of 1.405[Formula: see text]V presents a current density of 125[Formula: see text]mA[Formula: see text]cm[Formula: see text] and a power density of 76.5[Formula: see text]mW[Formula: see text]cm[Formula: see text]; these electrocatalytic properties are highly superior to Pt/C. The direct pyrolysis of fluffy hybrid precursors provides a concise but robust technical platform to achieve high-performance noble-metal-free electrocatalysts with ORR/OER activities superior to Pt/C.

The oxygen reduction reaction (ORR) has long been of interest in relation to its many energy applications and interesting multi-pathway mechanisms. The ORR is a key reaction in a range of electrochemical energy conversion and storage devices, such as hydrogen fuel cells and metal-air batteries, respectively. These devices are expected to play an ever-increasing role in the global transition to net zero emissions. Metal-air batteries, such as Zn/air batteries, can operate at room temperature, use recyclable materials, are environmentally friendly, and are preferred in relation to consumer safety than batteries relying on organic solvents and reactive electrode species.1 High rates of the ORR are crucial for the development of high performance Zn/air batteries and catalysts play a significant role, with lowering of the catalyst cost also of increasing importance. The costs of conventional Pt-based ORR catalysts are high. Therefore, metal-free carbon-based ORR electrocatalysts are viewed as increasingly promising alternatives, especially as they are lower in cost due to the availability of the precursor materials. Carbon is also a good electrical conductor and support material, is chemically stable, and can have large surface areas. However, the ORR kinetics are sluggish on carbon and chemical and physical modifications are required to enhance its activity. In typical Zn/air batteries, the ORR occurs at the three-phase boundary (TPB) formed between the solid electrode, liquid electrolyte, and gaseous oxygen. The porosity of the catalyst layer, the wettability of the catalyst/electrolyte interface, and the gas permeability and hydrophobicity of the gas diffusion layer (GDL) are thus also important, significantly influencing the cathode performance and durability. The catalyst layer (CL) must therefore be constructed with both a high-performance catalyst and an optimized TPB length to provide high performance without compromising durability. In the current work, we have doped nitrogen into the lattice of a family of nanoporous colloid imprinted carbon (CIC) powders to increase its ORR activity. The CICs are unique for their versatility in terms of pore size control and ease of surface functionalization.2 Pore sizes in the range of 12 to 100 nm were examined and their effect on the ORR activity and mass transport limitations were investigated. To carry out N-doping, the CICs were exposed to ammonia at 800 ˚C for 7 hr. Catalyst inks were then prepared by mixing the CICs with a binder in an isopropyl alcohol/water solution. Aliquots of the ink were drop-casted on the disc of an RRDE system, or were spray coated or drop-casted on a GDL to determine the ORR performance in an in-house Zn/air battery testing cell, with the N-doped CIC catalyst layer sandwiched between an electrolyte chamber and a graphite current collector. In this setup, O2 gas was flowed through the pores in the GDL to the catalyst/electrolyte interface, a Zn wire installed in the electrolyte chamber was used as the reference electrode, and a Ni sponge was used as the counter electrode. The RRDE experiments showed that, after N doping of the CIC powders, the production of peroxide decreased significantly and the ORR onset potential increased to a very respectable value of ca. 0.9 V vs RHE, indicating the successful activation of the ORR. Electron transfer numbers were found to be greater than 3.5, indicating that either a direct or pseudo- 4 electron transfer ORR pathway is dominant. In agreement with the literature, the ORR currents in the kinetic regions increased linearly with mass loading, expected to be proportional to the total active N-doped CIC surface area.3 The N-doped CIC samples retained excellent performance up to a loading of 0.350 μg/cm2 without losing mechanical stability. Similar N-doped CICs and binders of different hydrophobicity were tested in the Zn/air battery testing system. Electrodes made with a hydrophobic NCS microporous layer (MPL) showed much better ORR performance and durability than hydrophilic NCS MPLs. Although electrodes made using hydrophobic polytetrafluoroethylene (PTFE) as the binder in the catalyst layer showed a similar initial performance to those made using hydrophilic Nafion binders, the PTFE based electrodes exhibited better durability. Furthermore, the temperature and pressure used during electrode fabrication were also found to have a significant impact on the binder distribution and ORR performance. Once optimized, a very good correlation was obtained between the N-doped CIC catalyst performance in the RRDE setup and in the Zn/air battery testing system. References J. Pan et al., Adv. Sci., 5, 1700691 (2018). X. Li et al., ACS Appl. Mater. Interfaces, 10, 2130–2142 (2018). N. Gavrilov et al., J. Power Sources, 220, 306–316 (2012).

Developing efficient, durable, and cost-effective non-noble metal catalysts for oxygen reduction reaction (ORR) is necessary to promote the efficiency and performance of Mg-air batteries. Herein, the Co3O4/CuO nanoparticles were synthesized by a low-cost and simple approach using CuCo-based prussian blue analogue (PBA) as precursor of pyrolysis at different calcination temperatures. It was found that the Co3O4/CuO nanoparticles calcined at 600 °C (CCO-600) have relatively small size and superior ORR performance. The onset potential is 0.889 V and the diffusion limiting current density achieves 6.746 mA·cm−2, as well as prominent stability in 0.1 M KOH electrolyte. The electron transfer number of the CCO-600 is 3.89 under alkaline medium, which indicates that the reaction mechanism of ORR is dominated by 4 e process similar to commercial Pt. The primary Mg-air battery with the CCO-600 as the cathode catalyst has been assembled and possesses better discharge performance than the CuCo-based PBA. The open circuit voltage of CCO-600 arrives at 1.76 V and the energy density reaches 1895.95 mWh/g. This work provides an effective strategy to develop non-noble metal ORR catalyst for the application of metal-air batteries.

The unique layered morphology of van der Waals (vdW) heterostructures give rise to a blended set of electrochemical properties from the 2D sheet components. Herein an overview of their potential in energy storage systems in place of precious metals is conducted. The most recent progress on vdW electrocatalysis covering the last three years of research is evaluated, with an emphasis on their catalytic activity towards the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). This analysis is conducted in pair with the most active Pt-based commercial catalyst currently utilized in energy systems that rely on the above-listed electrochemistry (metal–air battery, fuel cells, and water electrolyzers). Based on current progress in HER catalysis that employs vdW materials, several recommendations can be stated. First, stacking of the two types vdW materials, with one being graphene or its doped derivatives, results in significantly improved HER activity. The second important recommendation is to take advantage of an electronic coupling when stacking 2D materials with the metallic surface. This significantly reduces the face-to-face contact resistance and thus improves the electron transfer from the metallic surface to the vdW catalytic plane. A dual advantage can be achieved from combining the vdW heterostructure with metals containing an excess of d electrons (e.g., gold). Despite these recent and promising discoveries, more studies are needed to solve the complexity of the mechanism of HER reaction, in particular with respect to the electron coupling effects (metal/vdW combinations). In addition, more affordable synthetic pathways allowing for a well-controlled confined HER catalysis are emerging areas.