The impact of the carbon structure, the aging protocol, and the gas atmosphere on the degradation of Pt/C electrocatalysts were studied by electrochemical and spectroscopic methods. Pt nanocrystallites loaded onto high-surface area carbon (HSAC), Vulcan XC72, or reinforced-graphite (RG) with identical Pt weight fraction (40 wt %) were submitted to two accelerated stress test (AST) protocols from the Fuel Cell Commercialization Conference of Japan (FCCJ) mimicking load-cycling or start-up/shutdown events in a proton-exchange membrane fuel cell (PEMFC). The load-cycling protocol essentially caused dissolution/redeposition and migration/aggregation/coalescence of the Pt nanocrystallites but led to similar electrochemically active surface area (ECSA) losses for the three Pt/C electrocatalysts. This suggests that the nature of the carbon support plays a minor role in the potential range 0.60 < E < 1.0 V versus RHE. In contrast, the carbon support was strongly corroded under the start-up/shutdown protocol (1.0 < E < 1.5 V versus RHE), resulting in pronounced detachment of the Pt nanocrystallites and massive ECSA losses. Raman spectroscopy and differential electrochemical mass spectrometry were used to shed light on the underlying corrosion mechanisms of structurally ordered and disordered carbon supports in this potential region. Although for Pt/HSAC the start-up/shutdown protocol resulted into preferential oxidation of the more disorganized domains of the carbon support, new structural defects were generated at quasi-graphitic crystallites for Pt/RG. Pt/Vulcan represented an intermediate case. Finally, we show that oxygen affects the surface chemistry of the carbon supports but negligibly influences the ECSA losses for both aging protocols.

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The carbon dioxide reduction reaction (CO2RR) catalyzed by N‐doped carbon materials was studied under operando conditions by on line differential electrochemical mass spectrometry and in‐line gas chromatography. Fe/NC electrocatalysts were synthesized by using a Fe+2‐impregnated pyridyl/triazine complex heat treated at 800 °C in nitrogen (Fe/NC(N2)) or ammonia (Fe/NC(NH3)) atmospheres; an iron‐free nitrogen‐doped carbon electrocatalyst (NC(NH3)) was also synthesized and included for comparison. Here, superior CO faradaic efficiencies were evidenced for NC(NH3) compared to Fe/NC(NH3), independently of the applied electrode potential; however, much larger overall catalytic activity for the promotion of the CO2RR and/or HER has been observed for Fe/NC(NH3), generating different stoichiometric ratios of syngas (CO/H2). Another important evidence is that N‐pyridinic groups, even in absence of Fe−N4 moieties and presence of high iron nanoparticles loading, play an important role as active sites for selective CO2 reduction to CO at low overpotentials.

NAD-dependent alcohol dehydrogenase (ADH) enzymes for ethanol oxidation were investigated by differential electrochemical mass spectrometry (DEMS). The broad mass spectra obtained under bioelectrochemical control and with unprecedented accuracy were used to provide new insight into the enzyme kinetics and mechanisms.

The carbon oxidation reaction (COR) is a critical issue in proton‐exchange membrane fuel cells (PEMFCs), as carbon in various forms is the most used electrocatalyst support material. The COR is thermodynamically possible above the C/CO2 standard potential, but its rate becomes significantly important only at high overpotential (e. g. PEMFC cathode potential). Herein, using on‐line differential electrochemical mass spectrometry, we show that oxygen‐containing carbon surface groups present on high‐surface aera carbon, Vulcan XC72 or reinforced graphite are oxidized at PEMFC anode‐relevant potential (E=0.1 V vs. the reversible hydrogen electrode, RHE), but not at E=0.4 V vs. RHE. We rationalized our findings by considering a Pt‐catalysed decarboxylation mechanism in which Pt nanoparticles provide adsorbed hydrogen species to the oxygen‐containing carbon surface groups, eventually leading to evolution of carbon dioxide and carbon monoxide. These results shed fundamental light on an unexpected degradation mechanism and facilitate the understanding of the long‐term stability of PEMFC anode nanocatalysts.

Prussian blue (PB) and Prussian blue analogues (PBAs) are commonly synthesized by conventional methods, such as chemical precipitation, thermal decomposition, and electrochemical deposition. Herein, we have successfully synthesized Prussian blue by oxidative print light synthesis (PLS) with a cubic Fe 4 [Fe(CN) 6 ] 3 phase, as confirmed by XRD compared to pure Prussian blue. Furthermore, UV−vis, FT-IR, Raman, and XPS measurements also present experimental evidence of PB formation from the Potassium hexacyanoferrate(II) trihydrate precursor by PLS. STEM images display aggregated PB particles of ca. 500 nm with a homogeneous distribution of Fe, N, C, and K throughout the sample. The electrochemical characterization provides excellent electrocatalytic performances during the charge and discharge processes, with oxidation/reduction reactions of high-and low-spin iron, which is already known as the interconversion of Prussian white to Prussian blue (PW ⇄ PB) and Prussian blue to Prussian green (PB ⇄ PG), respectively. In particular, PLS has been successfully employed as a smart and low-cost protocol to synthesize thin Prussian blue films, and possibly other PBAs, for applications in energy storage devices such as K, Na, and Mg ion batteries.

One of the most important current topics in the renewable and sustainable energy scenario is the CO2 electro‐reduction reaction (CO2RR), which is an alternative and important route for its conversion into various high value‐added chemicals, therefore making up a CO2 recycling process. Despite its importance and the works already developed in this field, many challenges still need to be overcome for CO2RR to reach high values of efficiency and selectivity. This is even more challenging considering that this reaction occurs with the transfer of several electrons, making the investigation and elucidation of the reaction mechanism a real need. Thus, several characterization techniques have been employed, and specially, the on‐line Electrochemical Mass Spectrometry (EC‐MS) technique emerges as a powerful tool, thus making possible to improve the understanding of reaction pathways, through the identification of products and intermediaries, and allowing the screening of electrocatalyst potentials for CO2RR. Herein, we present the evolution of adaptations of general electrochemical cell designs for the study of the CO2RR.

The carbon dioxide electrocatalytic reduction is central for the development of regenerative cycles of electrochemical energy conversion and storage. Herein, the gaseous products of the CO 2 electroreduction were monitored by using an electrochemical cell on line coupled to a differential electrochemical mass spectrometer (DEMS), aiming at searching for electrocatalysts with high selectivity for CO formation. The results showed that, among the studied materials, the Cu 4 Sn/C alloy nanoparticles were stable during potentiostatic polarizations as revealed by in situ X-ray absorption spectroscopy (XAS), and the on line DEMS measurements showed the production of CO, suppression of methane and ethylene formations, and diminishing of the hydrogen evolution reaction, in relation to that on pure Cu 2 O-Cu/C. The faradaic efficiencies for CO formation were 13 and 23% for Cu 4 Sn/C and Au/C (a known electrocatalyst for CO), respectively, determined by experiments of in line gas chromatography (GC). The selectivity of Cu 4 Sn/C for CO formation was ascribed to the role of Sn atoms on stabilizing adsorbed HCOO intermediates, and hindering further hydrogenation, letting CO free for desorption. These results are expected to be used as a guide for further development of electrocatalysts with a fine-tuning of composition for increasing the faradaic efficiency of CO 2 electroreduction to CO.Keywords: CO 2 electrochemical reduction, on line DEMS, in line GC, CO formation, Cu 4 Sn/C alloy IntroductionConcomitantly with the growth of the world population, the energy demand is increasing. To satisfy this scenario, fossil fuels, such as oil, coal and natural gas, are being exhaustively used. Unfortunately, together to the dependence on these fuels, large amounts of carbon dioxide (CO 2 ) are emitted into the environment and, so, this is not a sustainable cycle. This has initiated research projects to investigate efficient processes for using the available CO 2 in the atmosphere. The electrochemical reduction of carbon dioxide is, in principle, an efficient manner that can be explored. In this context, the electroreduction of CO 2 to fuels with high-energy density or to industrial chemicals, that can be further processed to produce useful fuels, such as CO, using photovoltaic panels, with the consecutive utilization as fuel in fuel cells, would define a sustainable or regenerative cycle. [1][2][3][4][5][6][7] In the case of performing the CO 2 electroreduction to CO in parallel with the water electroreduction (or the hydrogen evolution reaction (HER)), the mixture CO + H 2 (syngas) is produced. 8,9 In the chemical industry, CO/H 2 mixtures are reacted to form methanol or other liquid fuels, such as diesel, by using the Fischer-Tropsch process. 10 The CO 2 electrochemical reduction can be productselective by using different electrocatalysts. However, even for two-electron products, it is decisive to know the kinetically important steps of the studied reaction. Also, synthesizing an optimized electrocatalyst that do not catalyze undesi...