Shuai Hao

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.

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.

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.

A cobalt-borate nanosheet array: an efficient and durable non-noble-metal electrocatalyst for water oxidation at near neutral pH

Exploitation of efficient water oxidation electrocatalysts under benign conditions is of great importance but remains a huge challenge. In this communication, we report the preparation of a cobalt-borate nanosheet array on a Ti mesh (Co-Bi/Ti) successfully converted from an electrodeposited α-Co(OH)2 nanosheet array in potassium borate (K-Bi) via in situ electrochemical tuning. The Co-Bi/Ti shows high electrocatalytic activity toward water oxidation with an overpotential of 469 mV to achieve a current density of 10 mA cm−2 in 0.1 M K-Bi, with long-term electrochemical stability with a turnover frequency of 0.15 s−1 at an overpotential of 600 mV.

Fe3N-Co2N Nanowires Array: A Non-Noble-Metal Bifunctional Catalyst Electrode for High-Performance Glucose Oxidation and H2O2 Reduction toward Non-Enzymatic Sensing Applications

Among reported electrode materials, a nanoarray is an attractive architecture for molecular detection because of its large specific surface area and easy accessibility for target molecules. Here, a new Fe3 N-Co2 N nanowires array grown on carbon cloth (Fe3 N-Co2 N/CC) is reported as a non-noble-metal bifunctional catalyst electrode for high-performance glucose oxidation and H2 O2 reduction. As an electrochemical non-enzymatic sensor for glucose detection, Fe3 N-Co2 N/CC shows a fast response time of 8 s, a low detection limit (LOD) of 77 nm (signal/noise=3), and a high sensitivity of 4333.7 μA mm-1  cm-2 . As an H2 O2 sensor, it shows a LOD of 59 nm (signal/noise=3) and a sensitivity of 2273.8 μA mm-1  cm-2 with a response time of 2 s. In addition, the proposed sensor is stable with high selectivity, specificity, and reproducibility, and its application for real sample analysis has been successfully demonstrated.

N-Doped carbon dots: a metal-free co-catalyst on hematite nanorod arrays toward efficient photoelectrochemical water oxidation

In this communication, we demonstrate the use of N-doped carbon dots (N-CDs) as a co-catalyst for hematite (α-Fe2O3) nanorod arrays on a Ti sheet for photoelectrochemical water oxidation. Under simulated light irradiation, the photocurrent density of the resulting N-CDs@α-Fe2O3/Ti as a photoanode exhibits a 3.4 times increase with a 280 mV cathode shift of the onset potential relative to that of pristine α-Fe2O3/Ti, with excellent photostability. The up-conversion fluorescent properties of N-CDs enable the absorption of longer wavelength irradiation with emission of short wavelength light to excite α-Fe2O3, leading to the generation of more electron–hole pairs.