The development of
efficient and stable earth-abundant water oxidation
catalysts is vital for economically feasible water-splitting systems.
Cobalt phosphate (CoPi)-based catalysts belong to the relevant class
of nonprecious electrocatalysts studied for the oxygen evolution reaction
(OER). In this work, an in-depth investigation of the electrochemical
activation of CoPi-based electrocatalysts by cyclic voltammetry (CV)
is presented. Atomic layer deposition (ALD) is adopted because it
enables the synthesis of CoPi films with cobalt-to-phosphorous ratios
between 1.4 and 1.9. It is shown that the pristine chemical composition
of the CoPi film strongly influences its OER activity in the early
stages of the activation process as well as after prolonged exposure
to the electrolyte. The best performing CoPi catalyst, displaying
a current density of 3.9 mA cm
–2
at 1.8 V versus
reversible hydrogen electrode and a Tafel slope of 155 mV/dec at pH
8.0, is selected for an in-depth study of the evolution of its electrochemical
properties, chemical composition, and electrochemical active surface
area (ECSA) during the activation process. Upon the increase of the
number of CV cycles, the OER performance increases, in parallel with
the development of a noncatalytic wave in the CV scan, which points
out to the reversible oxidation of Co
2+
species to Co
3+
species. X-ray photoelectron spectroscopy and Rutherford
backscattering measurements indicate that phosphorous progressively
leaches out the CoPi film bulk upon prolonged exposure to the electrolyte.
In parallel, the ECSA of the films increases by up to a factor of
40, depending on the initial stoichiometry. The ECSA of the activated
CoPi films shows a universal linear correlation with the OER activity
for the whole range of CoPi chemical composition. It can be concluded
that the adoption of ALD in CoPi-based electrocatalysis enables, next
to the well-established control over film growth and properties, to
disclose the mechanisms behind the CoPi electrocatalyst activation.
Around 50% of the world’s population, particularly in developing countries, uses biomass as one of the most common fuels. Biomass combustion releases a considerable amount of various incomplete combustion products, including particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs). The paper presents the results of Indoor Air Quality (IAQ) measurements in six houses equipped with wood burning stoves or fireplaces as heating systems. The houses were monitored for 48-h periods in order to collect PM10 samples and measure PAH concentrations. The average, the maximum and the lowest values of the 12-h PM10 concentration were 68.6 μg/m3, 350.7 μg/m3 and 16.8 μg/m3 respectively. The average benzo[a]pyrene 12-h concentration was 9.4 ng/m3, while the maximum and the minimum values were 24.0 ng/m3 and 1.5 ng/m3, respectively. Continuous monitoring of PM10, PAHs, Ultra Fine Particle (UFP) and Total Volatile Organic Compounds (TVOC) was performed in order to study the progress of pollution phenomena due to biomass burning, their trends and contributions to IAQ. The results show a great heterogeneity of impacts on IAQ in terms of magnitude and behavior of the considered pollutants’ concentrations. This variability is determined by not only different combustion technologies or biomass quality, but overall by different ignition mode, feeding and flame management, which can also be different for the same house. Moreover, room dimensions and ventilation were significant factors for pollution dispersion. The increase of PM10, UFP and PAH concentrations, during lighting, was always detected and relevant. Continuous monitoring allowed singling out contributions of other domestic sources of considered pollutants such as cooking and cigarettes. Cooking contribution produced an impact on IAQ in same cases higher than that of the biomass heating system.
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