In
spite of the enormous promise that polymeric carbon nitride (PCN) materials
hold for photoelectrochemical (PEC) applications, the fabrication of high-quality
PCN photoelectrodes has been a largely elusive goal to date. Here we tackle
this challenge by devising, for the first time, a sol–gel approach that enables
facile preparation of photoanodes based on poly(heptazine imide) (PHI), a
polymer belonging to the PCN family. The sol–gel process capitalizes on the use
of a water-soluble PHI precursor composed of nanosized (~10 nm) particles that allows
formation of a non-covalent hydrogel. The hydrogel can be deposited on a
conductive substrate resulting in formation of mechanically stable porous
polymeric thin layers (~400 nm), in contrast to the
commonly obtained loosely attached thick particulate coatings. The resulting
photoanodes exhibit unprecedented PEC performance in methanol reforming in
neutral pH electrolytes with photocurrents of up to 177±27 mA cm<sup>-2</sup> (1 sun illumination) and
320±40 mA cm<sup>-2</sup> (2 sun illumination)
at 1.23 V vs. RHE, maintaining such high photocurrents even down to ~0 V vs. RHE. These
parameters permit effective operation even without any external electric bias,
as demonstrated by bias-free photoreforming of methanol and glycerol, and highly
selective (~100%)
photooxidation of 4-methoxybenzyl alcohol (4-MBA). The robust binder-free films
derived from sol–gel processing of water-soluble PCN thus represent a new
paradigm for high-performance ‘soft-matter’ photoelectrocatalytic systems, and
pave the way for further applications in which high-quality PCN films are required.
Elucidation of the Crystal Growth Characteristics of SnO2 Nanoaggregates Formed by Sequential Low-Temperature Sol-Gel Reaction and Freeze Drying