Abstract
The production of hydrogen by water splitting has been a very attractive idea for several decades. However, the energy consumption that is necessary for water oxidation is too high for practical applications. On the contrary, the oxidation of organics is a much easier and less energy-demanding process. In addition, it may be used to consume organic wastes with a double environmental benefit: renewable energy production with environmental remediation. The oxidation of organics in a photoelectrochemical cell, which in that case is also referenced as a photocatalytic fuel cell, has the additional advantage of providing an alternative route for solar energy conversion. With this in mind, the present work describes a realistic choice of materials for the Pt-free photoelectrochemical production of hydrogen, by employing ethanol as a model organic fuel. The photoanode was made of a combination of titania with cadmium sulfide as the photosensitizer in order to enhance visible light absorbance. The cathode electrode was a simple carbon paper. Thus, it is shown that substantial hydrogen can be produced without electrocatalysts by simply exploiting carbon electrodes. Even though an ion transfer membrane was used in order to allow for an oxygen-free cathode environment, the electrolyte was the same in both the anode and cathode compartments. An alkaline electrolyte has been used to allow high hydroxyl concentration, thus facilitating organic fuel (photocatalytic) oxidation. Hydrogen production was then obtained by water reduction at the cathode (counter) electrode.
Highlights
Hydrogen production by water splitting has been one of the most attractive research subjects for several decades
The nanoparticulate titania film deposited on the photoanode electrode was, as already said, approximately 10-μm thick and presented a mesoporous structure, as typical of films made of P25 nanoparticles
We have shown that hydrogen can be photoelectrochemically produced by using a simple carbon paper as counter electrode
Summary
Hydrogen production by water splitting has been one of the most attractive research subjects for several decades. Water splitting is a rather high energy-demanding process. Water is electrochemically split (oxidized) at +1.23 V, but in reality, much higher voltages are necessary due to losses [1]. In this respect, expensive catalysts are necessary to limit the applied electric potential [2]. A better situation presents itself when in the place of water, an organic agent is electrochemically oxidized, since the oxidation of some organic materials is achieved at lower potentials [3,4]. Seen from a different point of view, the most crucial issue is related to the oxidation of water being a four-electron process: 2H2 O→O2 +4H+ +4e−
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