Pt-free tandem molecular photoelectrochemical cells for water splitting driven by visible light

Abstract

Photoelectrochemical (PEC) cells using molecular catalysts to split water into hydrogen and oxygen have been investigated intensively during the past years. However, the high-cost of Pt counter electrodes and instability of molecular PEC cells hinder the practical applications. We describe in this article a Pt-free tandem molecular PEC cell, for the first time, employing molecular ruthenium- and cobalt-catalysts with strong dipicolinic acid anchoring groups on the respective photoanode and photocathode for total water splitting. The Pt-free tandem molecular PEC cell showed an effective and steady photocurrent density of ca. 25 μA cm(-2) for water splitting driven by visible light without external bias. This study indicates that tandem molecular PEC cells can provide great potential to the Pt-free devices for light driven total water splitting.

Molecular Catalyst Immobilized Photocathodes for Water/Proton and Carbon Dioxide Reduction

“…[41] To improvet he stability of the catalysto nt he NiO surface, Sun and co-workersi ntroduced pyridine-2,6-dicarboxylic acid (PDA)a sastrong and stable anchoring group in both aH 2 evolution catalyst (CoHEC)a nd an O 2 evolution catalyst (RuOEC) (see Figure 4). [41] To improvet he stability of the catalysto nt he NiO surface, Sun and co-workersi ntroduced pyridine-2,6-dicarboxylic acid (PDA)a sastrong and stable anchoring group in both aH 2 evolution catalyst (CoHEC)a nd an O 2 evolution catalyst (RuOEC) (see Figure 4).…”

“…Reproduced and modified from Ref [41]. b) Energy levels and electron/hole-transferp rocesses occurring in the tandem molecularP EC cell.…”

CdSe quantum dots/molecular cobalt catalyst co-grafted open porous NiO film as a photocathode for visible light driven H2 evolution from neutral water

“…[13][14][15][16][17][18][19][20] In the pioneer work, it was found that the organic dye-sensitized NiO photocathodes with or without HER catalyst displayed low photocurrent and poor stability in the HER. 13,14 Chemically bonding both a ruthenium polypyridylchromophore and a cobaloxime catalyst to the NiO film, either with a cascade or 3 a parallel linkage, provided more stable NiO-based photocathode, which displayed the photocurrents of about 13−20 μA cm −2 at an applied potential of −0.2 V vs. NHE (the potentials mentioned hereafter are versus NHE if not specially denoted) for the HER.…”

“…13,14 Chemically bonding both a ruthenium polypyridylchromophore and a cobaloxime catalyst to the NiO film, either with a cascade or 3 a parallel linkage, provided more stable NiO-based photocathode, which displayed the photocurrents of about 13−20 μA cm −2 at an applied potential of −0.2 V vs. NHE (the potentials mentioned hereafter are versus NHE if not specially denoted) for the HER. 15,16 The reason for the low activities of these sensitized NiO photocathodes may stem from several factors: (i) the small hole diffusion coefficient in NiO, 21,22 (ii) the competition of the hole injection from a sensitizer to the valence band of NiO with the fast recombination between the reduced dye and the holes generated in NiO, and (iii) poor sensitizer loading dominantly due to the low specific surface area of NiO. Some recent studies showed that compared to dye-sensitized NiO photocathodes, the quantum dot (QD)-sensitized NiO cathodes exhibited much larger hole diffusion coefficient.…”

A solution-processed, mercaptoacetic acid-engineered CdSe quantum dot photocathode for efficient hydrogen production under visible light irradiation

“…To avoid the use of any sacrificial agent and generate H 2 in an environmentally friendly manner, photoelectrochemical (PEC) 40 production of H 2 is an ideally clean and renewable mean that integrates solar energy collection and water reduction into a single photoelectrode. [24][25][26][27][28][29] In fact, the recent interest in utilizing QDs for harvesting light energy offers new ways to control light conversion efficiency in the solar cells. [30][31][32][33] However, PEC 45 studies involving QDs-sensitized photoelectrodes have focused almost exclusively on photoanodes, where photocurrents result from light-simulated electron transfer from QDs into the conduction bands of an n-type semiconductor, such as TiO 2 .…”