Direct Electrocatalytic Methanol Oxidation on MoO3/Ni(OH)2: Exploiting Synergetic Effect of Adjacent Mo and Ni.

Ni-based materials have been widely investigated as methanol oxidation reaction (MOR) catalysts. The formation of NiOOH and its reduction to Ni(OH)2 are generally regarded as essential steps for methanol oxidation. However, in such an indirect route, the efficiency of proton coupled electron transfer is fundamentally limited by the rate of transition from Ni(OH)2 to NiOOH back and forth. Herein we demonstrate a direct MOR pathway on MoO3/Ni(OH)2 without the formation of a NiOOH mediator. The MoO3/Ni(OH)2 exhibits a benchmark electrocatalytic MOR current density of 1000 mA cm-2 at 1.52 V vs. RHE with a nearly 100% faradic efficiency, outperforming all the state of art MOR electrocatalysts. In-situ Raman spectroscopy confirms that NiOOH is not formed during the electrocatalytic MOR process on the MoO3/Ni(OH)2. Density functional theory calculations suggest that Ni2+ in MoO3/Ni(OH)2 serves as the methanol adsorption site while the doped Mo6+ plays a key role in capturing the deprotonated H·. Benefiting from the Mo-Ni synergistic effect, the energy barrier of the CH2O* → CHO* + H* process is significantly reduced, avoiding the NiOOH formation and leading to the direct MOR. Our research unravels a direct electrochemical MOR pathway that does not rely on NiOOH formation and provides a facile strategy of regulating the intermediate process barrier for MOR.

Ultrathin CuBi2O4 on a bipolar Bi2O3 nano-scaffold: a self-powered broadband photoelectrochemical photodetector with improved responsivity and response speed.

CuBi2O4 is a promising photoactive material for photoelectrochemical (PEC) broadband photodetectors due to its suitable band structure, but its photo-responsivity is severely limited by the short carrier diffusion length and long light penetration depth. To address the trade-off between light absorption and charge separation, a nano-structured bipolar Bi2O3 host scaffold was coupled with an ultrathin CuBi2O4 light absorbing layer to construct a host-guest Bi2O3/CuBi2O4 photocathode. The work function of the bipolar Bi2O3 scaffold lies in between FTO and CuBi2O4, making Bi2O3 a suitable back contact layer for hole transport. Compared with the flat CuBi2O4 and Bi2O3 scaffold counterpart, the nanostructured Bi2O3/CuBi2O4 exhibits significantly improved light absorption and enhanced charge separation efficiency. The Bi2O3/CuBi2O4 PEC photodetector can be self-powered and demonstrates a broad photo-response ranging from ultraviolet (UV) to near infrared (NIR). It shows a high responsivity of 75 mA W-1 and a remarkable short response time of 0.18 ms/0.19 ms. Bi2O3/CuBi2O4 prepared by magnetron sputtering demonstrates great potential for rapid PEC photodetection in a wide optical domain.

Size-Independent Reconfigurable Logic Gate with Bismuth Oxide Based Photoelectrochemical Device.

XOR gate, an important building block in computational circuits, is often constructed by combining other basic logic gates, and the hybridity inevitably leads to its complexity. A photoelectrochemical device could realize XOR function based on the current change of the photoelectrode; however, such signal is highly sensitive to photoelectrode size and therefore requires precise manufacturing at a high cost. Herein we developed a novel XOR gate based on the light-induced open-circuit potential (OCP) of the Bi2O3 photoelectrode. Surprisingly, the OCP of Bi2O3 does not increase with light intensity according to the traditional logarithmic relationship. Instead, an unusual decrease in OCP is observed at high light intensity, which is attributed to the dramatic light-induced increase in surface states that can be easily regulated by varying the oxygen partial pressure during reactive magnetron sputtering. Based on such a nonmonotonic variation of OCP, a facile Bi2O3-based gate is designed to realize the XOR function. Unlike the commonly used current signal, OCP is size independent, and therefore, the Bi2O3-based gate does not require high manufacturing accuracy. Moreover, in addition to XOR, the Bi2O3-based PEC gate also demonstrates great versatility in realizing other logic functions including AND, OR, NOT, NIH, NAND, and NOR. The strategy of modulating and applying nonmonotonic OCP signal opens a new avenue for designing size-independent reconfigurable logic gates at low manufacturing cost.

Self-passivated CuV2O6 as a universal photoelectrode material for reliable and accurate photoelectrochemical sensing.

Photoelectrochemical (PEC) detection has attracted intensive attention during the past decade. Currently, most research focuses on improving the sensitivity and selectivity of the PEC sensor, but the issue of the stability of the photoelectrode material under the testing environment is often ignored or lacks in-depth investigation. Herein, we develop a novel CuV2O6 photoelectrode exhibiting superior stability under the testing environment through self-passivation. CuV2O6-based PEC sensors are fabricated for the first time for highly selective carcinoembryonic antigen (CEA) and human serum alpha fetoprotein (AFP) detection. The CuV2O6 shows great potential as a universal photoelectrode material for reliable and accurate PEC detection of macromolecules.