Isolated Single Iron Atoms Anchored on N-Doped Porous Carbon as an Efficient Electrocatalyst for the Oxygen Reduction Reaction

A Durable Nickel Single-Atom Catalyst for Hydrogenation Reactions and Cellulose Valorization under Harsh Conditions

Hydrothermally stable, acid-resistant nickel catalysts are highly desired in hydrogenation reactions, but such a catalyst remains absent owing to the inherent vulnerability of nickel under acidic conditions. An ultra-durable Ni-N-C single-atom catalyst (SAC) has now been developed that possesses a remarkable Ni content (7.5 wt %) required for practical usage. This SAC shows not only high activities for hydrogenation of various unsaturated substrates but also unprecedented durability for the one-pot conversion of cellulose under very harsh conditions (245 °C, 60 bar H₂ , presence of tungstic acid in hot water). Using integrated spectroscopy characterization and computational modeling, the active site structure is identified as (Ni-N4)⋅⋅⋅N, where significantly distorted octahedral coordination and pyridinic N constitute a frustrated Lewis pair for the heterolytic dissociation of dihydrogen, and the robust covalent chemical bonding between Ni and N atoms accounts for its ultrastability.

Monodisperse Ultrasmall Manganese-Doped Multimetallic Oxysulfide Nanoparticles as Highly Efficient Oxygen Reduction Electrocatalyst

The highly efficient and cheap non-Pt-based electrocatalysts such as transition-based catalysts prepared via facile methods for oxygen reduction reaction (ORR) are desirable for large-scale practical industry applications in energy conversion and storage systems. Herein, we report a straightforward top-down synthesis of monodisperse ultrasmall manganese-doped multimetallic (ZnGe) oxysulfide nanoparticles (NPs) as an efficient ORR electrocatalyst by simple ultrasonic treatment of the Mn-doped Zn-Ge-S chalcogenidometalate crystal precursors in H₂O/EtOH for only 1 h at room temperature. Thus obtained ultrasmall monodisperse Mn-doped oxysulfide NPs with ultralow Mn loading level (3.92 wt %) not only exhibit comparable onset and half-wave potential (0.92 and 0.86 V vs reversible hydrogen electrode, respectively) to the commercial 20 wt % Pt/C but also exceptionally high metal mass activity (189 mA/mg at 0.8 V) and good methanol tolerance. A combination of transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical analysis demonstrated that the homogenous distribution of a large amount of Mn(III) on the surface of NPs mainly accounts for the high ORR activity. We believe that this simple synthesis of Mn-doped multimetallic (ZnGe) oxysulfide NPs derived from chalcogenidometalates will open a new route to explore the utilization of discrete-cluster-based chalcogenidometalates as novel non-Pt electrocatalysts for energy applications and provide a facile way to realize the effective reduction of the amount of catalyst while keeping desired catalytic performances.

Zirconium-Porphyrin-Based Metal-Organic Framework Hollow Nanotubes for Immobilization of Noble-Metal Single Atoms

Single atoms immobilized on metal-organic frameworks (MOFs) with unique nanostructures have drawn tremendous attention in the application of catalysis but remain a great challenge. Various single noble-metal atoms have now been successfully anchored on the well-defined anchoring sites of the zirconium porphyrin MOF hollow nanotubes, which are probed by aberration-corrected scanning transmission electron microscopy and synchrotron-radiation-based X-ray absorption fine-structure spectroscopy. Owing to the hollow structure and excellent photoelectrochemical performance, the HNTM-Ir/Pt exhibits outstanding catalytic activity in the visible-light photocatalytic H₂ evolution via water splitting. The single atom immobilized on MOFs with hollow structures are expected to pave the way to expand the potential applications of MOFs.

DUT-58 (Co) Derived Synthesis of Co Clusters as Efficient Oxygen Reduction Electrocatalyst for Zinc-Air Battery

To meet the requirement of fuel cells and metal-air batteries, non-noble metal catalysts have to be developed to replace precious platinum-based catalysts. Herein, Co nanoclusters (≈2 nm) are anchored on nitrogen-doped reduced graphene oxide (Co/N-r-GO) by using DUT-58 (Co) metal-organic framework and GO as precursors. Compared with single-atom catalysts usually with ultralow concentration (<0.5 wt%), Co nanoclusters are more beneficial to break the O-O bond to ensure four electronic way for oxygen reduction reaction (ORR), since they can provide more adsorption centers for reactants. Therefore, as expected, the sample with 6.67 wt% Co content (Co/N-r-GO-5%-850) exhibits better ORR activity with a higher half-wave potential of 0.831 V, a more positive onset potential of 0.921 V than Pt/C, and a comparable limiting current density in alkaline medium. The Co nanoclusters enhance the catalytic performance for ORR in three aspects: quantum size effects, metal-support interactions, and low-coordination environment of metal centers. Furthermore, the sample is assembled into a zinc-air battery as the outstanding durable ORR catalyst. It displays a higher specific capacity (795 mAh g-1 at the current density 50 mA cm-2) and power density (175 mW cm-2) than Pt/C (731 mAh g-1 and 164 mW cm-2, respectively).

Porous graphene doped with Fe/N/S and incorporating Fe3O4 nanoparticles for efficient oxygen reduction

The honeycomb-like structured graphene was used to synthesize a 3D porous graphene doped with Fe/N/S and incorporating Fe₃O₄ nanoparticles. It showed comparable ORR activity to Pt/C, in alkaline media.

Potential-Cycling Synthesis of Single Platinum Atoms for Efficient Hydrogen Evolution in Neutral Media

Single-atom catalysts (SACs) have exhibited high activities for the hydrogen evolution reaction (HER) electrocatalysis in acidic or alkaline media, when they are used with binders on cathodes. However, to date, no SACs have been reported for the HER electrocatalysis in neutral media. We demonstrate a potential-cycling method to synthesize a catalyst comprising single Pt atoms on CoP-based nanotube arrays supported by a Ni foam, termed PtSA-NT-NF. This binder-free catalyst is centimeter-scale and scalable. It is directly used as HER cathodes, whose performances at low and high current densities in phosphate buffer solutions (pH 7.2) are comparable to and better than, respectively, those of commercial Pt/C. The Pt mass activity of PtSA-NT-NF is 4 times of that of Pt/C, and its electrocatalytic stability is also better than that of Pt/C. This work provides a large-scale production strategy for binder-free Pt SAC electrodes for efficient HER in neutral media.

Ionically dispersed Fe(ii)–N and Zn(ii)–N in porous carbon for acidic oxygen reduction reactions

A bimetallic Fe, Zn/N/C catalyst with high metal loading, demonstrating high activity for ORR processes in acidic electrolytes.