Xiaowen Yu

A high-performance three-dimensional Ni–Fe layered double hydroxide/graphene electrode for water oxidation

Water oxidation to evolve oxygen is the key step in water splitting and is related to a variety of energy systems. Here, we report a facile electrodeposition process to immobilize nickel–iron layered double hydroxide (Ni–Fe LDH) nanoplates on three-dimensional electrochemically reduced graphene oxide (3D-ErGO) for water oxidation. This Ni–Fe LDH/3D-ErGO electrode has a three-dimensional interpenetrating network with Ni–Fe nanoplates uniformly decorated on graphene sheets. It has an electrochemically active surface area (EASA) 3.3 times that of conventional planar electrodes. The open porous structure of this electrode also makes its EASA fully accessible to the electrolyte for water oxidation and easy release of oxygen gas. This electrode can be directly used for catalysing the oxygen evolution reaction (OER) in alkaline media without using a binder and conductive additive, exhibiting a small overpotential of 0.259 V and a low Tafel slope of 39 mV dec−1. It outperforms the precious IrO2 catalyst in activity, kinetics, and electrochemical stability.

An ultrahigh-rate electrochemical capacitor based on solution-processed highly conductive PEDOT:PSS films for AC line-filtering

Alternating current (AC) line-filters are widely used to attenuate the leftover AC ripples in line-powered devices. However, the commercialized aluminum electrolytic capacitors (AECs) have low specific capacitances, making them usually the largest components in the electronic circuits of miniaturized, portable and/or flexible electronics. Herein, we report a scalable wet-process to fabricate an electrochemical capacitor (EC) using sulfuric acid treated commercially available poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (AT-PEDOT:PSS) as an electrode material and graphite foil as the current collector. It exhibited high areal (994 μF cm−2) and volumetric (16.6 F cm−3) specific capacitances at 120 Hz, ultrahigh-rate frequency response (phase angle = −83.6° at 120 Hz) with a short resistor–capacitor time constant of 0.15 ms, and an excellent electrochemical stability. Therefore, it is promising to replace AECs for AC line-filtering, and their performance is superior to those of the state-of-the-art ECs for this purpose.

A graphene oxide/oxygen deficient molybdenum oxide nanosheet bilayer as a hole transport layer for efficient polymer solar cells

An annealing-free hole transport layer based on oxygen deficient molybdenum oxide (MoO3−x) nanosheets was developed for polymer solar cells. It showed performance comparable to that of PEDOT:PSS. For better hole extraction, graphene oxide (GO) was introduced to form a GO/MoO3−x bilayer as a hole transport layer to further improve the device performance.

Robust graphene composite films for multifunctional electrochemical capacitors with an ultrawide range of areal mass loading toward high-rate frequency response and ultrahigh specific capacitance

The rapid development of portable electronics requires miniaturized and flexible electrochemical capacitors (ECs) with ultrafast frequency response and/or integrated high capacitive performance. Herein, we report such ECs based on the highly conductive films of reduced graphene oxide (rGO) and commercially available poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) prepared by blade coating or filtration. The typical EC with ultrathin film electrodes exhibited a high-rate frequency response (phase angle = −81.4°) at 120 Hz. On the other hand, ECs with freestanding thick film electrodes exhibited outstanding capacitive performance with a wide range linear relationship between areal capacitance and mass loading. Particularly, an ultrathick film electrode with mass loading up to 33 mg cm−2 delivered ultrahigh areal (5365 mF cm−2) and volumetric (203 F cm−3) specific capacitances at 1 A g−1 (33 mA cm−2). The introduced wet-processing method perfectly integrates thin-film ECs for alternating current (AC) line-filtering and thick-film ECs for compact energy storage in one system, which is promising for practical applications.