The key challenges involved in cost-effective formation of solar fuels are therefore as follows:
(1) Use advances in biotechnology to genetically engineer plants to more
efficiently — by a factor of 10 — harvest solar energy into biomass, so as to
require less land area to produce the needed amount of stored biomass energy;(2) Genetically engineer photosynthetic bacterial organisms to produce solar-
derived fuels;(3) Replicate the essential components of the machinery of photosynthesis outside
of a natural organism or plant(i.e., in an artificial photosynthetic system) and
obtain the needed ten- or hundred-fold efficiency improvement in a robust,
cost-effective system;(4) Construct entirely man-made chemical components (out of either organic or
inorganic molecules or inorganic semiconductor particles) that, as an
assembly, mimic photosynthesis by absorbing sunlight and converting the
energy into chemical fuels such as CH 4 and H 2 ; the process developed must be
efficient, robust, scaleable, and cost-effective.Each of these endeavors has significant knowledge gaps that need to be bridged to provide the
basis for a viable and economically acceptable energy conversion technology. For example,
artificial photosynthetic systems constructed from the key components of photosynthesis can
effectively separate charge after absorption of light, but they cannot now be assembled robustly
with the needed membranes and catalysts to sustain fuel production. Systems that use man-made
chemical components can effectively form fuels, but they either require a consumable chemical
reagent as input to the system, or they cease to function after a short time period in the
laboratory. Systems based on semiconducting particles either become corroded in sunlight or the
systems that are stable become inefficient when irradiated with visible light and only work well
in ultraviolet (UV) light.
The challenges involve some of the most fundamental questions in chemistry, materials science,
and molecular biology: How can we direct and control the non-covalent assembly of a complex
system of molecules to achieve a desired structure and function? How can we mimic the role of a
protein matrix without reconstructing that entire protein de novo? Can we develop effective
catalysts that can take separated charges — regardless of whether they are produced from solar
electric photovoltaic (PV) cells or from molecule-based, light-absorbing assemblies — and
convert those electrical charges into chemical fuels efficiently and without excessive energy
losses during the process? These fundamental research efforts, targeted toward effective and
robust solar energy conversion systems, form the basis for the priority research directions
(PRDs) on solar fuels that are summarized as the outcome of the workshop.
In the first part of this Panel Survey, we discuss current efforts to exploit recent breakthroughs in
molecular biology to optimize the production of biomass. Much of this new understanding
derives from the development of a detailed picture of how the molecular machinery of
photosynthesis captures and converts sunlight into chemical energy. The discovery of structural