Zonghua Pu

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.

General Strategy for the Synthesis of Transition-Metal Phosphide/N-Doped Carbon Frameworks for Hydrogen and Oxygen Evolution

Transition metal phosphides (TMPs) have been identified as promising nonprecious metal electrocatalyst for hydrogen evolution reaction (HER) and other energy conversion reactions. Herein, we reported a general strategy for synthesis of a series of TMPs (Fe2P, FeP, Co2P, CoP, Ni2P, and Ni12P5) nanoparticles (NPs) with different metal phases embedded in a N-doped carbon (NC) matrix using metal salt, ammonium dihydrogen phosphate, and melamine as precursor with varying molar ratios and thermolysis temperatures. The resultant TMPs can serve as highly active and durable bifunctional electrocatalyst toward HER and oxygen evolution reaction (OER). In particular, the Ni2P@NC phase only requires an overpotential of ∼138 mV to derive HER in 0.5 M H2SO4, and ∼320 mV for OER in 1.0 M KOH at the current density of 10 mA cm-2. Because of the encapsulation of NC that can effectively prevent corrosion of embedded TMP NPs, Ni2P@NC exhibits almost unfading catalytic performance even after 10 h under both acidic and alkaline solutions. This synthesis strategy provides a new avenue to exploring TMPs as highly active and stable electrocatalyst for the HER, OER, and other electrochemical applications.

Ultrasmall tungsten phosphide nanoparticles embedded in nitrogen-doped carbon as a highly active and stable hydrogen-evolution electrocatalyst

Rational design and synthesis of highly efficient and stable non-noble metal electrocatalysts are critical for the hydrogen evolution reaction (HER) associated with some renewable energy conversion systems. Herein, we report a one-step facile synthesis of ultrasmall tungsten phosphide nanoparticles (WP NPs) embedded within a nitrogen-doped carbon (NC) matrix (WP NPs@NC). The optimized catalyst, consisting of WP NPs of less than 5 nm diameter encapsulated by ultrathin carbon shells, shows excellent HER activity in strongly acidic media with a low onset overpotential (40 mV), high current density (j = 10 mA cm−2 at η = 102 mV), small Tafel slope (58 mV dec−1), and superior durability (4 days). The as-prepared WP NPs@NC catalyst also offers excellent HER activity in both neutral and alkaline conditions, as well as remarkable durability. This synthesis strategy opens up a new avenue for obtaining transition metal phosphide nanoparticles as a new class of non-noble-metal electrocatalysts for water splitting and hydrogen generation.

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.

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.

Ultrastable nitrogen-doped carbon encapsulating molybdenum phosphide nanoparticles as highly efficient electrocatalyst for hydrogen generation

There is a crucial demand for cost-effective hydrogen evolution reaction (HER) catalysts towards future renewable energy systems, and the development of such catalysts operating under all pH conditions still remains a challenging task. In this work, a one-step facile approach to synthesizing nitrogen-doped carbon encapsulating molybdenum phosphide nanoparticles (MoP NPs@NC) is introduced by using ammonium molybdate, ammonium dihydrogen phosphate and melamine as precursor. Benefitting from structural advantages, including ultrasmall nanoparticles, large exposed surface area and fast charge transfer, MoP NPs@NC exhibits excellent HER catalytic activities with small overpotentials at all pH values (j = 10 mA cm-2 at η = 115, 136 and 80 mV in 0.5 M H2SO4, 1.0 M phosphate buffer solution and 1.0 M KOH, respectively.). Meanwhile, the high catalytic activities of MoP NPs@NC under both neutral and basic conditions have never been achieved before for molybdenum phosphide-based catalysts. Additionally, the encapsulation by N-doped carbon effectively prevents the MoP NPs from corrosion, exhibiting nearly unfading stability after 100 h testing in 0.5 M H2SO4. Thus, our work could pave a new avenue for unprecedented design and fabrication of novel low-cost metal phosphide electrocatalysts encapsulated by N-doped carbon.

Efficient water splitting catalyzed by flexible NiP2 nanosheet array electrodes under both neutral and alkaline solutions

Designing a non-noble-metal catalyst with high efficiency toward oxygen evolution reactions (OERs) is critical for renewable energy storage and conversion devices (e.g., water-splitting and metal–air batteries). In the current study, a flexible electrode of nickel diphosphide nanosheet arrays on carbon cloth (NiP2/CC) is synthesized through phosphidation of Ni(OH)2 nanosheet arrays as a precursor on the carbon cloth. The resultant three-dimensional (3D) porous nanosheet array architecture enhances the exposure of surface active sites and the release of gaseous products. When used as an OER catalyst, such an integrated 3D array electrode affords a current density of 4 mA cm−2 at an OER overpotential of 570 mV with good stability in neutral solution. Moreover, the NiP2/CC electrode also exhibits good OER performance (j = 20 mA cm−2 at η = 310 mV) under alkaline conditions. Notably, this electrode also shows high activity and stability under both neutral and alkaline media toward the HER. More importantly, when assembled as a symmetric full water splitting device with NiP2/CC as both the cathode and anode, a current density of 10 mA cm−2 at a voltage of 1.65 V is achieved in 1.0 M KOH solution. Owing to its low cost and high activity, NiP2/CC presents potential applications toward overall water splitting electrolysis and other electrochemical devices.

Ultrahigh Conductive Copper/Large Flake Size Graphene Heterostructure Thin-Film with Remarkable Electromagnetic Interference Shielding Effectiveness

To guarantee the normal operation of next generation portable electronics and wearable devices, together with avoiding electromagnetic wave pollution, it is urgent to find a material possessing flexibility, ultrahigh conductive, and superb electromagnetic interference shielding effectiveness (EMI SE) simultaneously. In this work, inspired by a building bricks toy with the interlock system, we design and fabricate a copper/large flake size graphene (Cu/LG) composite thin film (≈8.8 μm) in the light of high temperature annealing of a large flake size graphene oxide film followed by magnetron sputtering of copper. The obtained Cu/LG thin-film shows ultrahigh thermal conductivity of over 1932.73 (±63.07) W m-1 K-1 and excellent electrical conductivity of 5.88 (±0.29) × 106 S m-1 . Significantly, it also exhibits a remarkably high EMI SE of over 52 dB at the frequency of 1-18 GHz. The largest EMI SE value of 63.29 dB, accorded at 1 GHz, is enough to obstruct and absorb 99.99995% of incident radiation. To the best of knowledge, this is the highest EMI SE performance reported so far in such thin thickness of graphene-based materials. These outstanding properties make Cu/LG film a promising alternative building block for power electronics, microprocessors, and flexible electronics.

Realizing the Extraction of Carbon from WC to in Situ Formation of W/WC Heterostructures with Efficient Photoelectrochemical Hydrogen Evolution

Although extracting carbon atoms from carbides, as the reverse route to carbide derived carbon (CDC), may have more potentials for constructing advanced nanostructures, it has not been realized yet. As a proof of concept, in this work we realize the extraction of carbon atoms from carbide lattices by rationally controlling the reaction between carbides and Cl2. Thus, a homologous metallic W layer adhered on a WC (W/WC) heterostructure is created. Based on experimental results, such a W/WC heterostructure can be used as an efficient catalyst for the photoelectrocatalytic hydrogen evolution reaction (HER), where the photocurrent density at 0 V can reach up to 16 mA cm-2. Our theoretical calculations disclose that the Mott-Schottky effect accelerates electron flow across the interfaces and significantly decreases the work function of the W facet, which leads to excellent photoelectrocatalytic HER activity on the W facets. The presented results have broad implications since they demonstrate the generic capability to build homologous M/TMC heterostructures.