Danni Liu

High-Performance Electrolytic Oxygen Evolution in Neutral Media Catalyzed by a Cobalt Phosphate Nanoarray

The topotactic conversion of cobalt phosphide nanoarray on Ti mesh into a cobalt phosphate nanoarray (Co-Pi NA) via oxidative polarization in phosphate-buffered water is presented. As a 3D oxygen evolution reaction (OER) catalyst electrode at neutral pH, the resulting Co-Pi NA/Ti shows exceptionally high catalytic activity and demands an overpotential of only 450 mV to drive a geometrical catalytic current density of 10 mA cm-2 . Notably, this catalyst also shows superior long-term electrochemical stability. The excellent catalytic activity can be attributed to that such 3D nanoarray configuration allows for the exposure of more active sites and the easier diffusion of electrolytes and oxygen.

Energy‐Saving Electrolytic Hydrogen Generation: Ni2P Nanoarray as a High‐Performance Non‐Noble‐Metal Electrocatalyst

It is highly attractive but challenging to develop earth-abundant electrocatalysts for energy-saving electrolytic hydrogen generation. Herein, we report that Ni2 P nanoarrays grown in situ on nickel foam (Ni2 P/NF) behave as a durable high-performance non-noble-metal electrocatalyst for hydrazine oxidation reaction (HzOR) in alkaline media. The replacement of the sluggish anodic oxygen evolution reaction with such the more thermodynamically favorable HzOR enables energy-saving electrochemical hydrogen production with the use of Ni2 P/NF as a bifunctional catalyst for anodic HzOR and cathodic hydrogen evolution reaction. When operated at room temperature, this two-electrode electrolytic system drives 500 mA cm-2 at a cell voltage as low as 1.0 V with strong long-term electrochemical durability and 100 % Faradaic efficiency for hydrogen evolution in 1.0 m KOH aqueous solution with 0.5 m hydrazine.

Three-Dimensional Ni2P Nanoarray: An Efficient Catalyst Electrode for Sensitive and Selective Nonenzymatic Glucose Sensing with High Specificity.

It is highly attractive to construct a natural enzyme-free electrode for sensitive and selective detection of glucose. In this Letter, we report that a Ni2P nanoarray on conductive carbon cloth (Ni2P NA/CC) behaves as an efficient three-dimensional catalyst electrode for glucose electrooxidation under alkaline conditions. Electrochemical measurements demonstrate that the Ni2P NA/CC, when used as a nonenzymatic glucose sensor, offers superior analytical performances with a short response time of 5 s, a wide detection range of 1 μM to 3 mM, a low detection limit of 0.18 μM (S/N = 3), a response sensitivity of 7792 μA mM(-1) cm(-2), and satisfactory selectivity, specificity, and reproducibility. Moreover, it can also be used for glucose detection in human blood serum, promising its application toward determination of glucose in real samples.

A self-standing nanoporous MoP2 nanosheet array: an advanced pH-universal catalytic electrode for the hydrogen evolution reaction

Electrochemical water splitting offers an environmentally friendly route for scalable production of hydrogen fuel but demands low-cost, efficient and robust electrocatalysts for the hydrogen evolution reaction (HER). In this communication, for the first time, we report on the development of a self-standing MoP2 nanosheet array on carbon cloth (MoP2 NS/CC) topotactically converted from its MoS2 NS/CC precursor through a phosphidation reaction. When used as a novel 3D HER cathode in acids, the resulting MoP2 NS/CC shows exceptionally high catalytic activity and strong durability, which only demands an overpotential of 58 mV to drive 10 mA cm−2. Moreover, it also shows high activity and durability in basic and neutral media with the need for overpotentials of only 67 and 85 mV to achieve 10 mA cm−2, respectively. This MoP2 NS/CC catalytic electrode offers us an attractive catalyst material for water-splitting devices for large-scale hydrogen production.

In Situ Derived CoB Nanoarray: A High‐Efficiency and Durable 3D Bifunctional Electrocatalyst for Overall Alkaline Water Splitting

The development of efficient bifunctional catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of extreme importance for future renewable energy systems. This Communication reports the recent finding that room-temperature treatment of CoO nanowire array on Ti mesh by NaBH4 in alkaline media leads to in situ development of CoB nanoparticles on nanowire surface. The resulting self-supported CoB@CoO nanoarray behaves as a 3D bifunctional electrocatalyst with high activity and durability for both HER (<17% current density degradation after 20 h electrolysis) and OER (<14% current density degradation after 20 h electrolysis) with the need of the overpotentials of 102 and 290 mV to drive 50 mA cm-2 in 1.0 m KOH, respectively. Moreover, its two-electrode alkaline water electrolyzer also shows remarkably high durability and only demands a cell voltage of 1.67 V to deliver 50 mA cm-2 water-splitting current with a current density retention of 81% after 20 h electrolysis. This work provides a promising methodology for the designing and fabricating of metal-boride based nanoarray as a high-active water-splitting catalyst electrode for applications.

Ternary NiCoP nanosheet array on a Ti mesh: a high-performance electrochemical sensor for glucose detection

Electrode design is of significant importance in the construction of enhanced electrochemical sensing platforms, and nanoarrays are an attractive architecture in molecule detection with large specific surface area and easy access for target molecules. In this communication, we report on the development of a ternary NiCoP nanosheet array on a Ti mesh (NiCoP/Ti) as a non-noble metal efficient catalyst electrode for electro-oxidation of glucose in alkaline electrolytes. As an electrochemical sensor for glucose detection, NiCoP/Ti shows a fast response time of less than 3 s, a low detection limit of 0.13 μM (S/N = 3), and a high sensitivity of 14 586 μA mM-1 cm-2. This sensor is also stable with high selectivity, specificity and reproducibility, and its application for real sample analysis is also demonstrated successfully.

Copper-Nitride Nanowires Array: An Efficient Dual-Functional Catalyst Electrode for Sensitive and Selective Non-Enzymatic Glucose and Hydrogen Peroxide Sensing

It is highly attractive to develop non-noble-metal nanoarray architecture as a 3D-catalyst electrode for molecular detection due to its large specific surface area and easy accessibility to target molecules. Here, we report the development of a copper-nitride nanowires array on copper foam (Cu3 N NA/CF) as a dual-functional catalyst electrode for efficient glucose oxidation in alkaline solutions and hydrogen peroxide (H2 O2 ) reduction in neutral solutions. Electrochemical tests indicate that such Cu3 N NA/CF possesses superior non-enzymatic sensing ability toward rapid glucose and H2 O2 detection with high selectivity. At 0.40 V, this sensor offers a high sensitivity of 14 180 μA mm cm-2 for glucose detection, with a wide linear range from 1 μm to 2 mm, a low detection limit of 13 nm (S/N=3), and satisfactory stability and reproducibility. Its application in determining glucose in human blood serum is also demonstrated. Amperometric H2 O2 sensing can also been realized with a sensitivity of 7600 μA mm cm-2 , a linear range from 0.1 μm to 10 mm, and a detection limit of 8.9 nm (S/N=3). This 3D-nanoarray architecture holds great promise as an attractive sensing platform toward electrochemical small molecules detection.

High-performance urea electrolysis towards less energy-intensive electrochemical hydrogen production using a bifunctional catalyst electrode

It is highly desirable but still remains a big challenge to develop earth-abundant bifunctional catalysts for urea oxidation and hydrogen evolution electrocatalysis towards more energy-efficient electrolytic hydrogen generation. In this study, we report that nickel phosphide nanoflake arrays on carbon cloth (Ni2P NF/CC) behave as a highly-active durable 3D catalyst electrode for the urea oxidation reaction (UOR) with the required potential of 0.447 V to achieve a geometrical catalytic current density of 100 mA cm−2 in a 1.0 M KOH with 0.5 M urea. Remarkably, the high hydrogen evolution reaction (HER) activity of Ni2P NF/CC enables it to be a bifunctional catalyst for both the UOR and HER towards energy-saving electrochemical hydrogen production, and its two-electrode alkaline electrolyzer requires a cell voltage of only 1.35 V to attain 50 mA cm−2, which is 0.58 V less compared with that required for pure water splitting to achieve the same current density, with remarkable long-term electrochemical durability and nearly 100% Faradaic efficiency for hydrogen evolution.

NiCoP Nanoarray: A Superior Pseudocapacitor Electrode with High Areal Capacitance

High-performance supercapacitors require the design and development of electrode materials with high conductivity and a large electrolyte-accessible surface area. Here, the use of a conductive NiCoP nanoarray on nickel foam (NiCoP/NF) as a superior pseudocapacitor electrode is demonstrated. This 3D electrode exhibits high areal capacitances of 9.2 and 5.97 F cm-2 at current densities of 2 and 50 mA cm-2 , respectively, with good rate capability and cycling stability. The asymmetric supercapacitor (ASC) device assembled using NiCoP/NF as positive electrode and active carbon as negative electrode delivers a high energy density of 1.16 mWh cm-2 at a power density of 1.6 mW cm-2 with 72 % retention of its initial specific capacitance after 2000 cycles at 50 mA cm-2 . The practical use is further demonstrated with two such ASC devices in series to light six LED indicators and also to drive an alkaline water electro- lyzer using NiCoP/NF as both cathode and anode for hydrogen production.

Bimetallic Nickel-Substituted Cobalt-Borate Nanowire Array: An Earth-Abundant Water Oxidation Electrocatalyst with Superior Activity and Durability at Near Neutral pH

There is an urgent demand to develop earth-abundant electrocatalysts for efficient and durable water oxidation under mild conditions. A nickel-substituted cobalt-borate nanowire array is developed on carbon cloth (Ni-Co-Bi/CC) via oxidative polarization of NiCo2 S4 nanoarray in potassium borate (K-Bi). As a bimetallic electrocatalyst for water oxidation, such Ni-Co-Bi/CC is superior in catalytic activity and durability in 0.1 m K-Bi (pH: 9.2), with a turnover frequency of 0.33 mol O2 s-1 at the overpotential of 500 mV and nearly 100% Faradaic efficiency. To drive a geometrical catalytic current density of 10 mA cm-2 , it only needs overpotential of 388 mV, 34 mV less than that for Co-Bi/CC, outperforming reported non-noble-metal catalysts operating under benign conditions. Notably, its activity is maintained over 80 000 s. Density functional theory calculations suggest that the O* to OOH* conversion is the rate-determining step and Ni substitution decreases the free energy on Co-Bi from 2.092 to 1.986 eV.