Low Interfacial Contact Resistance Research Articles

Electrochemical properties of niobium and niobium compounds modified AISI430 stainless steel as bipolar plates for DFAFC

ABSTRACTThe highly conductive and corrosion resistant diffusion layers of niobium, niobium nitrides and niobium carbides have been successfully fabricated on AISI430 stainless steel (430 SS) via a plasma surface diffusion alloying (PSDA) method as bipolar plates for direct formic acid fuel cells (DFAFCs). The surface of niobium carbides modified 430 SS (NbC 430 SS) is relative densification and uniformity without other surface flaw and micropore. Potentiodynamic and potentiostatic polarisation measurements indicate that NbC 430 SS enhances the corrosion resistance more effectively than other modified samples and its corrosion current density is maintained approximately 2.5 μA cm–2 in the simulated anodic environment of DFAFC. Moreover, NbC 430 SS presents a superior hydrophobicity with a contact angle of 105.5° and a lower interfacial contact resistance (ICR) before and after potentiostatic polarisation tests than other specimens. Therefore, NbC 430 SS developed in this work has a great potential to be bipolar plates for DFAFCs.

Coated stainless steel as bipolar plate material for anion exchange membrane fuel cells (AEMFCs)

Low-temperature anion-exchange membrane fuel cells (AEMFCs) are gathering increased attention because they facilitate the use of non-precious metal catalysts, which might drastically reduce costs compared to low-temperature proton exchange membrane fuel cells (PEMFCs). Metallic, e.g., stainless steel, bipolar plates (BPPs) present a cost-efficient solution for this type of cell. However, anodic film formation at high positive potentials (approx. +1.5 V vs. RHE) on uncoated metals/stainless steels leads to high interfacial contact resistance (ICR) of the BPP once exposed to such a potential. A potential of +1.5 V vs. RHE is commonly reached under local and global hydrogen starvation, which rules out the use of uncoated metals in AEMFCs. We have investigated the ICR change and oxide film formation of several materials under simulated fuel cell operating conditions and found that suppression of anodic film formation and, in turn, low ICRs can be achieved by carbon coating of stainless steels.

Low temperature processed efficient and stable perovskite solar cell

MA0.6FA0.4PbI3 material based efficient and stable perovskite solar cells (PSCs) are fabricated by electron transport layer (ETL) interfacial modification. The highest power conversion efficiency (PCE) of device was ~ 17%. Cesium acetate and cesium carbonate were used with low temperature processed sol-gel ZnO ETL for interface modifications. Low leakage current and enhanced dark injection current are observed from dark current-voltage measurement. From the electrochemical impedance spectroscopy (EIS) measurement higher recombination resistance and lower interfacial contact resistance are observed in the PSC devices. Mott-Schottky analysis also shows the higher flat-band potential and enhanced device performance with cesium acetate ETL. Cesium acetate related ZnO ETL has large grain size which leads to reduce the device series resistance and contact resistance in PSC compared to cesium carbonate ETL related device. Perovskite film on cesium acetate ETL has better surface morphology, topography and hydrophobicity characterization compared to perovskite film grown on cesium carbonate ETL film. The material work function and electron injection barrier are also investigated by X-Ray photoelectron spectroscopy (XPS) measurement and ultraviolet photoelectron spectroscopy (UPS). From electrochemical impedance spectroscopy measurements the charge transport behaviour and trap-assisted carrier recombination are estimated. Fabricated PSCs device stability has been measured for a month-long degradation study. The PSC device stability is observed four times higher with cesium acetate PSCs compared to cesium carbonate ETL related PSCs. The overall device PCE is around 82% higher with cesium acetate compared to cesium carbonate devices.

Molybdenum carbide coated 316L stainless steel for bipolar plates of proton exchange membrane fuel cells

Superior corrosion resistance and high electrical conductivity are crucial to the metallic bipolar plates towards a wider application in proton exchange membrane fuel cells. In this work, molybdenum carbide coatings are deposited in different thicknesses onto the surface of 316 L stainless steel by magnetron sputtering, and their feasibility as bipolar plates is investigated. The microstructure characterization confirms a homogenous, compact and defectless surface for the coatings. The anti-corrosion performance improves with the increase of the coating thickness by careful analysis of the potentiodynamic and potentiostatic data. With the adoption of a thin chromium transition layer and coating of a ∼1052 nm thick molybdenum carbide, an excellent corrosion current density of 0.23 μA cm−2 is achieved, being approximately 3 orders of magnitude lower than that of the bare stainless steel. The coated samples also show a low interfacial contact resistance down to 6.5 mΩ cm2 in contrast to 60 mΩ cm2 for the uncoated ones. Additionally, the hydrophobic property of the coatings’ surface is beneficial for the removal of liquid water during fuel cell operation. The results suggest that the molybdenum carbide coated stainless steel is a promising candidate for the bipolar plates.

Effect of temperature and bias voltage on electrical and electrochemical properties of diamond-like carbon films deposited with HiPIMS

The relatively high electrical resistivity of diamond-like carbon (DLC) film is one of the main drawbacks when applied in electronic device. In this study, DLC films were synthesized on 304 stainless steels by high power impulse magnetron sputtering (HiPIMS) process and the effect of deposition temperature and bias voltage on the microstructure, electrical and electrochemical properties, hardness and adhesion strength of the DLC films were investigated. The sp2/sp3 ratio of DLC films first decreased then increased and the surface became denser as bias voltage increasing from 0 to −400 V. While the film turned into graphite-like structure and became incompact when deposition temperature rose from 100 °C to 300 °C. The interfacial contact resistance (ICR) got reduced by increasing bias voltage and deposition temperature. However, as the deposition temperature increased to 300 °C the anticorrosion ability and hardness of DLC films deteriorated. The DLC films deposited at 300 °C presented soft and had better adhesion strength than hard DLC films deposited at 100 °C. DLC films deposited at −400 V bias and 300 °C had the lowest ICR while DLC films deposited at −400 V bias and 100 °C had the best performance when ICR, corrosion resistance and hardness were all taken into consideration.

Evaluation of Ni-Cr-P coatings electrodeposited on low carbon steel bipolar plates for polymer electrolyte membrane fuel cell

Polymer electrolyte membrane fuel cell (PEMFC) stacks suffer from the high cost and low volumetric energy of non-porous graphite bipolar plates. To resolve this problem, a bilayer coating consisting of Ni and Ni–Cr–P is deposited on AISI 1020 low-carbon steel using pulse electrodeposition. Ni/Ni–Cr–P-coated AISI 1020 is evaluated as a bipolar plate material for PEMFCs. Ni/Ni–Cr–P-coated substrates exhibit better corrosion resistance in both cathodic (air-purging) and anodic (H2-purging) environment than the bare AISI 1020 substrate and lower interfacial contact resistance (ICR) than bare AISI 1020 and stainless steel. Further, it is expected to show better water management as the Ni/Ni–Cr–P coating is more hydrophobic than the bare substrate. Preliminary studies show that Ni/Ni–Cr–P-coated AISI 1020 plate can be a suitable candidate for replacing graphite as the bipolar plate of PEMFCs.

Potential of ITO thin film for electrical probe memory applications

ABSTRACTElectrical probe memory has received considerable attention during the last decade due to its prospective potential for the future mass storage device. However, the electrical probe device with conventional diamond-like carbon capping and bottom layers encounters with large interfacial contact resistance and difficulty to match the experimentally measured properties, while its analog with titanium nitride capping and bottom layers also faces serious heat dissipation through either probe and silicon substrate. Therefore, the feasibility of using indium tin oxide (ITO) media for the capping and bottom layers of the electrical probe device is investigated by tailoring the thickness and electrothermal properties of the ITO capping and bottom layers within experimentally established range and subsequently calculating the resultant temperature at several predefined points based on a previously developed three-dimensional model. To meet the required temperature and to fit the experimentally reported values, the thickness, electrical conductivity, and thermal conductivity of the ITO capping and bottom layers are found to be 5 nm, 103 Ω−1 m−1, 0.84 W m−1 K−1, and 200 nm, 1.25 × 106 Ω−1 m−1, 0.84 W m−1 K−1, respectively. The practicality of using this optimized device to achieve ultrahigh density, ultralow energy consumption, ultrafast switching speed, low interfacial contact resistance, and high thermal reliability has also been demonstrated.

Preparation and performances of electrically conductive Nb-doped TiO2 coatings for 316 stainless steel bipolar plates of proton-exchange membrane fuel cells

The dissolution and passivation of the metal bipolar plates is one of the main problems for the commercialization of proton exchange membrane fuel cell (PEMFC). In present study, the adhesive anatase Ti1-xNbxO2 coatings are prepared on the 316 L and their corrosion behavior is also investigated in 0.1 M H2SO4 solution at 80 °C. The coatings can increase the corrosion potential of 316 L by more than 200 mVAg/AgCl. Thirty-day exposure experiment indicates that the Ti1-xNbxO2 coatings show high stability, and can inhibit effectively the corrosion of the steel. Moreover, a lower interfacial contact resistance is achieved for the Ti0.96Nb0.04O2 coating.

Bipolar plate development with additive manufacturing and protective coating for durable and high-efficiency hydrogen production

Additive manufacturing (AM) of the complex devices for energy application remains an almost unexplored area, and the harsh acidic environment also limits the application of AM parts in water splitting for hydrogen production. Here, bipolar plates (BPs), which are used to transport reactants/products and conduct electrons in proton exchange membrane electrolyzer cells (PEMECs), are printed from stainless steel (SS) with selective laser melting (SLM). Then surface treatments are employed on those BPs by thin film electroplating with Au, and the protective thin layer enables the utilization of AM SS parts to both cathode and anode sides of water electrolyzer cells and exhibits superior corrosion resistances and electronic conductivities. The Au-coated AM SS BPs deliver a low interfacial contact resistance (6.4 mΩ cm2 under 1.45 MPa) and an excellent performance in PEMECs (1.71 V at 2 A/cm2), and maintain a remarkable durability in the simulated anode environment compared with the uncoated AM SS BPs and conventional graphite BPs. This approach demonstrates the possibility of 3-dimensional printing fully integrated water electrolyzer cells at both anode and cathode sides.

CORROSION PROTECTION OF ELECTROLESS PLATING Ni-P INCLUDING TiN NANOPARTICLES FOR BIPOLAR PLATES OF PEMFCs

The Ni-P/TiN coating was used as bipolar plate by electroless plating on Ti. Surface morphology and phase structure of the coatings were characterized by SEM and XRD, respectively. Corrosion resistance of Ni-P and Ni-P/TiN coating was measured in the simulated solution of Proton exchange membrane fuel cells (PEMFCs). The interfacial contact resistance (ICR) was conducted by applied different forces. SEM images indicated that the particles of core–shell structure were formed on the surface of coating on Ti substrate. The core–shell structure was composed of TiN core and Ni-P electroless plating shell. Compared with Ni-P coatings, the Ni-P/TiN coating showed better corrosion resistance behaviors and low ICR (below 10[Formula: see text]m[Formula: see text][Formula: see text] cm[Formula: see text] under pressure of 200 N/cm[Formula: see text]. TiN particles and distribution of core–shell were in favor of the formation of coating and compact surface morphology. The good conductivity was attributed to the compact surface morphology of coating. The Ni-P/TiN coating showed excellent interfacial conductivity and good corrosion resistance at applied high potential in simulated solution of PEMFCs.

Electrochemical Properties of Niobium Modified AISI316L Stainless Steel Bipolar Plates for Direct Formic Acid Fuel Cell

AbstractTo ameliorate the corrosion resistance and surface electrical conductivity of AISI316L stainless steel (316L SS) as bipolar plates for direct formic acid fuel cell (DFAFC), a niobium diffusion layer has been successfully prepared on 316L SS substrate via the plasma surface diffusion alloying (PSDA) technique. The niobium modified AISI316L stainless steel (Nb‐316L SS) has a compact and successive niobium diffusion layer with a lower interfacial contact resistance (ICR) compared with bare 316L SS. The electrochemical behaviors of Nb‐316L SS in simulated varied anode (0.05M H2SO4 + 2 ppm HF + xM formic acid (x = 2, 5, 10 and 15) solution at 50 °C) and cathode (0.05M H2SO4 + 2 ppm HF solution at 50 °C, bubbled with air) DFAFC environments are systematically studied. The results show that the corrosion resistance of 316L SS is distinctly bettered in both anode and cathode environments of DFAFC after the PSDA modification. After 4 h potentiostatic polarization tests, the ICR of bare and Nb‐316L SS have increased at the clamping force of 140 N cm−2, but the increasing amplitude of the ICR for Nb‐316L SS is much smaller than that of bare 316L SS.

Surface coating and texturing on stainless-steel plates to decrease the contact resistance by using screen printing

Stainless steel is an attractive material for use in bipolar plates of polymer-electrolyte-membrane fuel cells, except for its high interfacial contact resistance (ICR). Inexpensive surface treatment is required to decrease the ICR. A carbonaceous conductive composite was coated on stainless-steel plate surfaces by using a screen-printing technique. A grid-like texture of the same material as the coating was also printed on the coated plate surface. The cross section showed that conductive carbon particles were well dispersed in the coating layer, which favors through-plane electrical conductivity. The coated and textured plates exhibited a much lower ICR than that of bare stainless steel. The ICR of textured plates was lower than that of coated plates under lower compaction pressures. A single cell with coated and textured bipolar plates exhibited higher power densities than that of bare stainless-steel bipolar plates.

Corrosion and interfacial contact resistance behavior of electrochemically nitrided 316L SS bipolar plates for proton exchange membrane fuel cells

In the present investigation, electrochemically nitrided surface was developed on 316L stainless steel (SS) through potentiostatic method using an aqueous solution containing 0.1 M HNO3 and 0.5 M KNO3 at room temperature. The formation of nitrides was confirmed by X - ray photoelectron spectroscopy (XPS) and the formed nitrides existed in the form of mixed nitrides viz, CrN, Cr2N and nitrogen incorporated oxides (Cr-O-N). The corrosion behavior of untreated and nitrided SS was studied in 0.5 M H2SO4 and 2 ppm of HF. The untreated and nitrided SS showed decrease in impedance value with increasing potential from OCP (Open Circuit Potential) to proton exchange membrane fuel cell (PEMFC) anode and cathode environments and nitrided SS exhibited comparatively higher impedance values at each potential. The lower passive current density and lower metal ions concentration released for nitrided SS in both PEMFC anode and cathode environments indicated higher corrosion resistance. Before polarization, the interfacial contact resistance (ICR) value of nitrided SS matched well with Department of Energy's (DOE's) required value. After polarization, the lower ICR values for nitrided SS indicate enhanced electrical conductivity.

Defect modification to improve field emission of ZnO NRs by coating ultrathin Pt films

Ultrathin platinum (Pt) films are coated on the surface of ZnO NRs grown on Fe alloy substrates and display excellent field emission performance with the turn-on field Eto as low as 0.40 V/μm and the threshold field Ethr down to 2.62 V/μm. By coating ultrathin Pt films on the surface of the ZnO NRs, this not only helps to modify the linear defects on the outer surface of ZnO NRs, but also suppresses random electron emission along the defect directions. At an external electric field, a large amount of electrons are transported to the top of ZnO NRs where a highly localized electric field is caused, which results in enhanced field emission. Besides, ZnO NRs grown on Fe alloy substrates have a low interfacial contact resistance and intend to reduce the barrier between the substrate and the ZnO. Meanwhile, metal Pt films can help to obtain emitting centers that ensure highly conductive paths for the electrons from the ZnO NRs towards the vacuum, which effectively decrease the barrier between the ZnO and the vacuum. Finally, a schottky contact of Fe-ZnO and matched Fermi levels of ZnO-Pt contribute to the enhanced current emission efficiency. This work may help the development of the practical electron sources and advanced devices based on ZnO field emitters.

Requirements and testing methods for surfaces of metallic bipolar plates for low-temperature PEM fuel cells

To reduce emissions and to substitute combustion engines automotive manufacturers, legislature and first users aspire hydrogen fuel cell vehicles. Up to now the focus of research was set on ensuring functionality and increasing durability of fuel cell components. Therefore, expensive materials were used. Contemporary research and development try to substitute these substances by more cost-effective material combinations. The bipolar plate is a key component with the greatest influence on volume and mass of a fuel cell stack and they have to meet complex requirements. They support bending sensitive components of stack, spread reactants over active cell area and form the electrical contact to another cell. Furthermore, bipolar plates dissipate heat of reaction and separate one cell gastight from the other. Consequently, they need a low interfacial contact resistance (ICR) to the gas diffusion layer, high flexural strength, good thermal conductivity and a high durability. To reduce costs stainless steel is a favoured material for bipolar plates in automotive applications. Steel is characterized by good electrical and thermal conductivity but the acid environment requires a high chemical durability against corrosion as well. On the one hand formation of a passivating oxide layer increasing ICR should be inhibited. On the other hand pitting corrosion leading to increased permeation rate may not occur. Therefore, a suitable substrate lamination combination is wanted. In this study material testing methods for bipolar plates are considered.

TaNX coatings deposited by HPPMS on SS316L bipolar plates for polymer electrolyte membrane fuel cells: Correlation between corrosion current, contact resistance and barrier oxide film formation

Tantalum nitride (TaNx) coatings deposited by High Power Pulsed Magnetron Sputtering (HPPMS) technology at different N2-to-Ar ratios; i.e. 0, 0.25, 0.625 and 1, corresponding to different N/Ta atomic ratio in the film, were investigated as suitable candidates to improve SS316L bipolar plate's performance and durability for polymer electrolyte membrane fuel cells (PEMFC). The corrosion resistance of TaNx coatings was evaluated by potentiodynamic and potentiostatic tests carried out under different cathodic potentials (0.8 VSHE, 1 VSHE, and 1.4 VSHE), electrolyte acidities (pH 3 and pH 6) and test durations (5 and 180 min) in order to mimic real fuel cell operation conditions. Corrosion currents observed for all TaNx coatings were relatively low (1–15 μA cm−2) regardless of N/Ta atomic ratio and applied variable testing parameters. However, considerable differences in Interfacial Contact Resistance (ICR) values were observed after polarization, depending on tested coating material and conditions. The ICR increased with increasing applied potential, electrolyte pH and test duration for the substrate and all TaNx coatings. Ta coated SS316L exhibited lower ICR (42–82 mΩ cm2) values than the uncoated SS316L (47–278 mΩ cm2) at potentials higher than 1 VSHE. A significant rise in ICR was detected for all nitride TaN films after 180 min of polarization at 1.4 VSHE in pH 3, showing ICR values from 362 to 538 mΩ cm2, depending on N2-to-Ar ratio. Ta coated SS316L polarized at 0.8 VSHE showed low ICR values, around 25–37 mΩ cm2. Auger electron spectroscopy (AES) was performed before and after polarization to investigate barrier oxide film formation kinetics. AES study revealed the growth of different composition and thickness oxide layers for each TaNx coating, exposing the great importance of coating composition on subsequent type of oxide formation. Barrier oxide layer characteristics have been found to dominate the ICR response of TaNx films after polarization.

Characterization and corrosion resistance of TiZr coating on SS304 stainless steel using cathodic arc evaporation techniques

In this study, an alternating titanium and zirconium (TiZr) nano-composite layer is deposited on a SS304 stainless steel surface to improve the corrosion resistance of bare SS304 in an acid environment with and without F ions as well as in a NaCl salt solution using cathodic arc evaporation techniques. The microstructures of this TiZr coating are studied and correlated with corrosion resistance. The corrosion resistance of a TiN/ZrN coating, which has an alternating titanium nitride/zirconium nitride (TiN/ZrN) multilayer, is compared with the corrosion resistance of the TiZr coating. The results show that the TiZr coating (layer thickness of 3.66μm) has a nano-composite structure consisting of alternating Ti and Zr layers with a hexagonal closest-packed (hcp) arrangement. The corrosion rates of SS304 coated with a TiZr layer are much lower than those of uncoated SS304 in H2SO4 with and without F ions as well as in the NaCl salt solution. Additionally, the corrosion resistance of our TiZr coating is better than that of TiN/ZrN, CrN, TiN, TiN/CrN and CrN/Ti coatings and a bulk Ti25Zr75 alloy. The excellent corrosion resistance of the TiZr coating is attributed to the alternating Ti and Zr nano-composite structure with an hcp arrangement, which provides an effective impediment to active corrosive ions during anodic dissolution. Furthermore, the TiZr coating has lower interfacial contact resistance than the SS304, even after corrosion in H2SO4 with F ions, and it offers less surface resistance than the TiN/ZrN coating. This makes the TiZr coating a better protective coating for SS304 bipolar plates.

Performance of a PEM Fuel Cell Using Electroplated Ni–Mo and Ni–Mo–P Stainless Steel Bipolar Plates

The performance and durability of 316L stainless steel bipolar plates (BPP) electroplated with Ni–Mo and Ni–Mo–P coatings are investigated in a proton exchange membrane fuel cell (PEMFC), using a commercial Pt/C Nafion membrane electrode assembly (MEA). The effect of the BPP coatings on the electrochemical performance up to 115 h is evaluated from polarization curves, cyclic voltammetry and electrochemical impedance spectroscopy together with interfacial contact resistance (ICR) measurements between the coatings and the gas diffusion layer. The results show that all the coatings decrease the ICR in comparison to that of uncoated 316L BPP. The Ni-Mo coated BPP shows a low and stable ICR and the smallest effects on MEA performance, including catalyst activity/usability, cathode double layer capacitance, and membrane and ionomer resistance build up with time. After electrochemical evaluation, the BPPs as well as the water effluents from the cell are examined by Scanning Electron Microscopy, Energy Dispersive and Inductively Coupled Plasma spectroscopies. No significant degradation of the coated surface or enhancement in metal release is observed. However, phosphorus addition to the coating does not show to improve its properties, as deterioration of the MEA and consequently fuel cell performance losses is observed.

Site-Selective, Low-Loading, Au Nanoparticle–Polyaniline Hybrid Coatings with Enhanced Corrosion Resistance and Conductivity for Fuel Cells

Ultralow loading of Au nanoparticles (0.038 mg cm–2) and a polyaniline hybrid coating (AuNP-PANI) were deposited on stainless steel (SS316L) coupons. The unique two-step approach utilizing electrochemical deposition via cyclic voltammetry enabled growth of AuNPs in the fibrous PANI micropores thereby achieving enhanced surface coverage of SS316L and minimizing substrate corrosion via blocking of pores. The hybrid coatings revealed significantly low interfacial contact resistance values of 16.6 mΩ cm2 (achieving the US DOE 2017 targets). Potentiodynamic tests revealed the excellent corrosion resistance of AuNP-PANI hybrid coatings with a corrosion potential of 0.61 VSHE, which is positively shifted by 790 and 390 mV as compared to bare SS316L and PANI-SS316L, respectively. The corresponding potentiostatic corrosion current density of AuNP-PANI was reduced to 0.63 μA/cm2 from 2.28 and 0.65 μA/cm2 for bare SS316L and PANI-SS316L samples, respectively, thereby providing excellent stability in the cathodic pol...

Pb-free front-contact silver pastes with SnO[sbnd]P2O5 glass frit for crystalline silicon solar cells

We developed a new Pb-free Ag paste with a SnOP2O5 glass frit for front contact electrodes of crystalline silicon solar cells. First, we synthesized SnOP2O5 glass frits with various compositions, whose glass transition temperatures were 225–245 °C, by using a melt-quenching method. It was experimentally verified that the glass component SnO etched through the silicon nitride anti-reflection coating on the Si emitter. Then, four kinds of Ag pastes with various SnOP2O5 glass frits were prepared, screen-printed on a Si emitter, and fired to fabricate solar cells. The composition of the SnOP2O5 glass frit affected the surface and interfacial morphology and microstructure of sintered Ag grids, which played an important role in the series resistance and photovoltaic properties of the solar cells. It was worth noting that the cells fabricated with SnO-based Ag pastes revealed no glass layer at the interface between the Ag grids and Si emitter. This differed from cells fabricated with Ag pastes containing Pb- or Bi-based glass frits. The highest efficiency of 7.2% was achieved for cells fabricated with the Ag paste containing 67SnO33P2O5 (mol%) glass frit at a firing temperature of 950 °C and a time of 5 min. This was because this Ag paste possessed the densest structure and lowest interfacial contact resistance.