Yipu Liu

Coupling Mo2C with Nitrogen-Rich Nanocarbon Leads to Efficient Hydrogen-Evolution Electrocatalytic Sites

In our efforts to obtain electrocatalysts with improved activity for water splitting, meticulous design and synthesis of the active sites of the electrocatalysts and deciphering how exactly they catalyze the reaction are vitally necessary. Herein, we report a one-step facile synthesis of a novel precious-metal-free hydrogen-evolution nanoelectrocatalyst, dubbed Mo2 C@NC that is composed of ultrasmall molybdenum carbide (Mo2 C) nanoparticles embedded within nitrogen-rich carbon (NC) nanolayers. The Mo2 C@NC hybrid nanoelectrocatalyst shows remarkable catalytic activity, has great durability, and gives about 100 % Faradaic yield toward the hydrogen-evolution reaction (HER) over a wide pH range (pH 0-14). Theoretical calculations show that the Mo2 C and N dopants in the material synergistically co-activate adjacent C atoms on the carbon nanolayers, creating superactive nonmetallic catalytic sites for HER that are more active than those in the constituents.

Carbon-Armored Co9S8 Nanoparticles as All-pH Efficient and Durable H2-Evolving Electrocatalysts

Splitting water to produce hydrogen requires the development of non-noble-metal catalysts that are able to make this reaction feasible and energy efficient. Herein, we show that cobalt pentlandite (Co9S8) nanoparticles can serve as an electrochemically active, noble-metal-free material toward hydrogen evolution reaction, and they work stably in neutral solution (pH 7) but not in acidic (pH 0) and basic (pH 14) media. We, therefore, further present a carbon-armoring strategy to increase the durability and activity of Co9S8 over a wider pH range. In particular, carbon-armored Co9S8 nanoparticles (Co9S8@C) are prepared by direct thermal treatment of a mixture of cobalt nitrate and trithiocyanuric acid at 700 °C in N2 atmosphere. Trithiocyanuric acid functions as both sulfur and carbon sources in the reaction system. The resulting Co9S8@C material operates well with high activity over a broad pH range, from pH 0 to 14, and gives nearly 100% Faradaic yield during hydrogen evolution reaction under acidic (pH 0), neutral (pH 7), and basic (pH 14) media. To the best of our knowledge, this is the first time that a transition-metal chalcogenide material is shown to have all-pH efficient and durable electrocatalytic activity. Identifying Co9S8 as the catalytically active phase and developing carbon-armoring as the improvement strategy are anticipated to give a fresh impetus to rational design of high-performance noble-metal-free water splitting catalysts.

Coupling Sub‐Nanometric Copper Clusters with Quasi‐Amorphous Cobalt Sulfide Yields Efficient and Robust Electrocatalysts for Water Splitting Reaction

Superefficient water-splitting materials comprising sub-nanometric copper clusters and quasi-amorphous cobalt sulfide supported on copper foam are reported. While working together at both the anode and cathode sides of an alkaline electrolyzer, this material gives a catalytic output of overall water splitting comparable with the Pt/C-IrO2 -coupled electrolyzer.

Metallic Co9S8 nanosheets grown on carbon cloth as efficient binder-free electrocatalysts for the hydrogen evolution reaction in neutral media

The development of efficient non-noble metal hydrogen-evolving electrocatalysts is of paramount importance for sustainable hydrogen production from water. Herein, we report the direct growth of metallic Co9S8 nanosheets on carbon cloth (CC) through a facile one-pot solvothermal method. We also show that the introduction of a tiny amount of Zn2+ ions (Zn : Co mol ratio of 0.5–1 : 100) in the synthesis system can reduce the thickness, improve the crystallinity, and optimize the surface structure of Co9S8 nanosheets, without Zn-doping. Furthermore, we show that the resulting Co9S8/CC materials can serve as efficient, binder-free, non-noble metal electrocatalysts for the hydrogen evolution reaction (HER) under neutral conditions (pH 7). In particular, the Co9S8/CC material (synthesized in the presence of Zn2+ ions) affords a current density of 10 mA cm−2 at a low overpotential of 175 mV, has great catalytic stability as long as 100 h, and gives about 100% faradaic yield towards the HER in neutral media. The materials excellent catalytic performance toward the HER is attributed primarily to the synergistic effects of Co9S8s intrinsic catalytic ability, the ultrathin nanosheet array architecture and the self-supporting feature.

Ultrafast Formation of Amorphous Bimetallic Hydroxide Films on 3D Conductive Sulfide Nanoarrays for Large‐Current‐Density Oxygen Evolution Electrocatalysis

Developing nonprecious oxygen evolution electrocatalysts that can work well at large current densities is of primary importance in a viable water-splitting technology. Herein, a facile ultrafast (5 s) synthetic approach is reported that produces a novel, efficient, non-noble metal oxygen-evolution nano-electrocatalyst that is composed of amorphous Ni-Fe bimetallic hydroxide film-coated, nickel foam (NF)-supported, Ni3 S2 nanosheet arrays. The composite nanomaterial (denoted as Ni-Fe-OH@Ni3 S2 /NF) shows highly efficient electrocatalytic activity toward oxygen evolution reaction (OER) at large current densities, even in the order of 1000 mA cm-2 . Ni-Fe-OH@Ni3 S2 /NF also gives an excellent catalytic stability toward OER both in 1 m KOH solution and in 30 wt% KOH solution. Further experimental results indicate that the effective integration of high catalytic reactivity, high structural stability, and high electronic conductivity into a single material system makes Ni-Fe-OH@Ni3 S2 /NF a remarkable catalytic ability for OER at large current densities.

Highly Active, Nonprecious Electrocatalyst Comprising Borophene Subunits for the Hydrogen Evolution Reaction

Developing nonprecious hydrogen evolution electrocatalysts that can work well at large current densities (e.g., at 1000 mA/cm2: a value that is relevant for practical, large-scale applications) is of great importance for realizing a viable water-splitting technology. Herein we present a combined theoretical and experimental study that leads to the identification of α-phase molybdenum diboride (α-MoB2) comprising borophene subunits as a noble metal-free, superefficient electrocatalyst for the hydrogen evolution reaction (HER). Our theoretical finding indicates, unlike the surfaces of Pt- and MoS2-based catalysts, those of α-MoB2 can maintain high catalytic activity for HER even at very high hydrogen coverage and attain a high density of efficient catalytic active sites. Experiments confirm α-MoB2 can deliver large current densities in the order of 1000 mA/cm2, and also has excellent catalytic stability during HER. The theoretical and experimental results show α-MoB2s catalytic activity, especially at large current densities, is due to its high conductivity, large density of efficient catalytic active sites and good mass transport property.

Growth of molybdenum carbide micro-islands on carbon cloth toward binder-free cathodes for efficient hydrogen evolution reaction

Design and synthesis of efficient noble metal-free hydrogen evolution catalysts is of paramount importance for the practical application of water-splitting devices. Herein, we report a novel synthetic method to grow dispersed molybdenum carbide (Mo2C) micro-islands on flexible carbon cloth (CC). This method involves the controlled synthesis of a supramolecular hybrid between cetyltrimethyl ammonium cations and molybdate anions on CC, followed by simple thermal treatment of this supramolecular hybrid in Ar to form Mo2C on CC in situ. In this synthesis, the presence of cetyltrimethyl ammonium bromide is proven to be important because it effectively immobilizes molybdate ions on CC on the one hand and functions as a carbon source for the formation of Mo2C on the other. Moreover, the as-prepared Mo2C/CC composite material can serve as efficient binder-free cathodes toward the hydrogen evolution reaction (HER). The Mo2C/CC affords a current density of 10 mA cm−2 at a low overpotential of 140 mV and works stably in acidic media with a Faraday yield of ∼100%. The isolated island architecture of Mo2C ensures rich active sites to be exposed and allows the easy interaction of reactants (e.g., protons) with the active sites. Also, the strong adhesion between Mo2C and carbon cloth facilitates electron transport/transfer in the composite material and is helpful for the achievement of excellent catalytic stability.

From solid-state metal alkoxides to nanostructured oxides: a precursor-directed synthetic route to functional inorganic nanomaterials

Functional nanostructured oxides are important inorganic materials for various energy- and environment-related applications, such as photocatalysis and lithium ion batteries. To optimize their properties/functions, synthetic methods that can lead to nanomaterials with unique composition, morphology and size are highly desirable. In this review, we summarize recent research efforts towards the construction of nanostructured solid-state metal alkoxides-a family of inorganic–organic hybrid compounds and their conversion into functional inorganic nanomaterials. The chemical transformation from metal alkoxides to nanostructured oxides represents a novel precursor-directed synthetic route to functional inorganic nanomaterials. The uniqueness of this method mainly lies in: (i) the crystal/molecular structure of metal alkoxides which plays a crucial role in their nanosized structures; (ii) the use of metal alkoxides as precursor materials which determines the composition and (micro)structure of the finally-obtained oxide nanomaterials; and (iii) that this method can be employed to synthesize nanomaterials that cannot be readily achieved using other approaches.

Well-dispersed CoS2 nano-octahedra grown on a carbon fibre network as efficient electrocatalysts for hydrogen evolution reaction

Increasing the number of active sites of a non-noble metal catalyst is an effective route to make its overall catalytic performance close to that of noble metals. Herein, we report a novel confinement strategy for preparing well-dispersed octahedral CoS2 nanocrystals through in situ sulfidization of the carbon fibre-wrapped Co nanoparticles, in order to fully expose the active sites of every nanocatalytic unit. The successful synthesis of the material includes three main steps: (i) electrospinning synthesis of Co ion-containing polyacrylonitrile fibres (Co2+-PANF), (ii) thermal conversion of the Co2+-PANF at 900 °C under N2 atmosphere into a Co-embedded carbon fibre network (Co-CFN), and (iii) direct sulfidization of Co-CFN using sublimed sulphur, leading to the confinement growth of CoS2 nano-octahedra on CFN. Furthermore, this material, denoted as CoS2-CFN, can serve as a highly active, stable, non-noble metal electrocatalyst for hydrogen evolution reaction in acidic medium. This material generates a current density of 10 mA cm−2 at a small overpotential of 136 mV with about 100% Faradaic yield and maintains its catalytic activity for at least 20 hours. The excellent catalytic properties of CoS2-CFN are attributed primarily to the synergistic effects of the intrinsic catalytic ability of CoS2, the well-dispersed CoS2 nanocrystals as the catalytically active phase, as well as the high conductivity and porous structure of the carbon fibre network as a support material.

Facile precursor-mediated synthesis of porous core–shell-type Co3O4 octahedra with large surface area for photochemical water oxidation

A porous Co3O4 material with unique octahedron-in-octahedron core–shell-type morphology is prepared via a facile precursor-mediated synthetic route. This material possesses large surface area and good catalytic activity for water oxidation reaction.