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A polylaminate coating with intersecting tantalum and tantalum nitride (TaN/Ta/TaN/Ta/TaN/Ta, TaN is the outermost layer) is deposited on surface of 430 stainless steel bipolar plate for high temperature proton exchange membrane fuel cell by a reactive magnetron sputtering method. Electrochemical tests including potentiodynamic, potentiostatic polarisation and electrochemical impedance spectroscopy, are carried out to evaluate the corrosion resistance and stability of the polylaminate TaN/Ta coating in simulating high temperature proton exchange membrane fuel cell environments (85% H 3 PO 4 solution at 80 °C and 130 °C). Results show that the polylaminate TaN/Ta coating greatly improve the corrosion resistance of 430 stainless steel, which can provide almost 100% protection of the substrate in both high temperature proton exchange membrane fuel cell anode and cathode environment. Besides, the interfacial contact resistance of coated 430 stainless steel (9.03 mΩ cm 2 ) is much lower than that of bare substrate (106.74 mΩ cm 2 ). Furthermore, different from the highly increased interfacial contact resistance of bare specimen, the coated 430 stainless steel shows a minor increase resistance after potentiostatic tests in 85% H 3 PO 4 solution at 130 °C.

Titanium/niobium oxides have drawn wide attention due to their attractive high lithium-intercalation voltage avoiding the formation of solid electrochemical interface. However, their poor electronic conductivity hinders the commercial applications because of the low electrochemical kinetics in lithiating and de-lithiating process. In the study, new approach to improving the low conductivity of the conventional oxides in micrometers are tactically proposed via the synergic effect of highly mixed multiphase oxide nanocrystals. Ti-Nb oxide composite microspheres with hierarchical microstructure are fabricated successfully via a very facile method combined solvothermal process and calcination. Interconnected crystalline nanoparticles of TiO 2 , Nb 2 O 5 and TiNb 2 O 7 nanocrystals are involved in the obtained Ti-Nb oxides, demonstrating high structure stability during electrochemical reaction. Meanwhile, the ionic/electronic conductivity is remarkably enhanced by the defects of O 2− vacancies and Ti 3+ /Nb 4+ ions. The remained specific capacity of the multiphase Ti-Nb oxides is up to 185.3 mAh g −1 at 5 C with very weak capacity fade of 5.3% after 1800 cycles, showing a very long cycling stability.

Lithium metal is considered as the ultimate anode candidate for next-generation high-energy storage systems due to its ultrahigh specific capacity and low reduction potential. However, the practical application of lithium metal anode is severely impeded by uncontrollable lithium dendrite growth. In this work, a three-dimensional (3D) N-doped carbon fiber (NCF) network with ion/electron-conductivity has been fabricated by electrospinning the polyacrylonitrile solution and subsequent thermal treatment. The 3D NCF as an interlayer covering on the lithium anode is used to regulate the lithium plating/stripping behavior, accommodating partially deposited Li to realize lithium dendrite-free deposition on the lithium anode. Benefiting from these, the symmetrical cell of Li anode protected by NCF (Li@NCF) delivers long duration time (>1200 h) with a low initial nucleation overpotential (30 mV) at the current density of 1 mA cm−2. In addition, the full cell of Li@NCF||LiFePO4 exhibits excellent capacity retention of 114.6 mAh cm−2 over 360 cycles at the current density of 1 C. This strategy contributes a step forward for dendrite-free lithium metal batteries.

The corrosion behaviour of an AISI 304 stainless steel (304 SS) is investigated in aqueous acid methanol solutions (0.5 M H 2 SO 4 + 2 ppm HF + x M CH 3 OH, x = 0, 1, 5, 10 and 20) at 50 °C to simulate the varied anodic operating conditions of direct methanol fuel cells. Electrochemical measurements including potentiodynamic polarisation, potentiostatic polarisation and electrochemical impedance spectroscopy tests, are employed to analyse the corrosion behaviour. The results reveal that the corrosion resistance of 304 SS is enhanced in solutions with higher methanol content. Scanning electron microscopy and inductively coupled plasma atomic emission spectrometry data indicate that the surface corrosion on 304 SS is alleviated when the methanol concentration is increased. According to the X-ray photoelectron spectroscopy and Mott–Schottky analyses, the passive films formed on the 304 SS after potentiostatic tests in all the test solutions are composed of a duplex electronic structure with an external n-type semiconductor layer and an internal p-type semiconductor layer. Further analyses of the surface conductivity conducted by measuring the interfacial contact resistance between the 304 SS and carbon paper reveal that the passive film formed in the solution with higher methanol content exhibits lower conductivity.

A niobium carbide diffusion layer with a cubic NbC phase surface layer (∼6 μm) and a Nb and C diffusion subsurface layer (∼1 μm) is fabricated on the surface of AISI 304 stainless steel (304 SS) bipolar plate in a proton exchange membrane fuel cell (PEMFC) using plasma surface diffusion alloying. The electrochemical behaviour of the niobium carbide diffusion-modified 304 SS (Nb–C 304 SS) is investigated in simulated PEMFC environments (0.5 M H 2 SO 4 and 2 ppm HF solution at 80 °C). Potentiodynamic, potentiostatic polarisation and electrochemical impedance spectroscopy measurements reveal that the niobium carbide diffusion layer considerably improves the corrosion resistance of 304 SS compared with untreated samples. The corrosion current density of Nb–C 304 SS is maintained at 0.058 μA cm −2 and 0.051 μA cm −2 under simulated anodic and cathodic conditions, respectively. The interfacial contact resistance of Nb–C 304 SS is 8.47 mΩ cm 2 at a compaction force of 140 N cm −2 , which is significantly lower than that of the untreated sample (100.98 mΩ cm 2 ). Moreover, only a minor increase in the ICR of Nb–C 304 SS occurs after 10 h potentiostatic tests in both cathodic and anodic environments.

AISI 304 stainless steel (SS) has been niobized by a plasma surface diffusion alloying method. A 3 μm niobized layer with dominant niobium elements has been formed on the 304 SS surface and the performances of the niobized 304 SS has been examined and evaluated as bipolar plate for proton exchange membrane fuel cell (PEMFC). Results show that the average contact angle with water for the niobized 304 SS is about 90.4°, demonstrating better hydrophobicity as compared with the untreated 304 SS (68.1°). The corrosion resistance of the 304 SS is considerably improved by the niobized layer with the corrosion current densities decreased at 0.2 and 0.4 μA cm −2 in simulated PEMFC anode purged with hydrogen and the cathode purged with air condition (0.05 M H 2 SO 4 + 2 ppm F − solution at 70 °C), respectively. The interfacial contact resistance (ICR) for the as-prepared niobized 304 SS is 10.53 mΩ cm 2 at the compaction of 140 N cm −2 . Furthermore, after 4 h potentiostatic tests, the niobizied specimens exhibit much lower ICR than that for the untreated ones. Thus, the niobized layer can act as a conductively protective layer of the 304 SS bipolar plate for PEMFC.

A niobium nitride diffusion coating has been prepared by plasma surface diffusion alloying method on the surface of AISI 304 stainless steel (304 SS) which is applied to bipolar plates for proton exchange membrane fuel cell (PEMFC). The as-prepared niobium nitride diffusion coating consists of a niobium nitride surface layer (8–9 μm) and a Nb and N diffusion solid solution subsurface layer (1–2 μm). The corrosion resistance of the niobium nitride modified 304 SS are investigated and evaluated in simulated PEFMC operating conditions (0.05 M H 2 SO 4 + 2 ppm F − solution at 70 °C). Results show that the niobium nitride diffusion coating greatly improves the corrosion resistance of 304 SS. Self-corrosion potentials of niobium nitride modified 304 SS increase considerably up to 100 mV and 143 mV (vs. SCE) while corrosion current densities remain low at 0.127 μA cm −2 and 0.071 μA cm −2 in simulated anodic and cathodic environment, respectively. Interfacial contact resistance (ICR) of niobium nitride modified 304 SS is 9.26 mΩ cm 2 under 140 N cm −2 compaction force, which is much lower than that of untreated 304 SS, 100.98 mΩ cm 2 . After 4 h potentiostatic polarization test, the niobium nitride modified 304 SS exhibits sufficiently low ICR values 2 .

Electrochemical behavior of a high Cr and Ni austenitic stainless steel (HCN) is investigated and 316L SS in a simulated proton exchange membrane fuel cell environments is also investigated, and interfacial contact resistance (ICR) is measured before and after potentiostatic polarization. Both stainless steels underwent passivation in both anode and cathode environments for proton exchange membrane fuel cell. Passive current density of HCN is lower than that of 316L SS. An increase in ICR between carbon paper and HCN results from passive film formed during the potentiostatic polarization.

A dense and supersaturated nitrogen layer with higher conductivity is obtained on the surface of austenitic stainless steel 304L by the low temperature plasma nitriding. The effect of plasma nitriding on the corrosion behavior and interfacial contact resistance (ICR) for the austenitic stainless steel 304L was investigated in 0.05 M H 2 SO 4 + 2 ppm F − simulating proton exchange membrane fuel cell (PEMFC) environment using electrochemical and electric resistance measurements. The experiment results show that the stable passive film is formed after the potentiostatic polarization at the specified anodic or cathodic potentials under PEMFC operation condition, and the plasma nitriding improves slightly the corrosion resistance and decreases markedly the ICR of 304L. The ICR of the plasma nitrided 304L increases after the potentiostatic polarizations for 4 h, and lower than 100 mΩ cm 2 at the compaction force of 150 N cm −2 .

High ionic conductivity, varying from 0.01 to 1 S cm −1 between 300 and 700 °C, has been achieved for the hybrid and nano-ceria-composite electrolyte materials, demonstrating a successful application for advanced low temperature solid oxide fuel cells (LTSOFCs). The LTSOFCs were constructed based on these new materials. The performance of 0.15–0.25 W cm −2 was obtained in temperature region of 320–400 °C for the ceria-carbonate composite electrolyte, and of 0.35–0.66 W cm −2 in temperature region of 500–600 °C for the ceria-lanthanum oxide composites. The cell could even function at as low as 200 °C. The cell has also undergone a life test for several months. A two-cell stack was studied, showing expected performance successfully. The excellent LTSOFC performance is resulted from both functional electrolyte and electrode materials. The electrolytes are two phase composite materials based on the oxygen ion and proton conducting phases, or two rare-earth oxides. The electrodes used were based on the same composite material system having excellent compatibility with the electrolyte. They are highly catalytic and conductive thus creating the excellent performances at low temperatures. These innovative LT materials and LTSOFC technologies would open the door for wide applications, not only for stationary but also for mobile power sources.