We synthesized a copper rubeanate metal organic framework (CR-MOF) which has the potential to improve the catalytic activity of electrochemical reduction of CO 2 due to its characteristics of electronic conductivity, proton conductivity, dispersed reaction sites, and nanopores. Synthesized CR-MOF particles were dropped on carbon paper (CP) to form a working electrode. The onset potential for CO 2 reduction of a CR-MOF electrode was about 0.2 V more positive than that observed on a Cu metal electrode in an aqueous electrolyte solution. Our analysis of the reduction products during potentiostatic electrolysis showed formic acid (HCOOH) to be virtually the only CO 2 reduction product on a CR-MOF electrode, whereas a Cu metal electrode generates a range of products. The quantity of products from the CR-MOF electrode was markedly greater (13-fold at −1.2 V vs. SHE) than that of a Cu metal electrode. Its stability was also confirmed. The electrochemical reduction of carbon dioxide (CO 2 ) into useful products at ambient pressures and temperatures has been a focus of research interest. A huge number of studies have been carried out in the past several decades especially for metal electrodes in aqueous media.1-4 Most metals have little catalytic activity for CO 2 reduction and mainly evolve hydrogen due to electrolysis of water, a competing reaction. Some metals produce carbon monoxide (CO) and formic acid (HCOOH), and, especially for HCOOH formation, a high applied potential of below −1.5 V vs. SHE is generally needed to obtain sufficient current for the process. Copper (Cu) has the unique property of producing hydrocarbons 3,5,6 and would appear to be the most hopeful candidate as a catalyst for CO 2 electrochemical reduction; however, Cu generates a range of reaction products and the selectivity for each product tends to be low. To improve its selectivity, there have been several explorations with metal alloys. 7 The basic idea is to disperse and specify the reaction site and to change the concentration of protons that are needed for electrochemical reduction of CO 2 . These protons are adsorbed by the atoms adjacent to each Cu site, where they induce a change in local reaction conditions and alter the reduction products of CO 2 . 8 Metal Organic Frameworks (MOFs) which have backbones constructed from metals and organic ligands have also been studied intensively. MOFs are structured and porous materials with nano-scale pores, and have been tested for applications including gas storage, 9,10 gas separation, 9,10 and heterogeneous catalysis. 9,11,12 Interestingly, some MOFs, such as copper rubeanate and its derivatives, show proton conductivity 13 that results from the adsorption of a proton to a nitrogen atom in the ligand, accompanied by electron transfer from Cu(II) ions.14 Those MOFs have been applied as electrochemical catalysts in ethanol fuel cell systems and have demonstrated selective formation of acetaldehyde as an oxidant of ethanol. 15 In spite of the interest shown in this area, there have until now been n...

CO2 reduction with water and light illumination is realized using a gallium nitride (GaN) photoelectrode in which excited electrons induce CO2 conversion at the counter electrode. For the counter electrode, a copper (Cu) plate was chosen. The low affinity and wide gap of the nitride semiconductor enable us to create an electron–hole pair which has a sufficient energy for both CO2 reduction and water oxidation, in spite of the fact that a high energy for CO2 reduction is required. Within this system, the generation of formic acid (HCOOH) with 3% Faradic efficiency was confirmed by light illumination alone.

Applying combinatorial technology to electrochemical CO2 reduction offers a broad range of possibilities for optimizing the reaction conditions. In this work, the CO2 pressure, stirring speed, and reaction temperature were varied to investigate the effect on the rate of CO2 supply to copper electrode and the associated effects on reaction products, including CH4. Experiments were performed in a 0.5 M KCl solution using a combinatorial screening reactor system consisting of eight identical, automatically controlled reactors. Increasing the CO2 pressure and stirring speed, or decreasing the temperature, steadily suppressed H2 production and increased the production of other reaction products including CH4 across a broad range of current densities. Our analysis shows that the CO2 pressure, stirring speed, and reaction temperature independently contributed to the limiting rate of CO2 supply to the electrode (Jlim). At a constant temperature, the limiting current density of CH4 increased proportionally with Jlim, illustrating that the production rate of CH4 was proportional to CO2 supply. Varying the CO2 pressure and stirring speed hardly affected the maximum Faradaic efficiency of CH4 production. However, changes to the reaction temperature showed a significant contribution to CH4 selectivity. This study highlights the importance of quantitative analysis of CO2 supply in clarifying the role of various reaction parameters and understanding more comprehensively the selectivity and reaction rate of electrochemical CO2 reduction.

We report on a highly improved CO2 to HCOOH conversion system using a tandem photo-electrode (TPE) of InGaN and two Si p-n junctions. To improve its efficiency, narrow-band-gap InGaN was applied as the photo-absorption layer. In the TPE structure, the current matching between GaN-based photo-absorption layer and two Si p-n junctions is crucial for the improvement of the efficiency. The energy conversion efficiency for HCOOH production reached 0.97%, which is greater than average of global biological photosynthetic one.

In recent years, piezoelectric materials have been widely investigated for harvesting energy from ambient vibrations. A vibrating piezoelectric device (PD) generates alternating current (AC), which needs to be converted into direct current (DC) for powering electronic devices or for storage. A traditional full-wave bridge rectifier (FBR) interface circuit serves this purpose, but it suffers from high power loss due to the presence of high forward voltage across the diodes. In this paper, an improved H-Bridge rectifier circuit is proposed as the AC-DC rectifier circuit to reduce power loss for high frequency and low amplitude application. The performance of the proposed rectifier circuit was experimentally studied, analysed and discussed. Two different testing scenarios for high frequency, namely, varying input power with fixed excitation frequency and varying excitation frequency with fixed input voltage were considered. Applicability of the circuit at low frequency range was also investigated. The outcome shows that the proposed circuit notably increases the voltage and the power produced from the PD when compared to traditional FBR circuits.