Polymer electrolyte membrane fuel cells (PEMFCs) expect a promising future in addressing the major problems associated with production and consumption of renewable energies and meeting the future societal and environmental needs. Design and fabrication of new proton exchange membranes (PEMs) with high proton conductivity and durability is crucial to overcome the drawbacks of the present PEMs. Acid-doped polybenzimidazoles (PBIs) carry high proton conductivity and long-term thermal, chemical, and structural stabilities are recognized as the suited polymeric materials for next-generation PEMs of high-temperature fuel cells in place of Nafion® membranes. This paper aims to review the recent developments in acid-doped PBI-based PEMs for use in PEMFCs. The structures and proton conductivity of a variety of acid-doped PBI-based PEMs are discussed. More recent development in PBI-based electrospun nanofiber PEMs is also considered. The electrochemical performance of PBI-based PEMs in PEMFCs and new trends in the optimization of acid-doped PBIs are explored.
Perovskite solar cells (PSCs) have captured the attention of the global energy research community in recent years by showing an exponential augmentation in their performance and stability. The supremacy of the light-harvesting efficiency and wider band gap of perovskite sensitizers have led to these devices being compared with the most outstanding rival silicon-based solar cells. Nevertheless, there are some issues such as their poor lifetime stability, considerable J–V hysteresis, and the toxicity of the conventional constituent materials which restrict their prevalence in the marketplace. The poor stability of PSCs with regard to humidity, UV radiation, oxygen and heat especially limits their industrial application. This review focuses on the in-depth studies of different direct and indirect parameters of PSC device instability. The mechanism for device degradation for several parameters and the complementary materials showing promising results are systematically analyzed. The main objective of this work is to review the effectual strategies of enhancing the stability of PSCs. Several important factors such as material engineering, novel device structure design, hole-transporting materials (HTMs), electron-transporting materials (ETMs), electrode materials preparation, and encapsulation methods that need to be taken care of in order to improve the stability of PSCs are discussed extensively. Conclusively, this review discusses some opportunities for the commercialization of PSCs with high efficiency and stability.
This article reports a comparative experimental study of the hygroscopic and mechanical behaviors of electrospun polybenzimidazole (PBI) nanofiber membranes and solution-cast PBI films. Aselectrospun nonwoven PBI nanofiber mats (with the nanofiber diameter of ~250 nm) were heat-pressed under controlled temperature, pressure and duration for the study; lab-made solution-cast PBI films and commercially available PBI films (the PBI Performance Product Inc., Charlotte, NC ) were used as the control samples. Thermogravimetric and micro-tensile tests were utilized to characterize the hygroscopic (moisture absorption) and mechanical properties of the PBI nanofiber membranes at varying heat-pressing conditions, which were further compared to those of solution-cast PBI films. Experimental results indicated that the PBI nanofiber membranes carried slightly higher thermal stability and less hygroscopic properties than those of solution-cast PBI films. In addition, heat-pressing conditions significantly influenced the mechanical properties of the resulting PBI nanofiber membranes. The stiffness and tensile strength increase with increasing either the heat-pressing pressure or duration, and relevant mechanisms were explored. The present study provides a rational understanding of the hygroscopic and mechanical behaviors of electrospun This article is protected by copyright. All rights reserved. This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
Proton exchange membrane fuel cells (PEMFCs) cathode catalysts’ robustness is one of the primary factors determining its long-term performance and durability. This work presented a new class of corrosion-resistant catalyst, Magnél TiO2 supported Pt (Pt/Ti9O17) composite, synthesized. The durability of a Pt/Ti9O17 cathode under the PEMFC operating protocol was evaluated and compared with the state-of-the-art Pt/C catalyst. Like Pt/C, Pt/Ti9O17 exhibited exclusively 4e- oxygen reduction reaction (ORR) in the acidic solution. The accelerated stress tests (AST) were performed using Pt/Ti9O17 and Pt/C catalysts in an O2-saturated 0.5 M H2SO4 solution using the potential-steps cycling experiments from 0.95 V to 0.6 V for 12,000 cycles. The results indicated that the electrochemical surface area (ECSA) of the Pt/Ti9O17 is significantly more stable than that of the state-of-the-art Pt/C, and the ECSA loss after 12,000 potential cycles is only 10 ± 2% for Pt/Ti9O17 composite versus 50 ± 5% for Pt/C. Furthermore, the current density and onset potential at the ORR polarization curve at Pt/C were significantly affected by the AST test. In contrast, the same remained almost constant at the modified electrode, Pt/Ti9O17. This demonstrated the excellent stability of Pt nanoparticles supported on Ti9O17.
The durability of catalysts in polymer electrolyte membrane fuel cells (PEMFCs) is an important issue that must be addressed before their commercialization since catalyst durability directly reflects the life and cost of fuel cell power-generation systems [1]. Although many factors could play a role in the mechanism of catalyst degradation, the major contributors are believed to be i) dissolution of Pt and re-deposition (Ostwald ripening), ii) coalescence via crystal migration, and iii) detachment of Pt particles from the carbon support [2]. Among these, Pt detachment is strongly affected by the corrosion of the carbon support materials. Conventional carbon blacks, such as Vulcan XC72, are superior catalyst-support materials because of their cost and physicochemical properties. However, carbon is not stable based on thermodynamic considerations under the cathode conditions in a PEMFC: C + 2H2O → CO2 + 4H+ + 4e− E0 = 0.207 V vs. RHE Although this reaction proceeds slowly at potentials <0.8 V in a PEMFC [3], corrosion reactions are significantly accelerated under high potential conditions. Therefore, alternative catalyst-support materials that are highly oxidation-resistant are necessary. In order to improve the stability of the catalyst support, considerable work has been done over the past few decades on non-carbon support materials [4]. In this presentation, we have focused on oxygen-deficient, sub-stoichiometric titanium oxide (TinO2n−1, known as Magnéli phase) as a potential oxidation-resistant cathode catalyst support in PEFCs. This leads to improving specific activity for the oxygen reduction reaction (ORR) due to the formation of Pt–Ti alloy particles on the TiOx support, as well as the improve dispersion of Pt due to the deposition of smaller catalyst particles. The Magnéli phase Ti9O17 is synthesized and characterized (Fig. 1) by XRD. The Pt/Ti9O17 will be synthesized, and the ORR activity and stability will be investigated. A comparative study will be performed to those of a conventional Pt/C catalyst. References: Chem. Rev., 107, 3904 (2007) Top. Catal., 46,285(2007) ECS Trans., 1 (8), 3 (2006) J. Mater. Chem., 19, 46 (2009) Figure 1
We report the rational fabrication and structural, thermal, mechanical, and electrochemical characterization of a new type of intermediate-temperature (IT) polymer-inorganic composite (PIC) proton exchange membranes (PEMs) that are made of cerium ultraphosphate (CeP5O14—CUP) as the solid-state proton conductor composited with a high-temperature (HT) polybenzimidazole (PBI) as the polymeric binder. Flexible PBI-CUP PIC membranes with the thickness of ~135 μm and CUP mass fraction of up to 75 % were prepared by solution-casting without additional acid-doping (e.g., phosphoric acid). The proton conductivity of the fabricated IT-PIC-PEMs was up to 5.80 × 10-2 S cm-1 as measured from a prototype IT PEM fuel cell (PEMFC) operated at 200°C in the humidified hydrogen and air environment. This type of IT-PIC-PEMs also demonstrated sufficient mechanical strength and flexibility, excellent thermal stability (up to 350°C), and very good durability of the proton conductivity (within the test duration of 500 h). The present experimental study shows the promising future of the IT-PIC-PEMs for applications in various IT electrochemical processes including IT-PEMFCs, IT-electrolyzers, etc.
Conventional ammonia production consumes significant energy and causes enormous carbon dioxide (CO2) emissions globally. To lower energy consumption and mitigate CO2 emissions, a facile, environmentally friendly, and cost-effective one-pot method for the synthesis of a ruthenium-based nitrogen reduction nanocatalyst has been developed using reduced graphene oxide (rGO) as a matrix. The nanocatalyst synthesis was based on a single-step simultaneous reduction of RuCl3 into ruthenium-based nanoparticles (Ru-based NPs) and graphene oxide (GO) into rGO using glucose as the reducing agent and stabilizer. The obtained ruthenium-based nanocatalyst with rGO as a matrix (Runano-based/rGO) has shown much higher catalytic activity at lower temperatures and pressures for ammonia synthesis than conventional iron catalysts. The rGO worked as a promising promoter for the electrochemical synthesis of ammonia due to its excellent electrical and thermal conductivity. The developed Runano-based/rGO nanocatalyst was characterized using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), ultraviolet–visible (UV–vis) absorption spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), inductively coupled plasma mass spectrometry (ICP-MS), and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the size of the Ru-based NPs on the surface of rGO was 1.9 ± 0.2 nm and the ruthenium content was 25.03 wt %. Bulk electrolysis measurements were conducted on thin-layer electrodes at various cathodic potentials in a N2-saturated 0.1 M H2SO4 electrolyte at room temperature. From the chronoamperometric measurements, the maximum faradic efficiency (F.E.) of 2.1% for ammonia production on the nanostructured Runano-based/rGO electrocatalyst was achieved at a potential of −0.20 V vs reversible hydrogen electrode (RHE). This electrocatalyst has attained a superior ammonia production rate of 9.14 μg·h–1·mgcat. –1. The results demonstrate the feasibility of reducing N2 into ammonia under ambient conditions and warrant further exploration of the nanostructured Runano-based/rGO for electrochemical ammonia synthesis.
Corrosion is defined as the destruction of metals and alloys by chemical or electrochemical reaction with its environment. The corrosion occurs because of the normal trend of metals to come back to their thermodynamically stable native state. Corrosion cannot be avoided, but it can be controlled and prevented by using suitable methods like cathodic protection, anodic protection, metallic coating, alloying and using inhibitors, etc. Of these, the application of inhibitors reduces the aggressiveness of the corrosive and unsafe aqueous surroundings and preventing the metal and alloy from corrosion by forming a protective layer over the metal surface. The corrosion behavior of stainless steel and other metals in seawater has been studied by many researchers [1-2]. Stainless steels (316L) have been used successfully in many applications in the marine environment. 316L is considered to be one of the most resistant of stainless steel under marine environments, and it has excellent mechanical properties at elevated temperatures and easy fabricability. It is an important structural material for many industrial units, especially the desalination plants. 316L is the most likely candidate for saline environment applications due to their excellent corrosion resistance. The present work was undertaken to study the corrosion behavior of SS 316L metal in different mediums such as Seawater and calcium chloride (Fig. 1) solution by polarization study. The effect of oxygen or air in the electrolyte solution will also be investigated. Corrosion parameters such as corrosion potential, corrosion current, linear polarization resistance, and corrosion rate will be compared and presented in the meeting. References [1] Baoping Cai et al., Corrosion Science 52 (2010) 3235–3242 [2] Yong Cui et al., Water Research 88 (2016) 816-825 Figure 1
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