Zongkui Kou

RuP2-Based Catalysts with Platinum-like Activity and Higher Durability for the Hydrogen Evolution Reaction at All pH Values

Highly active, stable, and cheap Pt-free catalysts for the hydrogen evolution reaction (HER) are under increasing demand for future energy conversion systems. However, developing HER electrocatalysts with Pt-like activity that can function at all pH values still remains as a great challenge. Herein, based on our theoretical predictions, we design and synthesize a novel N,P dual-doped carbon-encapsulated ruthenium diphosphide (RuP2 @NPC) nanoparticle electrocatalyst for HER. Electrochemical tests reveal that, compared with the Pt/C catalyst, RuP2 @NPC not only has Pt-like HER activity with small overpotentials at 10 mA cm-2 (38 mV in 0.5 m H2 SO4 , 57 mV in 1.0 m PBS and 52 mV in 1.0 m KOH), but demonstrates superior stability at all pH values, as well as 100 % Faradaic yields. Therefore, this work adds to the growing family of transition-metal phosphides/heteroatom-doped carbon heterostructures with advanced performance in HER.

Mo2C quantum dot embedded chitosan-derived nitrogen-doped carbon for efficient hydrogen evolution in a broad pH range

A Mo2C quantum dot (averagely 2 nm) embedded N-doped graphitic carbon layer (Mo2C QD/NGCL) is prepared through a simple, green and scalable solid-state reaction. This material exhibits remarkable hydrogen evolution reaction (HER) catalytic activity and durability at all pH values owing to the synergistic effect between Mo2C QDs and NGCLs.

Ultrathin carbon layer stabilized metal catalysts towards oxygen reduction

A novel ultrathin carbon layer (UTCL) stabilized Pt catalyst (Pt-UTCL/C) with an open framework is synthesized to significantly enhance the stability of the catalyst in proton exchange membrane fuel cells. Herein, a cheap and widely available polymer, soluble starch (SS), as a precursor, is employed to wrap Pt nanoparticles (NPs) and is then carbonized into a UTCL with a thickness of few molecular-layers (0.58 nm on average) at a mild temperature. Significantly, it possesses extremely high stabilities of both electrochemical surface area and ORR compared to the commercial Pt/C catalyst even after 10 000 potential cycles. Such excellent stability can be ascribed to the anchoring effect of the UTCL towards Pt NPs to the inhibited migration, agglomeration and detachment of Pt NPs from the supports as well as to the possibly mitigated dissolution-growth process of Pt NPs in light of the UTCL.

Engineered Graphene Materials: Synthesis and Applications for Polymer Electrolyte Membrane Fuel Cells.

Engineered graphene materials (EGMs) with unique structures and properties have been incorporated into various components of polymer electrolyte membrane fuel cells (PEMFCs) such as electrode, membrane, and bipolar plates to achieve enhanced performances in terms of electrical conductivity, mechanical durability, corrosion resistance, and electrochemical surface area. This research news article provides an overview of the recent development in EGMs and EGM-based PEMFCs with a focus on the effects of EGMs on PEMFC performance when they are incorporated into different components of PEMFCs. The challenges of EGMs for practical PEMFC applications in terms of production scale, stability, conductivity, and coupling capability with other materials are also discussed and the corresponding measures and future research trends to overcome such challenges are proposed.

Molybdenum Carbide-Derived Chlorine-Doped Ordered Mesoporous Carbon with Few-Layered Graphene Walls for Energy Storage Applications

In this work, we propose a one-step process to realize the in situ evolution of molybdenum carbide (Mo2C) nanoflakes into ordered mesoporous carbon with few-layered graphene walls (OMG) by chloridization and self-organization, and simultaneously the Cl-doping of OMG (OMG-Cl) by modulating chloridization and annealing processes is fulfilled. Benefiting from the improvement of electroconductivity induced by Cl-doping, together with large specific surface area (1882 cm2 g-1) and homogeneous pore structures, as anode of lithium ion batteries, OMG-Cl shows remarkable charge capacity of 1305 mA h g-1 at current rate of 50 mA g-1 and fast charge-discharge rate within dozens of seconds (a charge time of 46 s), as well as retains a charge capacity of 733 mA h g-1 at a current rate of 0.5 mA g-1 after 100 cycles. Furthermore, as a promising electrode material for supercapacitors, OMG-Cl holds the specific capacitances of 250 F g-1 in 1 M H2SO4 solution and 220 F g-1 at a current density of 0.5 A g-1 in 6 M KOH solution, which are ∼40% and 20% higher than those of undoped OMG electrode, respectively. The high capacitive performance of OMG-Cl material can be due to the additional fast Faradaic reactions induced from Cl-doping species.

Observable Electrochemical Oxidation of Carbon Promoted by Platinum Nanoparticles

The radical degradation of Pt-based catalysts toward oxygen reduction reaction (ORR), predominantly caused by the oxidation of carbon supports, heavily blocks the commercialization of polymer electrolyte membrane fuel cells (PEMFCs). As reported, the electrochemical oxidation of carbon could be accelerated by Pt catalysts; however, hitherto no direct evidence is present for the promotion of Pt catalysts. Herein, a unique ultrathin carbon layer (approximately 2.9 nm in thickness) covered Pt catalyst (Pt/C-GC) is designed and synthesized by a chemical vapor deposition (CVD) method. This magnifies the catalysis effect of Pt to carbon oxidation due to the greatly increased contact sites between the metal-support, making it easy to investigate the carbon oxidation process by observing the thinning of the carbon layer on Pt nanoparticles from TEM observations. Undoubtedly, this finding can better guide the structural design of the durable metal catalysts for PEMFCs and other applications.

Iron-Doped Nickel Phosphide Nanosheet Arrays: An Efficient Bifunctional Electrocatalyst for Water Splitting

Exploring efficient and earth-abundant electrocatalysts for water splitting is crucial for various renewable energy technologies. In this work, iron (Fe)-doped nickel phosphide (Ni2P) nanosheet arrays supported on nickel foam (Ni1.85Fe0.15P NSAs/NF) are fabricated through a facile hydrothermal method, followed by phosphorization. The electrochemical analysis demonstrates that the Ni1.85Fe0.15P NSAs/NF electrode possesses high electrocatalytic activity for water splitting. In 1.0 M KOH, the Ni1.85Fe0.15P NSAs/NF electrode only needs overpotentials of 106 mV at 10 mA cm-2 and 270 mV at 20 mA cm-2 to drive the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Furthermore, the assembled two-electrode (Ni1.85Fe0.15P NSAs/NF∥Ni1.85Fe0.15P NSAs/NF) alkaline water electrolyzer can produce a current density of 10 mA cm-2 at 1.61 V. Remarkably, it can maintain stable electrolysis over 20 h. Thus, this work undoubtedly offers a promising electrocatalyst for water splitting.

Three-Dimensionally Costabilized Metal Catalysts toward an Oxygen Reduction Reaction.

Improving the long-term stability of metal catalysts is crucial to developing polymer electrolyte fuel cells (PEFCs). In this work, we first report an inorganic (TiO2)-organic (perfluorosulfonic acid, PFSA) costabilized Pt catalyst supported on graphene nanosheets (GNS) (Pt-PFSA-TiO2/GNS). Herein, TiO2, as a robust wall, impedes the collision between the metal nanoparticles (NPs) in plane along the horizontal x and y axes, while PFSA mainly anchors the metal NPs to constrain detachment along the vertical z axis. The resulting catalyst displays higher oxygen reduction reaction (ORR) activity in comparison to that of commercial Pt/C. Significantly, the stability is particularly better than that of only PFSA- or TiO2-decorated catalysts (Pt-PFSA/GNS or Pt-TiO2/GNS) and far better than that of Pt/C. After 6000 potential cycles, the half-wave potential (E1/2) of Pt-PFSA-TiO2/GNS decreases by only 16 mV, far less than that of Pt/C (56 mV). The excellent electrochemical property of Pt-PFSA-TiO2/GNS is predominantly attributed to the synergistic effect of PFSA and TiO2 in costabilizing the Pt NP by anchoring and blocking Pt NPs in all three spatial directions. The structural dynamics and mechanism of enhanced properties are also discussed.

Graphene from Amorphous Titanium Carbide by Chlorination under 200°C and Atmospheric Pressures

The synthesis of graphene via decomposition of SiC has opened a promising route for large-scale production of graphene. However, extremely high requirements for almost perfectly ordered crystal SiC and harsh process conditions such as high temperatures (>1200°C) and ultra-high vacuum are two significant challenges hindering its wide use to synthesize graphene by decomposition of SiC. Here, we show that the readily available precursor of carbides, amorphous TiC (a-Ti1-xCx), can be transformed into graphene nanosheets (GNS) with tunable layers by chlorination method at very low temperatures (200°C) and ambient pressures. Moreover, freestanding GNS can be achieved by stripping off GNS from the surface of resulting particles. Therefore, our strategy, the direct transformation of a-Ti1-xCx into graphene, is simple and expected to be easily scaled up.

Core-shell graphene@amorphous carbon composites supported platinum catalysts for oxygen reduction reaction

Abstract A core-shell graphene nanosheets (GNS) and amorphous carbon composite (GNS@a-C) was prepared by a chlorination method and used as a highly efficient catalyst support for oxygen reduction reaction. Herein, GNS as a shell, with excellent conductivity, high surface area, and corrosion resistance, served as a protecting coating to alleviate the degradation of amorphous carbon core. Platinum nanoparticles were homogeneously deposited on the carbon support (Pt/GNS@a-C) and showed a good catalytic activity and a higher electrochemical stability when compared with a commercial Pt/C catalyst. The mass activity of Pt/GNS@a-C catalyst was 0.121 A/mg, which was almost twice as high as that of Pt/C (0.064 A/mg). Moreover, Pt/GNS@a-C retained 51% of its initial electrochemical specific area after 4000 operating cycles when compared with Pt/C (33%). Thus, the prepared catalyst featured excellent electrochemical stability, showing promise for application in polymer electrolyte membrane fuel cells.