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