Search

Electrochemical coupling of biomass valorization with carbon dioxide (CO2) conversion provides a promising approach to generate value-added chemicals on both sides of the electrolyzer. Herein, oxygen-vacancy-rich indium oxyhydroxide (InOOH-OV) is developed as a bifunctional catalyst for CO2 reduction to formate and 5-hydroxymethylfurfural electrooxidation to 2,5-furandicarboxylic acid with faradaic efficiencies for both over 90.0% at optimized potentials. Atomic-scale electron microscopy images and density functional theory calculations reveal that the introduction of oxygen vacancy sites causes lattice distortion and charge redistribution. Operando Raman spectra indicate oxygen vacancies could protect the InOOH-OV from being further reduced during CO2 conversion and increase the adsorption competitiveness for 5-hydroxymethylfurfural over hydroxide ions in alkaline electrolytes, making InOOH-OV a main-group p-block metal oxide electrocatalyst with bifunctional activities. Based on the catalytic performance of InOOH-OV, a pH-asymmetric integrated cell is fabricated by combining the CO2 reduction and 5-hydroxymethylfurfural oxidation together in a single electrochemical cell to produce 2,5-furandicarboxylic acid and formate with high yields (both around 90.0%), providing a promising approach to generate valuable commodity chemicals simultaneously on both electrodes. Electrochemical coupling of biomass valorization with CO2 conversion provides a promising approach to generate value-added chemicals on both sides. However, bifunctional catalysts are lacking. Here the authors report oxygen-vacancy-rich indium oxyhydroxide as a bifunctional catalyst for CO2 reduction to formate and 5-hydroxymethylfurfural electrooxidation to 2,5-furandicarboxylic acid with faradaic efficiencies for both > 90.0%. [ABSTRACT FROM AUTHOR]

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

Since the discovery of N-doped carbon nanotubes as the first carbon-based metal-free electrocatalyst (C-MFEC) for oxygen reduction reaction (ORR) in 2009, C-MFECs have shown multifunctional electrocatalytic activities for many reactions beyond ORR, such as oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO2RR), nitrogen reduction reaction (NRR), and hydrogen peroxide production reaction (H2O2PR). Consequently, C-MFECs have attracted a great deal of interest for various applications, including metal–air batteries, water splitting devices, regenerative fuel cells, solar cells, fuel and chemical production, water purification, to mention a few. By altering the electronic configuration and/or modulating their spin angular momentum, both heteroatom(s) doping and structural defects (e.g., atomic vacancy, edge) have been demonstrated to create catalytic active sites in the skeleton of graphitic carbon materials. Although certain C-MFECs have been made to be comparable to or even better than their counterparts based on noble metals, transition metals and/or their hybrids, further research and development are necessary in order to translate C-MFECs for practical applications. In this article, we present a timely and comprehensive, but critical, review on recent advancements in the field of C-MFECs within the past five years or so by discussing various types of electrocatalytic reactions catalyzed by C-MFECs. An emphasis is given to potential applications of C-MFECs for energy conversion and storage. The structure–property relationship for and mechanistic understanding of C-MFECs will also be discussed, along with the current challenges and future perspectives. [ABSTRACT FROM AUTHOR]

Microporous N,P‐codoped graphitic nanosheets (N,P‐CMP‐1000) were synthesized by thermal annealing (1000 °C) of as‐synthesized conjugated microporous polymers (CMPs) in the presence of phytic acid, which can be used as an effective metal‐free electrocatalyst for the oxygen reduction reaction (ORR) for energy conversion. In the whole pH range (i.e. alkaline, acidic, and neutral solutions), the obtained N,P‐CMP‐1000 exhibits superior electrocatalytic activity for ORR with a low overpotential, high current density, and good stability. Furthermore, N,P‐CMP‐1000 can also be applied for electrochemically sensing dissolved oxygen (DO), with a high sensitivity (1.89 μA mg−1 L) and broad detection range (2.56 to 16.65 mg L−1) due to its good electrocatalytic performance towards ORR in neutral solution. In vitro cytotoxicity tests (CCK‐8 and Live/Dead Cell Double Staining Assay) of N,P‐CMP‐1000 extracts demonstrated its good biocompatibility to Human Corneal Epithelial Cells (HCEC), which shows its great potential as an eye‐wearable biosensor for sensing DO in tears. Eye spy: Microporous N,P‐codoped carbon nanosheets were prepared by acid‐catalyzed condensation of commercially available 1,2,4,5‐benzenetetramine and hexaketocyclohexane, followed by carbonization in the presence of phytic acid, which were used as efficient metal‐free electrocatalysts for ORR over whole pH range (i.e. alkaline solution, acidic and neutral solutions), and eye‐wearable biosensors for sensing dissolved oxygen in tears or other body fluids. [ABSTRACT FROM AUTHOR]

Besides their use in fuel cells for energy conversion through the oxygen reduction reaction (ORR), carbon-based metal-free catalysts have also been demonstrated to be promising alternatives to noble-metal/metal oxide catalysts for the oxygen evolution reaction (OER) in metal-air batteries for energy storage and for the splitting of water to produce hydrogen fuels through the hydrogen evolution reaction (HER). This Review focuses on recent progress in the development of carbon-based metal-free catalysts for the OER and HER, along with challenges and perspectives in the emerging field of metal-free electrocatalysis. [ABSTRACT FROM AUTHOR]

In this study, N,P co-doped graphene (NPG) was prepared by a one-step pyrolysis using a mixture of graphene oxide and hexachlorocyclotriphosphazene (HCCP), in which HCCP was used as both the N and P source. Furthermore, it is shown that NPG electrodes, as efficient metal-free electrocatalysts, have a high onset potential, high current density, and long-term stability for the oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

Abstract: The unique hybrid capsules of graphene quantum dots (GQDs) with platinum (Pt)–copper (Cu) nanoparticles have been prepared by a dually spontaneous reduction and assembly process of oxidized graphene quantum dots (ox-GQDs) and Pt precursor by galvanic displacement reaction on Cu microspheres. Cu@PtCu core–shell microspheres were first prepared by reaction of Cu with platinum (IV), which subsequently induced the reduction and assembly of ox-GQDs on them at room temperature. After removal of the Cu cores, the resultant capsules of PtCu@GQDs were collected. Based on the unique hybrid structure, PtCu@GQDs capsules showed remarkably enhanced catalytic activity for oxygen reduction reaction (ORR) with a 2 times higher mass activity and a 40mV more positive onset potential than that of commercial Pt black, indicating the promise of the newly-prepared PtCu@GQDs capsules as catalysts for fuel cell applications. [Copyright &y& Elsevier]

The design and synthesis of cheap, but effective, electrocatalysts for the oxygen reduction reaction in the whole pH range remains a big challenge. Reported herein is a facile method for the synthesis of N,P‐codoped carbon nanosheets by thermal annealing of conjugated microporous polymer in the presence of phytic acid, which were used as efficient metal‐free electrocatalysts for ORR over the whole pH range, and are potential eye‐wearable biosensors for sensing of dissolved oxygen in tears or other body fluids. More information can be found in the Full Paper by H. Chen, J. Qu, L. Dai et al. on page 18487. [ABSTRACT FROM AUTHOR]

Although, metal-free electrocatalysts have been exhibiting attractive oxygen reduction reaction (ORR) performance comparable to Pt/C in alkaline electrolytes, their activity in acidic and neutral mediums is unsatisfactory, hindering their widespread application in energy devices, such as proton exchange membrane fuel cells (PEMFCs), neutral metal-air batteries, and biofuel cells. Herein, N,P,S tri-doped holey carbon (NPS-HC) nanomaterials have been prepared using a one-step method with large specific surface area (1656.0 m2 g−1), abundant holes and edges, and high heteroatom content (7.57 at.%). The optimized NPS-HC exhibits outstanding ORR performance in universal pH mediums, being closely comparable to the commercial Pt/C. The NPS-HC is also utilized as air cathode in alkaline (peak power density: 286.6 mW cm−2 @ 488.1 mA cm−2) and neutral (85.7 mW cm−2 @ 228.8 mA cm−2) electrolytic Zn-air batteries as well as the ORR cathode in a practical PEMFC (275.1 mW cm−2) with comparable or superior performances than the previous reports. Such excellent electrocatalytic performance is attributed to the N,P,S tri-doping induced synergistic charge transfer and spin redistribution along with the hierarchical holey structure with exposed active sites and facilitated mass transport. Thus, this earth-abundant carbon-based nanomaterial holds great potential for high-performance pH-universal ORR catalysis in various energy-related technologies. This article presents a metal-free carbon-based nanomaterial for outstanding ORR performance in universal pH mediums, and its utilization as the air cathode in alkaline and neutral Zn-air batteries as well as the ORR cathode in a practical PEM fuel cell for efficient energy storage and conversion. [Display omitted] • N,P,S tri-doped holey carbon (NPS-HC) is prepared through a one-step method. • NPS-HC has a unique structure with a large specific surface area and abundant holes. • NPS-HC exhibits an outstanding ORR performance in pH-universal mediums. • NPS-HC shows good performance in alkaline/neutral Zn-air batteries and fuel cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • Developing a low-cost and efficient electrocatalyst for CO 2 reduction. • B, N codoping effect and porous structure attributes in catalysis. • Achieving a high FE of 95 % towards CO at low overpotential of 423 mV. • The doped carbon structure with the N or B dopant is key for CO 2 reduction. • Providing the chemical nature of the CO 2 reduction on the catalyst. Efficient and cost-effective electrocatalysts for CO 2 reduction with high selectivity are desirable but remain challenging. Herein, a low-cost and efficient electrocatalyst composed of boron, nitrogen co-doped mesoporous carbon (BNMC) for CO 2 reduction reaction (CO 2 RR) along with the catalytic mechanism are reported. The resultant BNMC (i.e., BNMC-1000) exhibits good CO 2 RR activity with high Faradaic efficiency (FE, 95%) towards CO at low overpotential (423 mV). It is demonstrated that the codoping of nitrogen and boron atom, and the mesopore structure are favorable to the excellent catalytic activity of CO 2 RR. The doped boron atom cooperate with nitrogen atom could adjust the projected density of states of the carbon active site generating a proper adsorbed energy of *COOH and *CO on the carbon surface. This work offers a basic guide for developing metal-free carbon-based CO 2 RR electrocatalysts with high-performance. [ABSTRACT FROM AUTHOR]