Coordination-tailored d-Orbital Occupancy: A Catalytic Descriptor for Single-atom Electrocatalysts in Oxygen Reduction Reaction

Anion-Modulated Platinum for High-Performance Multifunctional Electrocatalysis toward HER, HOR, and ORR.

Today, the development of active and stable catalysts still represents a challenge to be overcome in the research field of low-temperature fuel cells.[...]

Surface modification of MnCo2O4 with conducting polypyrrole as a highly active bifunctional electrocatalyst for oxygen reduction and oxygen evolution reaction

A novel 2D Co3(HADQ)2 metal-organic framework as a highly active and stable electrocatalyst for acidic oxygen reduction

Atomically precise electrocatalysts for oxygen reduction reaction

Three-dimensional nanocomposites derived from combined metal organic frameworks doped with Ce, La, and Cu as a bifunctional electrocatalyst for supercapacitors and oxygen reduction reaction

Nanoporous carbons derived from metal-conjugated phosphoprotein/silica: Efficient electrocatalysts for oxygen reduction and hydrazine oxidation reactions

To replace precious platinum (Pt)-based electrocatalysts for cathodic oxygen reduction reaction (ORR), edge-selectively sulfurized graphene nanoplatelets (SGnP) are synthesized as efficient metal-free electrocatalysts simply by ball-milling pristine graphite in the presence of sulfur (S8 ). The resultant SGnPs exhibit remarkable electrocatalytic activity toward ORR with better tolerance to methanol crossover/CO poisoning effects and longer-term stability than those of pristine graphite and commercial Pt/C electrocatalysts. Edge-Selectively Sulfurized Graphene Nanoplatelets as Efficient Metal-Free Electrocatalysts for Oxygen Reduction Reaction: The Electron Spin Effect.

High demand of energy, environmental problems, and energy crisis have brought great attentions in renewable and environment-friendly energy resources(1). Among various candidate energy sources, electrochemistry based energy storage and harvesting devices such as rechargeable batteries, supercapacitors, utilized regenerative fuel cells(URFCs), and solar cells have received great interests (1, 2). Particularly, URFCs which include fuel cells and water electrolyzers are getting a big spotlight in the renewable energy fields due to their high efficiency and clean properties(3, 4). The key technology for URFCs is to develop the cost-effective, durable, and high catalytic active catalysts for oxygen reduction(ORR) and evolution reactions(OER) in order to decrease the overpotential and improve efficiency of cells (5). Ideal bifunctional ORR and OER catalysts are Pt, RuO, and IrO for URFCs(6-8). However, precious metal-based catalysts are inadequate in terms of price competitiveness and limited durability to commercialize the URFCs(9). Recently, modification of cobalt oxides nanostructures with various dopants have reported to reduce the overpotential with high OER and ORR performances (10). Furthermore, nitrogen-doped graphene oxide is used to further enhance the electronic conductivity with durable mechanical property, because nitrogen sites can function as electrochemical active sites(11). In this work, several short-length N-doped carbon nanofibers(N-CNF) are introduced to maximize electrochemical active sites of catalysts. The shortened N-CNF catalysts are synthesized by the hydrothermal method. The physicochemical properties of the N-CNF-supported cobalt oxides nanostructures are investigated by various tools such as X-ray diffraction, scanning electron microscope, Brunauer Emmett Teller, and transmission electron microscope. To analyze electrochemical activities, rotating ring disk electrode system is used with an Hg/HgO, a platinum wire, and a 0.1M KOH solution for reference, counter, and electrolyte respectively. The electrochemical characteristics are measured by linear sweep voltammetry at a scan rate of 5 mVs-1 for OER (1.2V–1.7V) and ORR (0.2V–1.2V). To analyze the long-term stability for OER and ORR, the accelerated degradation tests are performed at a scan rate of 200 mVs-1. References Wang H-F, Tang C, Zhang Q. Template growth of nitrogen-doped mesoporous graphene on metal oxides and its use as a metal-free bifunctional electrocatalyst for oxygen reduction and evolution reactions. Catalysis Today. 2017. Kushwaha HS, Halder A, Thomas P, Vaish R. CaCu3Ti4O12: A Bifunctional Perovskite Electrocatalyst for Oxygen Evolution and Reduction Reaction in Alkaline Medium. Electrochimica Acta. 2017;252(Supplement C):532-40. Bau VM, Bo XJ, Guo LP. Nitrogen-doped cobalt nanoparticles/nitrogen-doped plate-like ordered mesoporous carbons composites as noble-metal free electrocatalysts for oxygen reduction reaction. J Energy Chem. 2017;26(1):63-71. Zhang X, Ding P, Sun Y, Li X, Li H, Guo J. CoMoS3.13 nanosheets grafted on B, N co-doped graphene nanotubes as bifunctional catalyst for efficient water electrolysis. Journal of Alloys and Compounds. 2018;731(Supplement C):403-10. Yang J, Fujigaya T, Nakashima N. Decorating unoxidized-carbon nanotubes with homogeneous Ni-Co spinel nanocrystals show superior performance for oxygen evolution/reduction reactions. Scientific Reports. 2017;7. Song W, Ren Z, Chen SY, Meng Y, Biswas S, Nandi P, et al. Ni- and Mn-Promoted Mesoporous Co3O4: A Stable Bifunctional Catalyst with Surface-Structure-Dependent Activity for Oxygen Reduction Reaction and Oxygen Evolution Reaction. ACS Applied Materials and Interfaces. 2016;8(32):20802-13. Elumeeva K, Masa J, Tietz F, Yang F, Xia W, Muhler M, et al. A Simple Approach towards High-Performance Perovskite-Based Bifunctional Oxygen Electrocatalysts. ChemElectroChem. 2016;3(1):138-43. Lee DU, Park MG, Park HW, Seo MH, Ismayilov V, Ahmed R, et al. Highly active Co-doped LaMnO3 perovskite oxide and N-doped carbon nanotube hybrid bi-functional catalyst for rechargeable zinc-air batteries. Electrochem Commun. 2015;60:38-41. Zhao BT, Zhang L, Zhen DX, Yoo S, Ding Y, Chen DC, et al. A tailored double perovskite nanofiber catalyst enables ultrafast oxygen evolution. Nat Commun. 2017;8. So IS, Kim NI, Cho SH, Kim YR, Yoo J, Seo Y, et al. Enhancement of Bifunctional Activity of the Hybrid Catalyst of Hollow-Net Structure Co3O4 and Carbon Nanotubes. J Electrochem Soc. 2016;163(11):F3041-F50. Kim NI, Afzal RA, Choi SR, Lee SW, Ahn D, Bhattacharjee S, et al. Highly active and durable nitrogen doped-reduced graphene oxide/double perovskite bifunctional hybrid catalysts. Journal of Materials Chemistry A. 2017;5(25):13019-31.

Methanol crossover severely limits the performance ofdirect methanolfuel cells (DMFCs) by introducing methanol to the cathode compartment,where it competes with the oxygen reduction reaction (ORR) and poisonsplatinum-based ORR electrocatalysts, making it essential to developmethanol-tolerant ORR electrocatalysts. Here, Ni doping is exploredas a means of improving the electrocatalytic activity and methanoltolerance of LaCo1–xNixO3 (x = 0, 0.1, 0.15,and 0.2) perovskite oxide electrocatalysts synthesized using a simplesol–gel method. X-ray diffraction (XRD), Fourier transforminfrared (FTIR), X-ray photoelectron spectroscopy (XPS), and energy-dispersiveX-ray (EDAX) analysis confirm the formation of LaCoO3 andsuccessful Ni doping at the Co site. Field-emission scanning electronmicroscopy (FE-SEM) analysis reveals that the particle size of thesynthesized nanoparticles slightly increases upon Ni doping. Althougha corresponding decrease in Brunauer–Emmett–Teller (BET)surface area with increasing Ni doping is also found, LaCo0.8Ni0.2O3 possesses the highest pore volume andpore radius among all the synthesized perovskite oxides. This optimizedcomposition exhibits superior ORR catalytic activity (0.724 and 0.678V vs reversible hydrogen electrode (RHE) at current densities of −0.1and −0.3 mA cm–2, respectively) comparableto Pt/C (0.758 and 0.709 V vs RHE) derived from the linear sweep voltammetry(LSV) study performed at 1600 rpm. In the presence of methanol, allthe synthesized perovskite oxides experienced a small negative potentialshift (0 to 14 mV) during ORR, suggesting these materials can be usedas methanol-tolerant ORR electrocatalysts in DMFCs.

A mini review on carbon-based metal-free electrocatalysts for oxygen reduction reaction

It is an immense challenge to develop bifunctional electrocatalysts for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) in low temperature fuel cells and rechargeable metal-air batteries. Herein, a simple and cost-effective approach is developed to prepare novel materials based on carbon nanotubes (CNTs) and a hexagonal boron nitride (h-BN) nanocomposite (CNT/BN) through a one-step hydrothermal method. The structural analysis and morphology study confirms the formation of a homogeneous composite and merging of few exfoliated graphene layers of CNTs on the graphitic planes of h-BN, respectively. Moreover, the electrochemical study implies that CNT/BN nanocomposite shows a significantly higher ORR activity with a single step 4-electron transfer pathway and an improved onset potential of +0.86 V versus RHE and a current density of 5.78 mA cm-2 in alkaline conditions. Interestingly, it exhibits appreciably better catalytic activity towards OER at low overpotential (η=0.38 V) under similar conditions. Moreover, this bifunctional catalyst shows substantially higher stability than a commercial Pt/C catalyst even after 5000 cycles. Additionally, this composite catalyst does not show any methanol oxidation reactions that nullify the issues due to fuel cross-over effects in direct methanol fuel cell applications.

Spinel CoFe2O4 /carbon nanotube composites as efficient bifunctional electrocatalysts for oxygen reduction and oxygen evolution reaction

Facile preparation of biomass-derived bifunctional electrocatalysts for oxygen reduction and evolution reactions

An enhanced non-noble perovskite-based oxygen electrocatalyst for efficient oxygen reduction and evolution reactions