Search

Partially hydrous RuO2 nanocluster embedded in a carbon matrix (x-RuO2@C with x = hydration degree = 0.27 or 0.27@C) is presented as a bifunctional catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for water splitting. Symmetric water electrolyzers based on 0.27-RuO2@C for both electrodes showed smaller potential gaps between HER and OER at pH 0, pH 14 and even pH 7 than conventional asymmetric electrolyzers based on two different catalysts (Pt/C || Ir/C) that have been known as the best catalysts for HER and OER respectively. Moreover, 0.27-RuO2@C showed another bifunctional electroactivity for fuel cell electrochemistry involving hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) that are the backward reactions of HER and OER respectively. Pt-level HOR electroactivity was obtained from 0.27-RuO2@C, while its ORR activity was inferior to that of Pt with 200 mV higher overpotential required. The tetra-functionality of 0.27-RuO2@C showed the possibility of realizing single-catalyst regenerative fuel cells.

Synergistic effects of dual homogeneous catalysts for chemical reactions have been reported. Double activation (chemical transformation process where both catalysts work in concert to activate reactants or intermediates) was often responsible for the synergistic effects of dual catalyst systems. Herein, we demonstrate the extension of the double activation from chemo-catalysis to electrocatalysis. The activity of low-cost cobalt oxide electrocatalysts for oxygen reduction reaction (ORR) was significantly improved by introducing secondary-amine-conjugated polymers (HN-CPs) as the secondary promoting electrocatalyst (shortly, promoter). It was proposed that HN-CPs activated neutral diatomic oxygen to partially charged species (O2δ-) in the initial oxygen adsorption step of ORR. Electron donation number of HN-CP to diatomic oxygen (δ in O2δ-) well described the order of activity improvement, i.e., polypyrrole (pPy) > polyaniline (pAni) > polyindole (pInd). The maximum overpotential gain at ~150 mV was achieved by using pPy with the highest δ. Also, it was confirmed that proton of HN-CP was transferred to single oxygen intermediate (*O) of ORR.

An interesting and effective route for improving battery performance using ferroelectric poly(vinylidene difluoride) (PVDF) polymer as a binder material is demonstrated in this work. A ferroelectric PVDF phase developed under the appropriate thermal annealing process enables generation of suitable polarization on active materials during the discharge and charge process, giving rise to longer capacity with lower overpotential at a high current rate. Electrochemical analysis including in situ galvanostatic electrochemical impedance spectroscopy and a galvanostatic intermittent titration measurement revealed that the ferroelectric binder effectively reduced Li-ion diffusion resistance and supported fast migration in the vicinity of active electrodes. Computational results further support that the binding affinity of the ferroelectric PVDF surface is much higher than that of the paraelectric PVDF, confirmed by ideally formed ferroelectric and paraelectric PVDF conformations with Li-ions. Furthermore, we consistently achieved high Li-ion battery (LIB) performance in full cell architecture consisting of a LTO/separator/LFP with a ferroelectric PVDF binder in the anode and cathode materials, revealing that the polarization field is important for fabricating high-performance LIBs, potentially opening a new design concept for binder materials.

It is demonstrated that the electroactivity of the oxygen reduction reaction (ORR) of Pt depends on the structure of a support. Highly conductive two-dimensional titanium carbide (Ti3C2) was selected as the support for Pt because of the expected strong metal-support interaction (SMSI) between Pt and Ti. To control the edge-to-basal ratio, the number of Ti3C2 layers was modulated by exfoliation. Pt nanoparticles (4 nm) were loaded on three different Ti3C2 supports including multi-, few-, and mono-layered Ti3C2 (22L-, 4L-, and 1L-Ti3C2, respectively). The edge-to-basal ratio of layered Ti3C2 increased as the number of layers increased. The edge-dominant support (22L-Ti3C2) donated more electrons to Pt than the basal-dominant supports (4L-Ti3C2 and 1L-Ti3C2). As a result, electron-rich Pt with less d-band vacancies (e.g., Pt/22L-Ti3C2) showed higher ORR activity. In addition, the electron transfer from the support to Pt inducing the strong interaction between Pt and Ti improved the durability of the ORR electroactivity of Pt.

Nanostructured silicon is a promising candidate material for practical use in energy storage devices. However, high temperature operation remains a significant challenge because of severe electrochemical side reactions. Here, we show the design of ultra-durable silicon made by introducing dual coating layers on the silicon surface, allowing stable operation at high temperature. The double layers, which consist of amorphous metal titanate and carbon, provide several advantages including: (i) suppression of volume expansion during Li + insertion; (ii) creation of a stable solid-electrolyte−interface layer; and (iii) preservation of original Si morphology over 600 cycles at high temperature. The resulting silicon-based anode exhibits a reversible capacity of 990 mA h g −1 after 500 cycles at 25 °C and 1300 mA h g −1 after 600 cycles at 60 °C with a rate of 1 C.

A self-charging power cell (SCPC) is a structure that hybridizes the mechanisms for energy conversion and storage into one process through which mechanical energy can be directly converted into electrochemical energy. A key structure of an SCPC is the use of a polyvinylidene fluoride (PVDF) piezo-separator. Herein, we have fabricated a piezoelectric β-form PVDF separator with a highly porous architecture by introducing ZnO particles. The electrochemical charge/discharge performance of this SCPC was greatly enhanced at lower discharge rates compared to highly stretched (high-β-content) or less porous PVDF membranes. The lower charge-transfer resistance of this well-developed porous piezo-separator is the main factor that facilitated the transport of Li+ ions without sacrificing piezoelectric performance. This study reveals a novel approach for improving the performance of SCPCs.

Herein, we report on electrochemical doping of a conducting polymer (CP) with anionically modified graphene nanosheets. The architecture built from reduced graphene oxide (rGO) skeleton skinned by polypyrrole (pPy) enhanced supercapacitor performances especially at high discharge rates superior to those of the same CP with a conventional dopant: e.g., from 141 to 280 F g −1 at 1000C equivalent to ~50 A g −1 . At relatively low rates, the graphene-doped pPy reached the theoretical capacitance of pPy, indicating efficient use of whole electroactive mass.