Harvesting the full bandwidth of the solar spectrum, especially the near-infrared portion, remains a challenge for solar-to-fuel conversion technology. Plasmonic nanostructures have recently attracted attention in this connection due to their enhanced yet tunable broadband absorption and photochemical stability. Here we report a nanoplasmonic photocatalytic construct by decorating plasmonic Au nanorods with CoO for harvesting visible and NIR light via the photoelectrochemical water oxidation reaction (WOR). In contrast to previous reports of plasmonic photocatalyst constructs, our structure does not require complicated fabrication or rely on rare-earth heavyatom elements and exhibits excellent photostability without leaching of either cobalt or gold into the reaction solution under photoelectrochemical conditions. This catalytic construct triggered photoelectrochemical WOR with the generation of significant photocurrent (∼100 μA cm −2 ) while producing photogenerated oxygen at 18.1 mmol h −1 and hydrogen at 40.2 mmol h −1 (on the counter electrode) per milligram of cobalt under broadband excitation of 410−1700 nm with photon-tooxygen conversion efficiency of ∼0.05% in neutral aqueous conditions. The broadband photocatalytic activity of CoOdecorated Au nanorods was attributed to the hot holes generated by the photoexcitation of plasmonic gold nanorods.

A new fiber-optic technique to eliminate residual amplitude modulation in tunable diode laser wavelength modulation spectroscopy is presented. The modulated laser output is split to pass in parallel through the gas measurement cell and an optical fiber delay line, with the modulation frequency / delay chosen to introduce a relative phase shift of pi between them. The two signals are balanced using a variable attenuator and recombined through a fiber coupler. In the absence of gas, the direct laser intensity modulation cancels, thereby eliminating the high background. The presence of gas induces a concentration-dependent imbalance at the coupler's output from which the absolute absorption profile is directly recovered with high accuracy using 1f detection.

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