Catalyst Oxygen Research Articles

Reconstructing the Coordination Environment of Fe/Co Dual-atom Sites towards Efficient Oxygen Electrocatalysis for Zn-Air Batteries.

Dual-atom catalysts with nitrogen-coordinated metal sites embedded in carbon can drive the oxygen reduction and evolution reactions (ORR/OER) in rechargeable zinc-air batteries (ZABs), and the further improvement is limited by the linear scaling relationship of intermediate binding energies in the absorbate evolution mechanism (AEM). Triggering the lattice oxygen mechanism (LOM) is promising to overcome this challenge, but has yet been verified since the lacking of bridge oxygen (O) in the rigid coordination environment of the metal centers. Here, we demonstrate that suitably tailored dual-atom catalysts of FeCo-N-C can undergo out-plane and in-plane reconstruction to form the both axial O and bridge O at the metal centers, and thus activate the LOM pathway. The tailored FeCo-N-C with shortened Fe-N bonds also favor the ORR process, therefore is a promising dual-atom oxygen catalyst. The assembled rechargeable ZABs demonstrate a peak power density of 332 mW cm-2, and exhibit no notable decline after ~ 720 h of continuous cycling.

Selective Self‐Assembly of Atomically Dispersed Iron and Cobalt Dual Atom Catalyst on Anisotropic Mesoporous Carbon Particles for High Performance Seawater Batteries

AbstractNa‐seawater batteries (SWBs) are environmentally friendly energy storage system that utilizes abundant seawater as an electrolyte alternative to conventional distilled water‐based and organic electrolytes. To achieve high energy efficiency in Na‐SWBs, it is necessary to enhance the activity of bifunctional oxygen electrocatalysts. In this study, an atomically dispersed iron and cobalt dual‐atom nitrogen‐doped lens‐shaped mesoporous carbon (FeCo‐LMC) particles is synthesized as a SWB cathode material using the spinodal decomposition of the polymer blend and selective precursor positioning. The well‐aligned mesoporous structure and synergetic effect of the dual‐atom site realize FeCo‐LMC as a comparable bifunctional oxygen catalyst with the lowest overpotential difference (EOER−EORR) among the other catalysts with natural seawater electrolyte. When applied to the SWB system, the FeCo‐LMC shows a highly improved charge/discharge performance compared to Pt/C and a stable cycling performance for 200 h. Density functional theory calculations reveal the enhanced oxygen catalytic activity of FeCo‐LMC owing to electron delocalization and d‐band center adjustment of FeN4–CoN4 structure.

N-doped carbon decorated by Cu3P nanoparticle derived from Aspartic acid - Cu MOF as suitable catalysts for oxygen and hydrogen evolution reactions

The preparation of high-efficiency electrocatalysts for the oxygen and hydrogen evolution process (OER and HER) using an easy, green, and facile preparation method is crucial for the effective and economical use of clean energy sources. We report here an eco-friendly phytic acid (PA)-assisted phosphidation strategy to synthesize a novel Cu3P decorated on N-doped carbon (Cu3P-NC). Its synthesis involves precipitation of rode-like microstructured Cu-based aspartic acid frameworks (Asp-Cu MOF), chemical etching of Asp-Cu MOF to form PA cross-linked Cu complexes, and a final pyrolysis step to get Cu3P-NC with abundant Cu3P nanoparticles loaded on N-doped carbon matrix. The Cu3P-NC catalyst demonstrates catalytic performances with low overpotentials of 116 and 310 mV at 10 mA cm−2, small Tafel slopes of 61.2 and 69.2 mV dec−1, for HER and OER respectively, and high catalytic durability in 1 M KOH. The as-prepared Cu3P-NC electrocatalyst offers a new viewpoint on developing multi-functional electrocatalysts in the water-splitting process using environment-friendly substances such as amino acids.

Spatially Immobilized PtPdFeCoNi as an Excellent Bifunctional Oxygen Electrocatalyst for Zinc–Air Battery

AbstractDeveloping efficient oxygen electrocatalysts with low cost, high catalytic activity, and robust stability remains a formidable challenge for rechargeable zinc–air batteries (ZABs). Herein, highly dispersed ultrasmall PtPdFeCoNi high‐entropy alloy nanoparticles with a size of ≈ 2 nm and randomly distributed multimetallic single atoms spatially immobilized on the 3D hierarchically ordered porous nitrogen‐doped carbon skeleton (denoted as PtPdFeCoNi/HOPNC) are successfully synthesized via ultra‐rapid Joule heating process. The spatial immobilization on 3D HOPNC skeleton is the key to the high dispersion of multi‐active sites of oxygen electrocatalysts, and the formed hierarchical pore structure is conducive to the successful construction of the rapid mass transfer channel. As a result, the as‐prepared PtPdFeCoNi/HOPNC exhibits a positive half‐wave potential of 0.866 V versus RHE for oxygen reduction reaction (ORR), a low overpotential of 310 mV at 10 mA cm−2 for oxygen evolution reaction (OER), and low Tafel slopes for both ORR and OER. Furthermore, ZAB using PtPdFeCoNi/HOPNC as bifunctional oxygen catalysts exhibits excellent rate performances and superior cycling stability, surpassing that of a commercial Pt/C‐RuO2 mixture. The spatial immobilization strategy of HOPNC provides a new idea for the design and synthesis of efficient catalysts for various applications.

Unlocking OER potential: Tailoring layered double perovskites through self-reconstruction

The sluggish rate of the anode oxygen evolution reaction (OER) is a major bottleneck for green hydrogen production, making a room-temperature alkaline water electrolyser critical to unlocking the full potential of this technology. Using a perovskite oxide as an electrochemical matrix and forming a self-assembled oxyhydroxide (OOH) layer on the surface via a self-reconstruction activation process (SRAP) is a promising strategy to enhance OER catalytic activity. However, the mechanistic details and long-term impact of SRAP, especially its relationship to catalytic activity, oxygen collection efficiency, and catalyst dissolution, are not fully understood. To address this knowledge gap, we used layered double perovskite (LDP) PrBa0·75Ca0·25Co1·5Fe0·5O5+δ(PBCCF) and PrBa0·75Ca0·25Co1·5Fe0·4Ni0·1O5+δ (PBCCFN) as model electrochemical catalysts and then triggered SRAP. Subsequently, chronoamperometry (CA), rotating ring disk electrode (RRDE) and in-situ electrochemical quartz crystal microbalance (EQCM) were used to study the effect of the Ni-doping on PBCCF SRAP in terms of catalytic activity, oxygen collection efficiency and catalyst stability. The results showed that the OER catalytic current of the LDP PBCCF and PBCCFN was enhanced via SRAP and the oxygen collection efficiency can be maintained, suggesting that the increase in catalytic current is attributed to OER catalytic activity increase rather than electrochemical catalyst dissolution. Additionally, the effect of the catalytic activity enhancement was more significant in PBCCFN. More importantly, the stability of the LDP PBCCF and PBCCFN after SRAP are higher than simple perovskite Ba0·5Sr0·5Co0·8Fe0·2O3-δ (BSCF) because of the increase in the redeposition rate. The observations suggest that using LDP PBCCF and PBCCFN as matrices followed by triggering SRAP can provide valuable insights for designing LDP based OER electrocatalysts.

Co/CoTe heterostructure internal hairy fibers as high-efficiency oxygen electrocatalyst for Zn-air batteries

The design of highly efficient catalysts to enhance the kinetics of oxygen reduction (OER) and oxygen evolution (ORR) reactions is the key issue for the development of high-performance Zn-air battery. In this work, we report the design of Co-CoTe heterostructured fibers as the bifunctional oxygen catalyst for Zn-air battery. Firstly, the theoretical analysis was carried out on Co-CoTe heterostructure. The large work function difference is favorable to construct strong interfacial built-in electric field (BIEF), and the low energy barrier endows high catalytic activities. Moreover, the in-situ grown carbon shell was designed to build “core–shell” Co-CoTe/C unit to realize its high performance. They assemble the Co-CoTe@HFS fiber with good self-supporting and flexible features. Taken the advantages of the strong BIEF, the “core–shell” basic unit, and the freestanding substrate, the Co-CoTe@HFS fiber achieves the good electrocatalytic properties and high reliability. The full Zn-air battery (ZAB) with the Co/CoTe@HFS air cathode achieves the high peak power density and cycling stability over long-term cycling. Therefore, this work provides a clue to design bifunctional oxygen catalysts for high-performance ZABs.

An efficient product design tool for aftertreatment system

A numerical simulation technique based on the conservation of mass and energy in the gas phase has been developed to optimize the aftertreatment system with the lowest costs. Both oxygen storage capacity model and catalyst deterioration model have been integrated into the three-way catalyst performance model. Applications have been discussed, including XY-L 1.5L I3 gasoline turbocharged direct injection (GTDI) production hybrid vehicle, BY-L 1.5L I4 GTDI hybrid vehicle, XY-L (overseas version) 1.5L I4 GTDI hybrid vehicle, and G-L7 1.5L I4 GTDI hybrid vehicle. Vehicle tests in support of the proposed model have been described. The developed model covers the complete range of the cold start, high temperature and volume flow conditions. To optimize a three-way catalyst performance, this work simulated the effect of air fuel ratio, space velocity, temperature, biasing adjustment on the catalyst efficiency. The simulations presented the technique’s capability of well predicting emissions on fresh and full useful life aged aftertreatment systems, respectively, and carried out under transient conditions. The investigation indicated that excess fueling was used upon engine start to heat the catalyst up to its full operating temperature of greater than 350°C. The model results prompted a redesign of the I3 and I4 1.5L GTDI China 6b, Euro VId and Tier 3/SULEV30 exhaust systems over the world light vehicle test procedure (WLTP) and federal test procedure (FTP) cycles, respectively, for example, the model suggested that the latest design for the SULEV30 aftertreatment system on XY-L (overseas version) 1.5L I4 GTDI hybrid vehicle with the revised calibrations in the areas of cold-start and closed-loop fuel treated emissions of NMOG, NOx, and CO to the 70% of the SULEV30 standards with a $64 cost reduction relative to the baseline.

Construction of atom-scale Co/Fe/Ni M-N-C active sites within nitrogen-doped carbon spheres for high-performance bifunctional oxygen catalysts in rechargeable zinc-air batteries

Developing carbon-based catalysts with metal‑nitrogen‑carbon (M-N-C) active sites as efficient and low-cost bifunctional catalysts to replace precious metal catalysts for rechargeable zinc-air batteries devices has garnered significant attention. Herein, nitrogen-doped submicron carbon-based spherical bifunctional electrocatalysts (CNPD-CoFeNi) with abundant atom-scale Co/Fe/Ni M-N-C active sites and defects were synthesized. The introduction of massive amounts of Zn species increases the spatial distance of Co/Fe/Ni metal sites to prevent aggregation during pyrolysis, and the evaporation of Zn at high temperatures creates defects synergizing with M-N-C. Consequently, CNPD-CoFeNi possesses a stable carbon-based spherical structure, high electrical conductivity, rich nitrogen content, abundant atom-scale Co/Fe/Ni M-N-C active sites, and defects, displaying outstanding durability, oxygen reduction reaction (ORR) activity with a half-wave potential of 0.87 V, and satisfactory OER performance, surpassing or comparable with the state-of-art Pt/C and RuO2, respectively. Notably, liquid Zn-air batteries with CNPD-CoFeNi catalyst exhibit an exceptional high peak power density of 146.5 mW cm−2 and stable charge-discharge cycling over 270 h, outperforming Pt/C-RuO2 based devices. Additionally, the all-solid-state Zn-air battery also displays satisfactory practicability and stability. The synthesis strategy and its remarkable results provide valuable guidance and inspiration for the future advancement of precious metal substitutes in ORR/OER and rechargeable zinc-air batteries.

Catalytic depolymerization and hydrodeoxygenation of lignin to high-density fuel precursors using Ni/Nb2O5 catalyst

Converting lignin into renewable fuels via hydrogenolysis is crucial for achieving carbon neutrality. Existing methods primarily produce monomers in the carbon range of 6–9, inadequate for sustainable aviation fuels requiring heavier components. This study introduces a Ni/Nb2O5 catalyst for catalytic transfer hydrogenolysis of organosolv birch lignin with isopropanol, predominantly resulting in dimers and trimers within carbon ranges of 8–16 and 16–30, comprising 24.7 % and 60.5 % of the lignin-oil, respectively. The catalyst's oxygen vacancies and acid sites facilitate efficient C-O and C-C bonds cleavage, preserving a highly aromatic structure with reduced O/C ratio, elevated H/C ratio, and decreased unsaturation. Characterization techniques confirm a significant 55.5 % deoxygenation degree of the lignin-oil, making it suitable for the synthesis of customized fuel across various carbon numbers. This approach offers a practical pathway for obtaining renewable heavier fuel components and precursors from lignin, significantly advancing sustainable fuel technologies.

Regulating active oxygen species and acidity of Ca doped LaMnO3 perovskite catalysts toward efficient n-butylamine oxidation

It is of great significance to design catalysts with high activity, N2 selectivity and stability for nitrogen-containing volatile organic compound (NVOC) catalytic purification. Meanwhile, the role of oxygen species in NVOC catalytic oxidation is still ambiguous. Herein, the oxygen species of La-Mn perovskite catalysts were engineered by doping Ca in La site to elucidate their role in catalytic n-butylamine oxidation. Results demonstrate that La0.9Ca0.1MnO3 exhibits the highest activity owing to its abundant adsorbed oxygen species and high surface area, achieving 100 % n-butylamine conversion (500 ppm; GHSV=60,000 mL g−1h−1) at 200 °C with N2 selectivity of ca. 95 %. More adsorbed oxygen species generated due to Ca doping accelerates the oxidation rate and C-C cleavage of alcohol and acetate intermediates, resulting in higher CO2 yield. Meanwhile, Ca-doping also modifies the acidity of catalysts, which affects the adsorption/desorption process of alkaline substances and yield of nitrogen-containing products. In addition, La0.9Ca0.1MnO3 shows superior stability, high water and SO2 resistance, and acceptable activity for other common NVOCs, demonstrating a promising catalyst for NVOC oxidation even under harsh operation conditions. Furthermore, the toxic effect of pollutant or products during n-butylamine catalytic oxidation on the growth of Chlorella Vulgaris was investigated and results suggest that catalytic oxidation is an environmentally friendly method for NVOC purification. This work sheds light on the relationships among oxygen species, catalyst acidity, and n-butylamine catalytic oxidation, which expand the understanding of rational design of efficient catalyst for NVOC oxidation.

Investigation of membrane-electrode assembly parameters for double-layer anion-exchange membrane-unitized regenerative fuel cell

In this study, we investigate various membrane-electrode assembly (MEA) parameters in the oxygen and hydrogen electrodes for high-efficiency anion-exchange membrane-unitized regenerative fuel cell (AEM_URFC). The effects of catalyst loadings, types of porous transport layer (PTL), and oxygen and hydrogen catalysts were optimized to improve the efficiency of the AEM_URFC. The PTL results indicated that the PTL suitable for fuel cell (FC) exhibited high round-trip efficiency (RTE). Additionally, the types of hydrogen electrode (Pt/C and PtRu/C) were examined. Additionally, AEM_URFCs with different oxygen reduction reaction (ORR) catalyst types (Pt/C and Pt black), and ORR and oxygen evolution reaction catalyst loadings were evaluated. Through our investigations, we developed a high-efficiency AEM_URFC with an RTE of 65.9 % at 20 mA cm−2 (0.871 and 1.572 V (FC and WE modes, respectively)). Moreover, the performance of this AEM_URFC is superior to that of other AEM_URFCs reported in the literature, which is attributed to the reduced ohmic resistance loss caused by the electrical conductivity and hydrophobicity of carbon PTL. Moreover, the AEM_URFC was durable for 5 cycles, indicating that it is cyclable under URFC operation.

Structurally optimized rosette-like microspheres carbon with Fe-Ni single atom sites for bifunctional oxygen electrocatalysis in Zinc-Air batteries

Developing a secure and effective bifunctional oxygen catalyst for the ORR and OER is still a significant obstacle in the design of rechargeable zinc-air batteries. Here, a hollow rose-shaped bifunctional electrocatalyst is synthesized with an sacrificial template strategy (FeNi-NC). X-ray absorption fine structure analysis reveals the FeNi-NC catalyst contains FeN4 and NiN4 active sites as well as FeNi3 alloy. This hollow, flower-like structure performs low density, large specific surface area, and high permeability. Its inner cavities not only provide additional triple-phase interfaces to accelerate the reduction and oxidation of O2, but also enhance the diffusion of reactants on the catalyst. By controlling the input of Fe and nickel metal salts, the dispersion of active sites can be effectively tuned. Owing to the large number of exposed active sites on the carbon nanosheets, the synthesized FeNi-NC catalysts exhibit high electrocatalytic activity in both ORR (E1/2 = 0.852 V) and OER (ηj=10 = 359 mV). The construction of rechargeable zinc-air batteries resulted in a high power density of 135.78 mW cm−2, a better specific capacitance of 726.9 Wh kgZn−1 and 210 h enduring durability. More importantly, density functional theory (DFT) calculations indicate that the electronic interactions between Fe/Ni and nitrogen-doped carbon matrices play a pivotal role in enhancing the electrocatalytic performance of functional groups. These interactions effectively disrupt the electronic neutrality of carbon atoms, thereby accelerating the kinetics of the reaction. This research provides a new method for the preparation of single atom catalysts with bifunctional activities.

Simple generic self-assembly fabrication of transition metal borates on polyaminophenylboric acid modified foam nickel for highly-efficient overall water splitting

Water electrocatalysis for hydrogen production as a prospect strategy to store renewable energy and reduce carbon emissions has attracted great attention, and exploring water electrolysis catalysts has become a research hotspot for widespread industrial water electrolysis application. Very recently, transition metal borates have been demonstrated great potential for electrocatalytic hydrogen or oxygen evolution in alkaline media. However, a generic method for fabricating transition metal borates as bifunctional oxygen catalysts are still challenging. Herein, through a two-step process including poly-aminophenylboronic acid electrodeposition and subsequent electrostatic self-assembly of transitional metal ions, for the first time, to our best knowledge, a simple and generic approach to fabricate polyaminophenylborate transition metal salt modified nickel foam electrodes (PAB-M/NF, M represents transition metal element) was developed for highly efficient water splitting. As a proof of concept, the obtained PAB-Ru/NF exhibited remarkable bifunctional HER and OER catalytic activities and stability in alkaline medium. To drive the HER and OER with a current density of 10 mA cm−2 in 1 M KOH electrolyte, PAB-Ru/NF only required an overpotential of 14 mV and 301 mV, respectively. Moreover, even at a great current density of 250 mA cm−2, PAB-Ru/NF can exhibit very favorable long-term stability for over 35 h. When assembled into an electrolyzer with PAB-Ru/NF as both the anode and cathode, a current density of 10 mA cm−2 can be achieved at a very low cell voltage of 1.50 V. In addition, the other PAB-M/NF catalysts (M including but not limited to Fe, Co and Ni) prepared by the same way also show excellent bifunctional HER and OER catalytic activities and durability. This study provides a prospective and economically feasible generic approach for developing practical bifunctional catalysts for industrial water electrolysis.

Manganese Oxide Gas Diffusion Electrode Conditioning and Electrochemical Doping for Reversible Oxygen Reduction/Evolution Reactions

Developing durable and active bifunctional gas diffusion electrodes for reversible oxygen reduction/evolution (ORR/OER) reaction catalysis is crucial yet challenging in the development of numerous electrochemical energy conversion systems, including regenerative fuel cells and rechargeable metal-air batteries. This research is focused on developing manganese oxide-based gas diffusion electrodes for reversible oxygen electrodes.Core-porous shell Mn/Mn3O4 (abbreviated as MnOx) nanoparticles (QSI) demonstrated increased ORR/OER activities compared to γ-MnO2 (EMD) and b-MnO2.[1] The unique behaviour of core-shell MnOx is attributed to the charge transfer between the low-valent Mn core and the high-valent Mn3O4 shell, thereby regenerating Mn(III) active sites through comproportionation.[1]The stability of transition-metal-based reversible oxygen electrodes remains a challenge. As shown in Figure 1, the deterioration of Mn/Mn3O4 during ORR and OER cycling can be attributed to three aspects: Mn active sites oxidation (Figure 1a), less active MnOx phase formation (Figure 1b), and material loss (carbon corrosion and dissolved MnO4 - formation) (Figure 1c).[2] As a result, the QSI MnOx electrode transformed from pristine to inactive status within 15 galvanostatic ORR/OER cycles. To improve the stability of the electrode, a set of in-situ electrochemical conditioning and electric field-driven metallic cation incorporation into MnOx GDE was investigated. Among the explored metal cations, the Ni2+ incorporation showed the most significant improvement in terms of activity and cyclic stability. The Ni-MnOx GDE demonstrated excellent stability for over 120 galvanostatic cycles at ±10 mA cm-2 in O2-saturated KOH without losing OER activity, surpassing the Pt/C-IrO2 benchmark.[3]These findings position the MnOx electrodes as promising and sustainable alternatives to precious metal-based electrodes for ORR/OER catalysis and provide valuable insights into designing reversible oxygen electrodes for energy conversion and storage in alkaline systems, contributing to a green future.[1] Pei, Y., Wilkinson, D. P., & Gyenge, E. L. Insights into the electrochemical behavior of manganese oxides as catalysts for the oxygen reduction and evolution reactions: monometallic core‐shell Mn/Mn3O4. Small, 2023, 19, 2204585.[2] Pei, Y., Wilkinson, D. P., & Gyenge, E. L. Gas Diffusion Electrode Design and Conditioning with Manganese (III/IV) Oxide Catalyst for Reversible Oxygen Reduction/Evolution Reactions. ACS Energy & Fuels (2023), 37, 23, 19278–19291.[3] Pei, Y., Wu, W. Y., Wilkinson, D. P., & Gyenge, E. L. High-Performance Reversible Oxygen Reduction/Evolution Gas Diffusion Electrodes with Multivalent Cation Doped Core-Shell Mn/Mn3O4 Catalysts. ChemElectroChem, in press. Figure 1

Kinetics of Oxygen Catalyst Based on Pyrochlore Oxide Nano-Particles for Low Temperature Water Electrolysis

Alkaline water electrolysis is carried out at 60 to 80 oC using nickel-based electrode materials and highly concentrated KOH solutions, which make highly corrosive environment against the electrodes, the separator, the current collector, and the others of the cell. Reduction in operating temperature would be preferable to suppress corrosion, although it would also make the catalytic activity for OER and HER down, making the cell voltage up. Since oxygen evolution is known as a high overpotential reaction which is more than 400 mV with nickel-based oxides at 60 oC or more, and alternative materials with lower overpotential and higher stability for OER in AWE have been needed. This paper presents a novel oxygen catalyst nano-particles based on bismuth ruthenium oxide, in which ruthenium at the B site in the pyrochlore structure is partly replaced with manganese1).Mn-doped bismuth ruthenium oxide (MBRO) was prepared by precipitation of metal hydroxide precursor, which had been obtained by addition of NaOH solution into the metal salt solution containing Bi(III) and Ru(III) with Mn(II), followed by calcination at 600 oC. XRD, EDX, EXAFS, ICP-AES, and RBS were used for structural and compositional analyses of MBRO. The obtained oxide was added into distilled water and the solution was treated by ultrasonic vibration to make a suspension, which was then dropped on a titanium disk (4 mm diam.) and dried at RT for 24 h, resulting in oxide particles-coated titanium disk, in which no binders or ionomers were used in the process. The disk was mounted in a commercial rotating disk electrode and was used as the working electrode with a platinum counter electrode, an Hg/HgO reference electrode, and 0.1 mol/L KOH solution. Polarization curves were measured by LSV for OER, of which the results were analyzed to obtain the onset potential, Tafel slope, exchange current density. All measurements were performed at RT (25 oC).EDX and EXAFS studies of MBRO showed that Ru(IV) was replaced with Mn(IV) at the B-site of pyrochlore structure, and this doping made a single phase of pyrochlore structure oxide without sub-product up to 30 at% replacement . Linear sweep voltammetry revealed the overpotential of MBRO for OER was less than 200 mV and the Tafel slope analysis of the LSV curve gave 40 mV/dec or less. The onset potential and the Tafel slope were almost the same when Ru:Mn atomic ratio of MBRO was changed from 100:0 to 70:30 at%. Further analysis of the polarization curve indicated the exchange current density slightly decreased with increasing Mn ratio. These results suggest that Ru is the active site for OER but Mn is as well. The Tafel slope of OER catalysts reported in literatures is mostly 60 mV/dec or more, including more than 200 mV/dec of nickel-based oxides2,3). Therefore, MBRO is a hyper catalytic oxide for OER in alkaline media and can significantly reduce the overpotential of the anode in AWE even at ambient temperature.Ref.1) M. Morimitsu, Patent US.2022085387.A1.2) T. Shinagawa, A. T. Garcia-Esparza, K. Takanabe, Scientific Reports, Vol. 5, Article No.13801 (2015).3) S. Yagi, et al., Nature Communications, Vol. 6, Article No. 8249 (2015).

Design and Preparation at Scale of Ternary NiFe-M-Ox (M=Co, Mo) Catalysts for OER in Alkaline Media

Due to scarcity of Platinum Group Metals (PGMs) widely used in low temperature water electrolysis as cathodes (Hydrogen Evolution Reaction; HER) and anodes (Oxygen Evolution Reaction; OER) a boosting interest to their substitution to Earth abundant elements is observed. It was successfully demonstrated that elements like iron, nickel, cobalt and other (in their oxide and hydroxide forms) can be effective OER catalysts when operate at high pH ranges from 12 to 14 [1-3].This work is devoted to systematic investigation of influence of third element addition to NiFeOx system on a performance and stability of catalysts in alkaline OER. As a co-catalytic elements Mo and Co were selected, based on our previous experience [4,5]. A systematic study on an effect of NiFe-to-M ratio, concentration of precipitation agent and post-treatment temperature were evaluated in a wide range of parameters. Taking into account that mass loading of PGM-free OER catalysts is substantially higher than iridium/ruthenium once and can be up to several milligrams per cm2 all experiments were designed to be scalable. In a laboratory scale reactor, a fascinating batch size of 25g was achieved, using minimal amount of water-based solvents in order to minimize a waste stream generated. Presentation will discuss characterization of obtained materials by SEM, TEM, XPS, XRD and other methods as well as their performance, stability and durability in alkaline conditions, studying Oxygen Evolution Reaction. Acknowledgements and Statements. The authors acknowledge financial support from H2NEW and ElectroCat consortia. References. [1] X. Lyu, J. Li, J. Yang, A. Serov "Significance of Slight Ambient Temperature Variation on the Electrocatalyst Performance toward Oxygen Evolution Reaction" Journal of Environmental Chemical Engineering (2023).[2] X. lyu, A. Serov “Cutting-edge methods for amplifying the oxygen evolution reaction during seawater electrolysis: a brief synopsis” Ind. Chem. Mater., (2023).[3] X. Lyu, Y. Bai, J. Li, R. Tao, J. Yang, A. Serov "Investigation of oxygen evolution reaction with 316 and 304 stainless-steel mesh electrodes in natural seawater electrolysis" J. of Environmental Chemical Engineering 11 (2023) 109667.[4] A. Serov,N. I. Andersen, A. J. Roy, I. Matanovic, K. Artyushkova, P. Atanassov “CuCo2O4 ORR/OER Bi-Functional Catalyst: Influence of Synthetic Approach on Performance”, J. of The Electrochem. Soc. 162 (4) (2015) F449-F454.[5] N. I. Andersen, A. Serov, P. Atanassov “Metal Oxides/CNT Nano-Composite Catalysts for Oxygen Reduction/Oxygen Evolution in Alkaline Media”, Appl. Catal. B: Environmental 163 (2015) 623-627.

(Invited) Catalyst and Anode Design for Durable Alkaline-Membrane Electrolysis

Commercialized membrane electrolyzers use acidic proton exchange membranes (PEMs). These systems offer high performance but require the use of expensive precious-metal catalysts such as IrO2 and Pt that are nominally stable under locally acidic conditions. Alkaline-exchange-membrane (AEM) electrolyzers in principle offer the performance of PEM electrolyzers with the ability to use earth-abundant catalysts and inexpensive bipolar plate materials. I will highlight our fundamental work in understanding the chemical and electrochemical processes in earth-abundant water-oxidation catalysts over the past decade and we are using that understanding to drive progress in high-performance AEM electrolyzers.Baseline systems operate at 1 A·cm-2 in pure water feed at < 1.9 V at a moderate temperature of ~70 °C using either IrO2 or Co3O4 anode catalyst layers, PiperION alkaline ionomers, and stainless-steel porous transport layers. These devices, however, degrade rapidly compared to PEM electrolyzers which we link to chemical and structural changes in the ionomer-catalyst reactive zone using a combination of integrated reference-electrode device architectures, impedance, and cross-sectional and post-mortem materials analysis. We further discover that dynamic Fe-based OER catalysts – that have world-record performance in traditional liquid alkaline electrolyzer systems – perform poorly with enhanced degradation rates in alkaline membrane electrolysis, illustrating fundamentally different chemical design principles for OER catalysts.Given this baseline understanding, I will end with new chemical strategies we have developed to mitigate degradation and enhance performance using novel ionomers, passivated electrolyte-catalyst interfacial architectures, and specifically designed multicomponent anode oxygen catalysts to target stable performance without supporting soluble electrolyte: <10 μV/h degradation at currents > 2 A cm-2 and cell voltages < 2V.

PtCo nanoalloy embedded nitrogen-doped carbon nanotube for rechargeable Zn-air batteries

The large-scale application of metal-air batteries strongly depends on the development of cost-effective, highly efficient, and durable bifunctional oxygen catalysts. In this work, a facile approach for preparing the monodisperse PtCo nanoalloy anchored the nitrogen-doped carbon nanotubes (PtCo/NCNT) for zinc-air batteries is reported. The nitrogen-doped carbon shell prevents PtCo nanoalloy from exfoliation, dissolution, and aggregation and enables the accessibility of electrolytes to the alloy surface and the electron transfer. Besides, the strong interaction between PtCo nanoalloy and nitrogen-doped carbon can efficiently modulate the electronic structure of the formed active sites. When used as a cathode catalyst, the constructed rechargeable zinc-air battery presents higher power density (268 mW cm−2), specific capacity (840 mAh g−1), and excellent stability. More importantly, the PtCo/NCNT catalyst allows the all-solid-state cell to exhibit remarkable flexibility and high round-trip efficiency at various bending states, demonstrating a potential possibility to replace the conventional Pt/C and RuO2 catalysts.

Coaxial MWCNTs/Co-N@N-doped carbon hierarchical porous nanowires as durable air electrode for aqueous Zn-air batteries

Aqueous zinc-air batteries can replace lithium-ion batteries to be used in the future large-scale application. However, efficient bifunctional oxygen catalyst used in air electrode for aqueous zinc-air batteries generally still meet serious challenge. The catalytic activity and stability of air electrode still far from satisfactory. In this work, we designed a series of coaxial MWCNTs/Co-N@N-doped carbon hierarchical porous nanowires (MWCNTs/Co-N@NC) as bifunctional oxygen electrocatalyst with different Co contents. The Co content can facilitate to form the Co-Nx and pyridinic-N to boost the bifunctional oxygen electrocatalysis. The optimal MWCNTs/Co-N@NC-1 delivers superior electrocatalysis for oxygen reduction reaction (ORR) with E1/2 of 0.86 V (vs. RHE) and rational performance for oxygen evolution reaction (OER) with Ej=10 of 1.59 V (vs. RHE) in 0.1 mol/L KOH. In addition, the MWCNTs/Co-N@NC-1-based Zn-air battery exhibits the discharge capacity of 898.84 mAh gZn−1 and a optimal power density of 158.1 mW cm−2 with cycling stability for 300 h. This study provides a strategy to construct robust durability air electrode for aqueous zinc-air batteries.

B-site Doping Boosts the OER and ORR Performance of Double Perovskite Oxide as Air Cathode for Zinc-Air Batteries.

Double perovskite oxides are key players as electrocatalytic oxygen catalysts in alkaline media. In this study, we synthesized B-site doped NdBaCoaFe2-aO5+δ (a= 1.0, 1.4, 1.6, 1.8) electrocatalysts, systematically to probe their bifunctionality and assess their performance in zinc-air batteries as air cathodes. X-ray photoelectron spectroscopy analysis reveals a correlation between iron reduction and increased oxygen vacancy content, influencing electrocatalyst bifunctionality by lowering the work function. The electrocatalyst with highest cobalt content, NdBaCo1.8Fe0.2O5+δ exhibited a bifunctional index of 0.95 V, outperforming other synthesized electrocatalysts. Remarkably, NdBaCo1.8Fe0.2O5+δ, demonstrated facilitated charge transfer rate in oxygen evolution reaction with four-electron oxygen reduction reaction process. As an air cathode in a zinc-air battery, NdBaCo1.8Fe0.2O5+δ demonstrated superior performance characteristics, including maximum capacity of 428.27 mA h at 10 mA cm-2 discharge current density, highest peak power density of 64 mW cm-2, with an outstanding durability and stability. It exhibits lowest voltage gap change between charge and discharge even after 350 hours of cyclic operation with a rate capability of 87.14%.