Photodetection over a broad spectral range is crucial for optoelectronic applications such as sensing, imaging, and communication. Herein, a high‐performance ultra‐broadband photodetector based on PdSe2 with unique pentagonal atomic structure is reported. The photodetector responds from visible to mid‐infrared range (up to ≈4.05 µm), and operates stably in ambient and at room temperature. It promises improved applications compared to conventional mid‐infrared photodetectors. The highest responsivity and external quantum efficiency achieved are 708 A W−1 and 82 700%, respectively, at the wavelength of 1064 nm. Efficient optical absorption beyond 8 µm is observed, indicating that the photodetection range can extend to longer than 4.05 µm. Owing to the low crystalline symmetry of layered PdSe2, anisotropic properties of the photodetectors are observed. This emerging material shows potential for future infrared optoelectronics and novel devices in which anisotropic properties are desirable.

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Nitrogen-doped porous carbon nanospheres (PCNs) with a high surface area were prepared by chemical activation of nonporous carbon nanospheres (CNs). CNs were obtained via carbonization of polypyrrole nanospheres (PNs) that were synthesized by ultrasonic polymerization of pyrrole. The catalysts Pt/PCN, Pt/CN, and Pt/PN were prepared by depositing Pt nanoparticles on supports PCNs, CNs, and PNs, respectively, using ethylene glycol chemical reduction. Nitrogen adsorption, X-ray diffraction, thermogravimetric analysis, transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy were employed to characterize samples. It was found that after chemical activation using KOH, PCNs containing N functional groups (mainly N-6 and N-Q) possessed a microporous structure with a high surface area of 1010 m2/g and a particle size of less than 100 nm. The electrochemical properties of samples Pt/PCN, Pt/CN, and Pt/PN, together with commercial catalysts E-TEK (40 wt % Pt loading), were comparatively investigated in methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) for fuel cells. The results showed that the catalytic activity of Pt/PN toward both reactions at room temperature is almost negligible possibly due to the poor conductivity of support PNs proven by impedance spectroscopy, in contrast with some literature reports. Compared to Pt/CN and E-TEK catalyst, Pt/PCN revealed an enhanced mass activity in ORR and MOR because of the high dispersion of small Pt nanoparticles, the presence of nitrogen species, and developed microporous structure of support PCNs.

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