Cerium-Based Perovskite Mixed Metal Oxide as the Radical Scavenger for PEM Fuel Cells Operating under Low Humidity Conditions

Rare Earth Ce/CeO2 Electrocatalysts: Role of High Electronic Spin State of Ce and Ce3+/Ce4+ Redox Couple on Oxygen Reduction Reaction

With unique 4f electronic shells, rare earth metal-based catalysts have been attracting tremendous attention in electrocatalysis, including oxygen reduction reaction (ORR). In particular, atomically dispersed Ce/CeO2-based catalysts have been explored extensively due to several unique features. This review article provides a comprehensive understanding of (i) the significance of the effect of Ce high-spin state on ORR activity enhancement on the Pt and non-pt electrocatalysts, (ii) the spatially confining and stabilizing effect of ceria on the generation of atomically dispersed transition metal-based catalysts, (iii) experimental and theoretical evidence of the effect of Ce3+ ↔ Ce4+ redox pain on radical scavenging, (iv) the effect of the Ce 4f electrons on the d-band center and electron transfer between Ce to the N-doped carbon and transition metal catalysts for enhanced ORR activity, and (v) the effect of Pt/CeO2/carbon heterojunctions on the stability of the Pt/CeO2/carbon electrocatalyst for ORR. Among several strategies of synthesizing Ce/CeO2 electrocatalysts, the metal-organic framework (MOF)-derived catalysts are being perused extensively due to the tendency of Ce to readily coordinate with O- and N-containing ligands, which upon undergoing pyrolysis, results in the formation of high surface area, porous carbon networks with atomically dispersed metallic/clusters/nanoparticles of Ce active sites. This review paper provides an overview of recent advancements regarding Ce/CeO2-based catalysts derived from the MOF precursor for ORR in fuel cells and metal-air battery applications and we conclude with insights into key issues and future development directions.

Facile stoichiometric interfacial surface bonded cerium oxide and graphene oxide heterostructure for efficient electrochemical non-enzymatic detection of dopamine

Emerging technology in the new era of sensors to detect and quantify neurological reaction-based research has demanded the development of sensors for the neurotransmitter dopamine (DA). In recent decades, electrochemical sensors have offered rapid and sensitive detection of DA, but the presence of interfering compounds, such as uric acid (UA) and ascorbic acid (AA), poses a great threat to the development of DA sensors. Additionally, reusing traditional methods leads to challenges like prolonged preparation and expensive instruments. This research work offers a nanohybrid two-dimensional (2D) paper-like graphene oxide (GO) and three-dimensional (3D) cerium oxide nanosphere (CeONS) heterostructure composite (G-CeONS) created via stoichiometric synthesis for the non-enzymatic detection of DA oxidation in the presence of other complex biological compounds. The constructed G-CeONS nanohybrid composite enables enhanced selectivity and sensitivity towards DA detection through its interfacial engineering. The heterostructure formation of a 2D nanosheet draped over 3D nanospheres exhibits a wide linear concentration range of 100-30 800 nM with a low detection limit of 20.98 nM. Further investigation of the real-time performance on human saliva and DA injections afforded prominent results. In addition, the synergetic effect of G-CeONS improves DA detection accuracy and reliability towards enabling transformational neurochemical and medicinal applications.

Influence of Oxygen Vacancies Introduced via Acceptor (Gadolinium) Doping to the Pseudocapacitive Properties of Nano-Sized Cerium Oxide

The voluntary introduction of defects can be considered an effective strategy for enhancing the electrochemical properties of metal oxide electrodes. In this study, the enhanced pseudocapacitive properties of an acceptor (Gd) doped cerium oxide nanoparticle-a sustainable metal oxide with low environmental and human toxicity-are investigated in depth using ex situ X-ray photoemission spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Interestingly, with 15 at% Gd doping (15GDC), the specific capacitance of the nanoparticles measured at 1 A g-1 enhanced to 547.8 F g-1, which is fivefold higher than undoped CeO2 (98.7 F g-1 at 1 A g-1). The rate-dependent capacitance is also improved for 15GDC, which showed a 31.0% decrease in the specific capacitance upon a tenfold increase in the current density, while CeO2 showed a 49.9% decrease. The enhanced electrochemical properties are studied in depth via ex situ XPS and EIS analysis, which revealed that the oxygen vacancies at the surface of the nanoparticles played important roles in enhancing both the specific capacitance and the high-rate performance of 15GDC by acting as the active site for pseudocapacitive redox reaction and allowing fast diffusion of oxygen ions at the surface of 15GDC nanoparticles.

Enhancing Performance and Stability of High-Temperature Proton Exchange Membranes through Multiwalled Carbon Nanotube Incorporation into Self-Cross-Linked Fluorenone-Containing Polybenzimidazole

Addressing critical challenges in enhancing the oxidative stability and proton conductivity of high-temperature proton exchange membranes (HT-PEMs) is pivotal for their commercial viability. This study uncovers the significant capacity of multiwalled carbon nanotubes (MWNTs) to absorb a substantial amount of phosphoric acid (PA). The investigation focuses on incorporating long-range ordered hollow MWNTs into self-cross-linked fluorenone-containing polybenzimidazole (FPBI) membranes. The absorbed PA within MWNTs and FPBI forms dense PA networks within the membrane, effectively enhancing the proton conductivity. Moreover, the exceptional inertness of MWNTs plays a vital role in reinforcing the oxidation resistance of the composite membranes. The proton conductivity of the 1.5% CNT-FPBI membrane is measured at 0.0817 S cm-1 at 160 °C. Under anhydrous conditions at the same temperature, the power density of the 1.5% CNT-FPBI membrane reaches 831.3 mW cm-2. Notably, the power density remains stable even after 200 h of oxidation testing and 250 h of operational stability in a single cell. The achieved power density and long-term stability of the 1.5% CNT-FPBI membrane surpass the recently reported results. This study introduces a straightforward approach for the systematic design of high-performance and robust composite HT-PEMs for fuel cells.

Mn Single-Atom Tuning Fe-N-C Catalyst Enables Highly Efficient and Durable Oxygen Electrocatalysis and Zinc-Air Batteries

Fe-N-C catalyst is one of most promising candidates for oxygen electrocatalysis reaction in zinc-air batteries (ZABs), but achieving sustained high activity is still a challenging issue. Herein, we demonstrate that introducing Mn single atoms into Fe-N-C (Mn1@Fe-N-C/CNTs) enables the realization of highly efficient and durable oxygen electrocatalysis performance and application in ZABs. Multiple characterizations confirm that Mn1@Fe-N-C/CNTs is equipped with Mn-N2O2 and Fe-N4 sites and Fe nanoparticles. The Mn-N2O2 sites not only tune the electron structure of Fe-Nx sites to enhance intrinsic activity, but also scavenge the attack of radicals from Fe-Nx sites for improvement in ORR durability. As a result, Mn1@Fe-N-C/CNTs exhibits enhanced ORR performance to traditional Fe-N-C catalysts with high E1/2 of 0.89 V vs reversible hydrogen electrode (RHE) and maintains ORR activity after 15 000 CV. Impressively, Mn1@Fe-N-C/CNTs also presents excellent OER activity and the difference (ΔE) between E1/2 of ORR and OER potential at 10 mA cm-2 (Ej10) is only 0.59 V, outperforming most reported catalysts. In addition, the maintainable bifunctional activity of Mn1@Fe-N-C/CNTs is demonstrated in ZABs with almost unchanged cycle voltage efficiency up to 200 h. This work highlights the critical role of Mn single atoms in enhancing ORR activity and stability, promoting the development of advanced catalysts.