The selectivity of H 2 , CO, CH 4 and C 2 H 4 produced during the electrolysis of CO 2 in aqueous solution at copper electrodes has been investigated in relation to surface analysis of the electrodes after electrolysis by XPS and temperature-programmed photoelectron emission (TPPE) and surface potential (SP) measurements. The electrodes were prepared as follows: (A) only ultrasonic cleaning in acetone; (B) oxidation in air; (C) exposure to argon plasma. The electrolysis time was 3 h at a given potential. With electrode A, on increasing the potential in a negative direction the amount of CH 4 increased, accompanied by a decrease in the amounts of H 2 and CO, and the SP value was positive and shifted in a more positive direction, the TPPE activity increased and in the O1s XPS spectra a peak assigned to adsorbed oxygen developed. The amount of C 2 H 4 was greater in the potential range where both metallic Cu and Cu 2 O existed. With electrode B, the main product was H 2 , the SP value was negative, the TPPE activity was much smaller and Cu 2 O existed more preferentially than metallic Cu. With electrode C, the surface underwent oxidation easily when immersed in solution. With increasing plasma treatment time the hydrocarbon products decreased, the SP value was lower and the TPPE activity was smaller. It is suggested that the adsorbed oxygen present at the electrode surfaces can lead to an increase in the number of electrons available at the surfaces and also contribute to the adsorption of CO 2 , resulting in hydrocarbon production.

Electrochemical reduction of CO2 at copper electrodes and its relationship to the metal surface characteristics

"The origins of triboemission -- Correlating wear damage with electron emission"

The influence of temperature and surface overlayer on the photoelectron emission from scratched real iron surfaces was investigated using thermally assisted photoelectron emission (TAPE) and X-ray photoelectron spectroscopy (XPS) measurements. The scratching was conducted with a diamond cutter in seven atmospheres. The intensity of TAPE as a function of temperature, called glow curve, was measured in the range 25–339 °C using a Geiger counter under ultraviolet irradiation at 210 nm. The temperature was scanned in two cycles (Up1 and Down1, and Up2 and Down2). The XPS measurements were carried out at 25 °C and after TAPE measurements at 200 and 339 °C. The photoelectron emission intensity at 40 °C in the Up1 scan increased in the order of air < water ≈ methanol ≈ cyclohexane < ethanol < benzene < acetone, and then each glow curve exhibited a gradual increase with temperature through a broad peak. It was found that the dependence of the emission intensity in the Up1 scan on the oxygen component ratio, ZO = O2−/(OH− + O2−) and the percentage of the Fe metal and FeOOH components of the Fe3p spectra for the atmospheres greatly differed. Additionally, the glow curve in the Up1 scan was completely different from that in the other scans. It was proposed that the photoelectron emission in the Up1 scan originates from not only the base metal but also the surface overlayer having trapped electrons and is strongly influenced by the acid–base interaction of the surface hydroxyl groups with the liquids molecules. Copyright © 2016 John Wiley & Sons, Ltd.

Photoelectron emission and XPS studies of real iron surfaces subjected to scratching in air, water, and organic liquids

To characterize easily the state of real metal surfaces in ambient environments, we have developed an extremely sensitive technique for surface analysis using photoelectron emission phenomena as a function of temperature. We will call this method temperature-programmed photoelectron emission (TPPE). The emitted electrons are detected by a gas-flow Geiger counter with Q gas. The TPPE measurement is performed by scanning the wavelength of incident UV light at different temperatures in the temperature-increase and subsequent temperature-decrease process between 25 and 350°C. A photoelectron emission (PE) spectrum representing the curve of PE intensity vs wavelength is obtained at each temperature. The number of emitted electrons in a PE spectrum is termed PE total count. The PE total count as a function of the measurement temperature was investigated for 17 kinds of commercial rolled metal sheets. The metals were distinctly classified into two main groups A and B, the former indicating a temperature-dependent PE total count and the latter a virtually temperature-independent PE total count. Group A included Al, Pt, Pb, Cu, Ag, Au and Ni; group B included Ta, Ti, Mo, Pd, W, Fe, Co, Zn, Nb and Sn. With group A, the greater amount of adsorbed oxygen present at the initial surface was found by XPS to change to the oxide oxygen after TPPE measurement. This chemical change is suggested to play a substantial role in the temperature dependence of the PE total count.

Temperature-programmed photoelectron emission technique for metal surface analysis

This chapter discusses the nature of solid surfaces, contact among solids and its effects on wear and friction. Real surfaces are composed of surface features ranging in size from individual atoms to visible grooves and ridges. Most surface features affect wear and friction. Since almost all surfaces are rough, in terms of solid contact they cannot be approximated by a flat plane. The basic laws of friction are a result of the control of solid contact by rough surfaces. The topography of the contacting surfaces therefore has a decisive effect on wear and friction. Rough surfaces have very small areas of real contact with the opposing surface and this causes wear and friction to be determined by high contact stresses and extreme concentrations of frictional energy even though the nominal contact stress and total frictional energy can be small. Friction has traditionally been divided into static and kinetic friction. Exact measurements of microscopic sliding movements reveal that as the friction force acting on a contact is progressively increased, microscopic sliding movement occurs at all levels of friction force and the maximum friction force occurs at a specific sliding speed.

Fundamentals of Contact Between Solids

The characteristics of tribostimulated electron emission (called TriboEE) have been studied for real metal surfaces subjected to rubbing with polytetrafluoroethylene (PTFE). A gas-flow Geiger counter with a counter gas called Q gas was used for observing the TriboEE. Metal samples used were as follows: Ti, Zr (group 4 in the periodic table); V, Nb, Ta (group 5); Mo, W (group 6); Fe (group 8); Co (group 9); Ni, Pd, Pt (group 10); Cu, Ag, Au (group 11); Zn (group 12); Al (group 13); and Sn (group 14). For metals in the same groups of 4, 5, 6, 10, and 11 the number of electrons ejected during rubbing time (called TriboEE total count) increased with an increase in the period for the metal. For the metals in the groups of 4, 10, and 11 the surface fluorine content originating from PTFE debris attached at the surfaces increased with an increase in the period for the metal. The TriboEE total count was almost independent of the photoelectric thresholds determined in photoemission (PE) experiment throughout the metals, while the amount of ejected electrons in the PE measurement tended to decrease with increasing threshold. The surface potential (SP) was almost unchanged before and after the TriboEE measurement. Based on the relation to XPS, PE, and SP results the TriboEE was explained as being associated with the release of electrons transported to the attached PTFE debris from the metal substrate by a surface electric field.

Observation of Real Metal Surfaces by Tribostimulated Electron Emission and Its Relationship to the Analyses by XPS and Photoemission

To easily characterize the state of real metal surfaces in ambient environments, we have developed an extremely sensitive technique for the surface analysis using photoelectron emission phenomena depending on temperature. We call this method temperature programmed photoelectron emission (TPPE). The emitted electrons were detected by a gas-flow Geiger counter with Q gas. A PE spectrum representing the curve of the PE intensity vs. wavelength was obtained at different temperatures in the temperature-increase and subsequent temperature-decrease process between 25 and 350°C. The number of emitted electrons in a PE spectrum (PE total count) as a function of the measurement temperature was investigated for 17 kinds of rolled metal sheets that were cleaned in acetone. The metals were distinctly classified into five groups A-I (Al, Pt, Pb), A-II (Ag, Cu, Au, Ni), B-III (Ta), B-IV (Pd, W, Ti, Mo), and B-V (Nb, Fe, Zn, Co, Sn). The A groups indicated a temperature dependent PE total count, while the B groups indicated a virtually temperature independent PE total count. With the A groups a greater amount of the adsorbed oxygen that was present on the initial surface was found by XPS to change to oxide oxygen after TPPE measurement, with the exception of Al. This chemical change is suggested to play a substantial role in the temperature dependence of the PE total count. With the B groups oxide oxygen existed predominantly on the initial surface, resulting in little change in the chemical state of the oxygen. It is suggested that the ability of the metals in gas chemisorption is closely related to the TPPE behavior.

Observation of Real Metal Surfaces by Temperature Programmed Photoelectron Emission Technique

The characteristics of photoelectron emission (PE) from copper abraded in organic liquids such as alcohols, aromatics, ether, ketone, and ester have been investigated. PE was measured by varying the wavelength of incident light at several temperatures between 25 and 300°C, which were successively changed in two round cycles of elevating and lowering temperatures. PE intensity depended greatly on the measurement temperature. The maximum PE appearing at 250°C in the temperature-elevation of the first cycle, also, depended markedly on the organic liquids used. The order of the maximum PE value for organic liquids was explained as corresponding significantly with that of the acid base interaction of the organic liquid and abraded surface.

Masakazu Honma

Papers

Temperature-programmed photoelectron emission technique for metal surface analysis

Observation of Real Metal Surfaces by Tribostimulated Electron Emission and Its Relationship to the Analyses by XPS and Photoemission

Observation of Real Metal Surfaces by Temperature Programmed Photoelectron Emission Technique

Photoelectron Emission from Copper Freshly Abraded in Organic Liquids