Advances and Recent Trends in Heterogeneous Photo(Electro)-Catalysis for Solar Fuels and Chemicals

Abstract

In the context of a future renewable energy system based on hydrogen storage as energy-dense liquid alcohols co-synthesized from recycled CO2, this article reviews advances in photocatalysis and photoelectrocatalysis that exploit solar (photonic) primary energy in relevant endergonic processes, viz., H2 generation by water splitting, bio-oxygenate photoreforming, and artificial photosynthesis (CO2 reduction). Attainment of the efficiency (>10%) mandated for viable techno-economics (USD 2.00–4.00 per kg H2) and implementation on a global scale hinges on the development of photo(electro)catalysts and co-catalysts composed of earth-abundant elements offering visible-light-driven charge separation and surface redox chemistry in high quantum yield, while retaining the chemical and photo-stability typical of titanium dioxide, a ubiquitous oxide semiconductor and performance “benchmark”. The dye-sensitized TiO2 solar cell and multi-junction Si are key “voltage-biasing” components in hybrid photovoltaic/photoelectrochemical (PV/PEC) devices that currently lead the field in performance. Prospects and limitations of visible-absorbing particulates, e.g., nanotextured crystalline α-Fe2O3, g-C3N4, and TiO2 sensitized by C/N-based dopants, multilayer composites, and plasmonic metals, are also considered. An interesting trend in water splitting is towards hydrogen peroxide as a solar fuel and value-added green reagent. Fundamental and technical hurdles impeding the advance towards pre-commercial solar fuels demonstration units are considered.

Electronic Structure and Charge Transfer in the TiO2 Rutile (110)/Graphene Composite Using Hybrid DFT Calculations

“…A popular approach from previous decades has been to combine TiO 2 with cadmium sulphide (CdS) quantum dots. 1,15 Anchoring CdS to the surface of TiO 2 has been shown to increase photocatalytic activity notably and longevity to some extent, however issues with photocorrosion in particular pose a problem for potential industrial applications. 6,14,19 More recently, studies have been focussed on carbon-nanostructure/TiO 2 composite materials, 16,17,20,21 starting with carbon nanotubes (NTs) 22 27 following their isolation in the early 1990s.…”

Turning Perspective in Photoelectrocatalytic Cells for Solar Fuels

“…[50] These natural systemsa re very fragile andk ey elements for their stability are the mechanisms present in nature for limiting activity (e.g.,ifexcessive illumination by sunlight is present) and self-reparation. Whereas studies in the design of biomimetic systems are useful for understanding, [73][74][75][76][77][78][79][80] practical implementation of PECa cells requires focusing attentiono nd ifferent aspects, discussed in more detail in the following section. Whereas studies in the design of biomimetic systems are useful for understanding, [73][74][75][76][77][78][79][80] practical implementation of PECa cells requires focusing attentiono nd ifferent aspects, discussed in more detail in the following section.…”

“…Reaching a1 0% solar-to-fuel conversion with nonprecious materials [114] is thus ah ighly valuable result,o btained in as pecific case by am odular PV-electrochemical device, but only in combination with effective low-costing production, highp roductivity,a nd stability. From this perspective, the need for large efforts to develop H 2 evolution catalysts [15,79,[115][116][117] has to be reconsidered, although this is clearly relevant in terms of understanding how the overpotential in this reactionc an be reduced. The question is simple.…”

Electro‐ and Photo‐driven Reduction of CO2 by a trans‐(Cl)‐[Os(diimine)(CO)2Cl2] Precursor Catalyst: Influence of the Diimine Substituent and Activation Mode on CO/HCOO− Selectivity

“…The use of solar energy appears to be an attractive solution to the problem and photochemical reduction of CO 2 is currently av ery activea nd intense area of research. [2] In that field, two strategies are considered,t he first one, which is the more developed, is based on the use of doped or sensitized wide band gap semi-conductors as the photocatalyst, [3] the second use ap urem olecular strategy inspired by the natural photosynthesis process. [4] However,t he number of efficient photocatalysts for CO 2 reduction remains extremely limited owing to the fact that these molecules must be capable of acting both as ar edox photosensitizer and ac atalyst.…”

“…In that sense, some coordination complexes that have the ability to act in solution as photosensitizers with long-lived charge-transfere xcited states, together with the possibility of variable redox states and vacant coordination sites for binding intermediates,a re strongly attractive for playing thatr ole. [5] The [Re(NN)(CO) 3 X] (NN = 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen)d erivatives;X = labile ligand or solvent) first developed in the eighties by J.-M. Lehn et al remains the archetype of this kind of compounds, [6] in addition to some Co II and Fe III tetraaza macrocycles [7] and, more recently developed, some Ir III complexes [5b, 8] also exhibit interesting potentialitiest oa chievet his photocatalysis. Relateds ystems based on carbonyl complexes of other metals such as [Ru(NN)(CO) 2 X 2 ] [9] or more recently [Mn(NN)(CO) 3 X] [10] have shown their ability to electrocatalyze the reduction of CO 2 but the photocatalysis can only be performed in homogeneous solution in association with ar edox photosensitizer.…”