Search

Platinum (Pt)‐based electrocatalysts are considered benchmark materials for the hydrogen evolution reaction (HER) in acidic solution. However, widespread use is limited by the high price of Pt. Tuning the Pt morphology to increase the catalytic surface area for the same mass loading is therefore essential to increase its utilization. Herein, single Ti3C2Tz flakes were deposited by electrophoresis onto a carbon‐fiber gas diffusion layer, after which Pt nanostructures were selectively deposited onto the Ti3C2Tz flakes by pulse electrodeposition. It was observed that the pulse on‐time (ton) and duration had a significant effect on the morphology and activity of the composite electrode towards HER. Flower‐like and spherical morphologies were produced at long and short values of ton, respectively. As‐synthesized electrocatalysts were studied for HER in 0.5 M sulfuric acid (H2SO4). The catalyst with the lowest Pt loading (10 μg/cm2), exhibited outstanding HER performance. It attained a current density of 10 mA/cm2 at an overpotential of 38 mV, close to that of commercial carbon supported platinum (Pt/C, Vulcan XC). This catalyst exhibited a high turnover frequency (23.9 H2 s−1 @ 100 mV), small Tafel slope (41 mV/dec), and high mass‐specific activity (2.45 A/mgPt @ 100 mV). [ABSTRACT FROM AUTHOR]

The feasibility of using argon‐atomized QT 17‐4+ stainless steel powder for directed energy deposition (DED) additive manufacturing is studied. The QT 17‐4+ steel is a novel martensitic steel designed based on the compositional modification of the standard 17‐4 precipitation‐hardened (PH) stainless steel. This modification aims to achieve better mechanical properties of as‐deposited components compared to the heat‐treated wrought 17‐4PH steel. In this study, QT 17‐4+ steel powder is used for DED, for the first time. The influence of laser power, laser scan speed, powder feed rate, and hatch overlap on the density is studied. The central composite design is used to determine the experimental matrix of these factors. The response surface methodology is used to obtain the empirical statistical prediction model. Both columnar and equiaxed parent austenite grain structures are observed. X‐ray diffraction analyses reveal a decrease in the percentage of retained austenite from 19% in the powder to 5% after DED. The microhardness of the DED processed sample in the as‐deposited state is slightly higher than that of wrought 17‐4PH steel either solution‐annealed or H900‐aged. A higher 0.2% yield strength, a lower ultimate tensile strength, and lower elongation are observed for the vertically printed test sample, when compared to the horizontal one. [ABSTRACT FROM AUTHOR]

MXenes have gained significant attention, particularly Ti3C2Tz, as materials with favorable properties for energy storage and conversion applications. The overwhelming majority of electrochemical durability studies are based on durability in the hydrogen evolution window, well below the reversible hydrogen electrode where degradation via electrochemical oxidation is less relevant. Consequently, few strategies have been put forward to protect Ti3C2Tz at higher potentials and widen their applicability to electrochemical systems. Here, the electrochemical degradation of pristine Ti3C2Tz and tantalum (Ta)‐substituted (Ti0.95Ta0.05)3C2Tz is reported. X‐ray photoelectron spectroscopy and electron microscopy revealed that pristine and Ta‐doped MXene went through entirely different degradation mechanisms, and that these mechanisms are driven by electrochemical, rather than chemical effects. Density functional theory is used to explain the role of Ta doping with respect to the binding of oxygen and the formation of metal oxide phases. The influence of the degradation mechanism is observed by accelerated stress tests and anode reversal tests on a polymer electrolyte membrane fuel cell. Therefore, the substitution of titanium (Ti) with other oxyphilic metals in Ti3C2Tz may be an effective route to improve the durability of the otherwise fragile MXene phase. [ABSTRACT FROM AUTHOR]