The transition to non-platinum group metal (PGM) electrocatalysts for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs) is central to achieving sustainable and cost-effective energy conversion. However, the continued widespread use of platinum counter electrodes in electrochemical testing introduces a critical artefact, namely, platinum dissolution, migration through the electrolyte and redeposition onto the working electrode. This potentially skews performance metrics and undermines claims of ‘platinum-free’ sustained ORR activity. This study systematically investigates this issue using a model nitrogen-doped carbon electrocatalyst with inherently low catalytic activity, allowing facile observation of small performance improvements that may be difficult to separate in high-performance catalysts. Platinum wire and graphite rod counter electrodes are compared under load cycling and start-stop conditions in both acidic and alkaline media over 60,000 potential cycles. We demonstrate that platinum contamination from the counter electrode significantly enhances ORR activity and slows performance degradation, effects which are absent when a graphite counter electrode is used. Transmission electron microscopy (TEM) confirms platinum electrodeposition on the working electrode. These findings challenge prevailing experimental protocols and establish the graphite counter electrode as essential for accurate benchmarking of non-PGM catalysts. The work delivers a clear methodological clarification with broad implications for electrocatalyst development and validation.
Electrochemiluminescence (ECL) is a highly sensitive detection technique; however, its inherently low selectivity is a significant challenge in analytical and sensing applications. In this study, we developed a system for the specific determination of the pharmaceutical bromhexine (BH). In this system, ECL was combined with a molecularly imprinted polymer (MIP) capable of molecular recognition. A BH-template-based MIP-modified electrode, synthesized by electrolytic polymerization, was prepared. Interestingly, the MIP-modified electrode robustly immobilized the template molecule via peroxidation during electrolytic synthesis. The sensitivity was approximately three times that without further oxidation. X-ray absorption fine structure measurements were performed using synchrotron radiation to characterize interactions between the analyte and the polymer. From the results, a complex mechanism involving hydrogen bonding, π-π interactions, and halogen-π interactions was inferred between the analytical chemical species and the polymer. The fabricated MIP-modified electrode was applied to determine BH in commercially available pharmaceuticals, prescription drugs, and biological urine samples. The results were compared with those from liquid chromatography-mass spectrometry. This system shows potential for development into a selective sensor.
The discovery of superconductivity in pressurized Ruddlesden-Popper (RP) nickelates has provided new perspectives on the mechanism of high-temperature superconductivity. Up to now, most experiments concentrated on the lanthanum-related RP phase, so the discovery of new superconducting RP nickelates is highly desirable to reveal their generality. Here we report the observation of superconductivity in Pr4Ni3O10 single crystals above 10 GPa, achieving a maximum Tc of 39 K without saturation, significantly exceeding the value of 25–30 K of La4Ni3O10. Ultrasensitive magnetic susceptibility measurements under high pressure indicate bulk superconductivity with appreciable superconducting volume fractions. Unlike La4Ni3O10, the electronic structure of the high-pressure phase of Pr4Ni3O10 exhibits a dramatic metallization of the σ-bonding band consisting of three d_z^2 orbitals and van Hove singularity of coupled bands of d_x^2-y^2 orbitals near the Fermi level, similar to La3Ni2O7. These findings reveal some generic features of both crystal and electronic structures for high-temperature superconductivity in nickelates and multi-layer cuprates.
The synergistic integration of two-electron oxygen reduction reaction (2e-ORR) and water oxidation reaction (2e-WOR) enables efficient overall electrosynthesis of hydrogen peroxide (H2O2). However, the rational development of effective bifunctional electrocatalysts remains challenging. Herein, a nitrogen-bridged Ni-Sn dual-atom catalyst embedded within a conductive metal-organic framework (NiSn-HITP) is developed, which enables efficient overall electrosynthesis of H2O2 through site-specific synergistic catalysis in the separated half-reactions. Atomically dispersed Ni and Sn sites endow the catalyst with outstanding individual performance, achieving a Faradaic efficiency for H2O2 (FEH2O2) of up to 98.8 % in ORR and 66.9 % in WOR. Notably, when employed as a bifunctional catalyst in a single electrolytic cell, NiSn-HITP delivers an impressive overall FEH2O2 of 171.5 % with a maximum H2O2 yield rate of 9.1 mol gcat-1 h-1. Theoretical calculations reveal that Ni and Sn act as the primary active sites for the 2e-WOR and 2e-ORR, respectively, thus enabling complementary dual-site catalysis. More importantly, the tailored electronic structure, modulated by orbital coupling, promotes both the efficiency and selectivity of H2O2 electrosynthesis. In-situ Fourier-transform infrared spectroscopy further elucidates the reaction pathways. This work offers a new design strategy for bifunctional electrocatalysts, paving the way for practical applications of green H2O2 electrosynthesis.
The fragile-to-strong transition in supercooled water, where the relaxation dynamics shift from non-Arrhenius to Arrhenius behaviour, has been hypothesized to explain its anomalous dynamic properties. However, this transition remains unresolved, as previous ultrafast experimental studies of bulk water dynamics were limited to temperatures far from the proposed transition due to rapid crystallization. Here we use an infrared laser pump and an ultrashort X-ray probe to measure the structural relaxation in micrometre-sized water droplets, evaporatively cooled at timescales ranging from femtoseconds to nanoseconds. Our experimental data show a dynamic crossover at around 233 K. Below this temperature, the relaxation dynamics deviate from simple power-law fits and follow a shallower temperature dependence. Molecular dynamics simulations successfully reproduce our findings.
