Prolonged hydrogen production by engineered green algae photovoltaic power stations.

Interest in securing energy production channels from renewable sources is higher than ever due to the daily observation of the impacts of climate change. A key renewable energy harvesting strategy achieving carbon neutral cycles is artificial photosynthesis. Solar-to-fuel routes thus far relied on elaborately crafted semiconductors, undermining the cost-efficiency of the system. Furthermore, fuels produced required separation prior to utilization. As an artificial photosynthesis design, here we demonstrate the conversion of swimming green algae into photovoltaic power stations. The engineered algae exhibit bioelectrogenesis, en route to energy storage in hydrogen. Notably, fuel formation requires no additives or external bias other than CO2 and sunlight. The cellular power stations autoregulate the oxygen level during artificial photosynthesis, granting immediate utility of the photosynthetic hydrogen without separation. The fuel production scales linearly with the reactor volume, which is a necessary trait for contributing to the large-scale renewable energy portfolio.

Quadruple nanoelectrode assembly for simultaneous analysis of multiple redox species and its application to multi-channel scanning electrochemical microscopy.

Development of ultramicroelectrodes and nanoelectrodes opened interesting possibilities in the investigation electron transfer phenomena, including their application as probe electrodes in scanning electrochemical microscopy (SECM). Analytical prowess of SECM was often shadowed by long operation times required for analysis of a wide sample area. In this report, we developed a multi-channel nanoelectrode bundle for simultaneous electroanalysis of multiple orthogonal redox reactions in one bath. Four nanoelectrodes of diameters 100-400 nm were shown to be bundled in a 2 µm disk area. The nanoelectrode assembly was implemented as a tip electrode for multi-channel SECM, dramatically improving the time efficiency of SECM operations. The nanoelectrode bundle was also demonstrated as a stand-alone microprobe for electroanalytical investigations in small volumes such as ceramic confinements and biologically important compartments. The development reported in this work should benefit electrochemical analyses of various systems, especially those involving SECM and fine spatial control.

A novel class of oxynitrides stabilized by nitrogen dimer formation.

Despite the wide applicability of oxynitrides from photocatalysis to refractory coatings, our understanding of the materials has been limited in terms of their thermodynamics. The configurational entropy via randomly mixed O/N or via cation vacancies are known to stabilize oxynitrides, despite the positive formation enthalpies. Here, using tin oxynitrides as a model system, we show by ab initio computations that oxynitrides in seemingly charge-unbalanced composition stabilize by forming pernitrides among metal-(O,N)6 octahedra. The nitrogen pernitride dimer, =(N-N)=, results in the effective charge of -4, facilitating the formation of nitrogen-rich oxynitrides. We report that the dimer forms only in structures with corner-sharing octahedra, since the N-N bond formation requires sufficient rotational degrees of freedom among the octahedra. X-ray photoemission spectra of the synthesized tin oxynitride films reveal two distinct nitrogen bonding environments, confirming the computation results. This work opens the search space for a novel kind of oxynitrides stabilized by N dimer formation, with specific structural selection rules.

Nonvolatile resistance switching on two-dimensional electron gas.

Two-dimensional electron gas (2DEG) at the complex oxide interfaces have brought about considerable interest for the application of the next-generation multifunctional oxide electronics due to the exotic properties that do not exist in the bulk. In this study, we report the integration of 2DEG into the nonvolatile resistance switching cell as a bottom electrode, where the metal-insulator transition of 2DEG by an external field serves to significantly reduce the OFF-state leakage current while enhancing the on/off ratio. Using the Pt/Ta2O5-y/Ta2O5-x/SrTiO3 heterostructure as a model system, we demonstrate the nonvolatile resistance switching memory cell with a large on/off ratio (>10(6)) and a low leakage current at the OFF state (∼10(-13) A). Beyond exploring nonvolatile memory, our work also provides an excellent framework for exploring the fundamental understanding of novel physics in which electronic and ionic processes are coupled in the complex heterostructures.

Sensitivity enhancement of nanostructured SnO2 gas sensors fabricated using the glancing angle deposition method.

0.5 wt.% Pd-catalyzed SnO2 thin-film gas sensors with microstructures controlled on a nanometer scale were fabricated by an e-beam evaporator using the glancing angle deposition (GAD) method. After annealing at 500 degrees C for 1 h, the sensors produced were polycrystalline with a nanoporous, tilted columnar microstructure. The gas-sensing properties of these SnO2 sensors were measured in the concentration range of 1 to 5 ppm NO2 at 250 degrees C and of 10 to 50 ppm C2H5OH at 400 degrees C, respectively. The sensors fabricated by e-beam evaporation in combination with the GAD method showed much higher sensitivities than normally prepared sensors and exhibited rapid response times. The gas sensitivity (S = R(gas)/R(air)) of the SnO2 sensor using the GAD method was 43.4 for 5 ppm NO2 and 0.08 for 10 ppm C2H5OH, respectively. These sensors showed excellent sensitivities compared to the normal thin film sensors (S = 2 for 5 ppm NO2 and 0.92 for 10 ppm C2H5OH). We consider that the nanostructured sensors produced using the GAD process could be used to detect various gases emitted by automobiles and industrial installations.