Interpretation of X-ray Powder Diffraction Patterns . By H. Lipson and H. Steeple. Pp. viii + 335 + 3 plates. (Mac-millan: London; St Martins Press: New York, May 1970.) £4.

X-Ray Diffraction

Porous anodic aluminum oxide: anodization and templated synthesis of functional nanostructures.

To achieve the US Department of Energy 2018 target set for platinum-group metal-free catalysts (PGM-free catalysts) in proton exchange membrane fuel cells, the low density of active sites must be overcome. Here, we report a class of concave Fe–N–C single-atom catalysts possessing an enhanced external surface area and mesoporosity that meets the 2018 PGM-free catalyst activity target, and a current density of 0.047 A cm–2 at 0.88 ViR-free under 1.0 bar H2–O2. This performance stems from the high density of active sites, which is realized through exposing inaccessible Fe–N4 moieties (that is, increasing their utilization) and enhancing the mass transport of the catalyst layer. Further, we establish structure–property correlations that provide a route for designing highly efficient PGM-free catalysts for practical application, achieving a power density of 1.18 W cm−2 under 2.5 bar H2–O2, and an activity of 129 mA cm−2 at 0.8 ViR-free under 1.0 bar H2–air. Iron single-atom catalysts are among the most promising fuel cell cathode materials in acid electrolyte solution. Now, Shui, Xu and co-workers report concave-shaped Fe–N–C nanoparticles with increased availability of active sites and improved mass transport, meeting the US Department of Energy 2018 target for platinum-group metal-free fuel cell catalysts.

Fe–N–C electrocatalyst with dense active sites and efficient mass transport for high-performance proton exchange membrane fuel cells

Two-dimensional materials and single-atom catalysts are two frontier research fields in catalysis. A new category of catalysts with the integration of both aspects has been rapidly developed in recent years, and significant advantages were established to make it an independent research field. In this Review, we will focus on the concept of two-dimensional materials confining single atoms for catalysis. The new electronic states via the integration lead to their mutual benefits in activity, that is, two-dimensional materials with unique geometric and electronic structures can modulate the catalytic performance of the confined single atoms, and in other cases the confined single atoms can in turn affect the intrinsic activity of two-dimensional materials. Three typical two-dimensional materials are mainly involved here, i.e., graphene, g-C3N4, and MoS2, and the confined single atoms include both metal and nonmetal atoms. First, we systematically introduce and discuss the classic synthesis methods, advanced ...

Catalysis with Two-Dimensional Materials Confining Single Atoms: Concept, Design, and Applications.

Proton exchange membrane fuel cells can use hydrogen and air to power clean electric vehicles. However, technical barriers including high cost, limited lifetime and insufficient power density limit their broad applications. Advanced cathode catalysts for the kinetically-sluggish oxygen reduction reaction (ORR) in acidic media are essential for overcoming these barriers. Here, we highlight breakthroughs, challenges and future directions for both platinum group metal (PGM) and PGM-free ORR cathode catalysts. Among PGM catalysts, highly-ordered PtM intermetallic nanostructures exhibit enhanced activity and stability relative to PtM random alloys. Carbon supports, with optimal balance between graphitization degree and porosity, play an important role in enhancing overall performance. Among PGM-free catalysts, transition metal and nitrogen co-doped carbons (M-N-C) perform best. However, degradation at practical voltages (>0.6 V) still prevents their practical application. For all catalysts, translating intrinsic activity and stability into device performance requires electrodes with robust three-phase interfaces for effective charge and mass transfer. Proton exchange membrane fuel cells can efficiently provide clean power for electric vehicles, although more efficient and economic cathode catalysts are still required. This Review highlights recent breakthroughs, challenges and future research directions for Pt group metal (PGM) and PGM-free oxygen reduction catalysts.

Achievements, challenges and perspectives on cathode catalysts in proton exchange membrane fuel cells for transportation

Multifunctional Organic–Inorganic Hybrid Aerogel for Self‐Cleaning, Heat‐Insulating, and Highly Efficient Microwave Absorbing Material

Electromagnetic microwave absorption theory and recent achievements in microwave absorbers

Nonprecious metal catalysts (NPMCs) Fe-N-C are promising alternatives to noble metal Pt as the oxygen reduction reaction (ORR) catalysts for proton-exchange-membrane fuel cells. Herein, a new modulation strategy is reported to the active moiety FeN4 via a precise "single-atom to single-atom" grafting of a Pt atom onto the Fe center through a bridging oxygen molecule, creating a new active moiety of Pt-1-O-2-Fe-1-N-4. The modulated Fe-N-C exhibits remarkably improved ORR stabilities in acidic media. Moreover, it shows unexpectedly high catalytic activities toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), with overpotentials of 310 mV for OER in alkaline solution and 60 mV for HER in acidic media at a current density of 10 mA cm(-2), outperforming the benchmark RuO2 and comparable with Pt/C(20%), respectively. The enhanced multifunctional electrocatalytic properties are associated with the newly constructed active moiety Pt-1-O-2-Fe-1-N-4, which protects Fe sites from harmful species. Density functional theory calculations reveal the synergy in the new active moiety, which promotes the proton adsorption and reduction kinetics. In addition, the grafted Pt-1-O-2- dangling bonds may boost the OER activity. This study paves a new way to improve and extend NPMCs electrocatalytic properties through a precisely single-atom to single-atom grafting strategy.

Single‐Atom to Single‐Atom Grafting of Pt1 onto FeN4 Center: Pt1@FeNC Multifunctional Electrocatalyst with Significantly Enhanced Properties

Hierarchical NiCo2O4/Co3O4/NiO composite was fabricated through a facile hydrothermal method, followed by a post-annealing treatment. The obtained ternary composite, with a flower-like morphology, consists of radially assembled porous nanosheets. Benefiting from the unique structure and the synergistic effect among multiple components, the NiCo2O4/Co3O4/NiO composite exhibited strong electromagnetic wave (EMW) absorption in both low-frequency and high-frequency regions by simply changing its filler loading in the matrix. The absorber with a filler loading of 30 wt% possessed a reflection loss of −28.6 dB at a small layer thickness of 1.64 mm in the Ku band, while the absorber with less filler loading at 20 wt% achieved a reflection loss of −57.0 dB in the C band. The light weight, small thickness, strong and tunable absorbing property of the NiCo2O4/Co3O4/NiO composite make it attractive for developing a high-performance electromagnetic wave absorber.

Ronghai Yu

Papers

Fe–N–C electrocatalyst with dense active sites and efficient mass transport for high-performance proton exchange membrane fuel cells

Multifunctional Organic–Inorganic Hybrid Aerogel for Self‐Cleaning, Heat‐Insulating, and Highly Efficient Microwave Absorbing Material

Electromagnetic microwave absorption theory and recent achievements in microwave absorbers

Single‐Atom to Single‐Atom Grafting of Pt1 onto FeN4 Center: Pt1@FeNC Multifunctional Electrocatalyst with Significantly Enhanced Properties

Hierarchical NiCo2O4/Co3O4/NiO porous composite: a lightweight electromagnetic wave absorber with tunable absorbing performance