Pathways to electrochemical solar hydrogen technologies

Solar powered electrochemical production of hydrogen through water electrolysis is an active and important research endeavor. However, technologies and roadmaps for implementation of this process do not exist. In this perspective paper, we describe potential pathways for solar hydrogen technologies into the marketplace in the form of photoelectrochemical or photovoltaic driven electrolysis devices and systems. We detail technical approaches for device and system architectures, economic drivers, societal perceptions, political impacts, technological challenges, and research opportunities. Implementation scenarios are broken down into short term and long term markets, and a specific technology roadmap is defined. In the short term, the only plausible economical option will be photovoltaic driven electrolysis systems for niche applications. In the long term, electrochemical solar hydrogen technologies could be deployed more broadly in energy markets but will require advances in the technology, significant cost reductions, and or policy changes. Ultimately, a transition to a society that significantly relies on solarhydrogen technologies will benefit from continued creativity and influence from the scientific communit

Pathways to Electrochemical Solar-Hydrogen Technologies

Solar-powered electrochemical production of hydrogen through water electrolysis is an active and important research endeavor. However, technologies and roadmaps for implementation of this process do not exist. In this perspective paper, we describe potential pathways for solar-hydrogen technologies into the marketplace in the form of photoelectrochemical or photovoltaic-driven electrolysis devices and systems. We detail technical approaches for device and system architectures, economic drivers, societal perceptions, political impacts, technological challenges, and research opportunities. Implementation scenarios are broken down into short-term and long-term markets, and a specific technology roadmap is defined. In the short term, the only plausible economical option will be photovoltaic-driven electrolysis systems for niche applications. In the long term, electrochemical solar-hydrogen technologies could be deployed more broadly in energy markets but will require advances in the technology, significant cost reductions, and/or policy changes. Ultimately, a transition to a society that significantly relies on solar-hydrogen technologies will benefit from continued creativity and influence from the scientific community.Solid state NMR/Biophysical Organic Chemistr

Tandem Cu2O-covered silicon micropillar photocathodes for solar-to-fuel devices

At present, nearly 75% of the world’s energy consumption is supplied from fossil fuels such as coal, petroleum, and natural gas. A major part of this is utilized by the transportation sector and the remainder is used for electricity generation in power stations that burn fossil fuels. The combustion of fossil fuels to harvest their stored carbon-based energy is a primary source of greenhouse gas emissions, mainly in the form of carbon dioxide (CO2) and consequently is responsible for global warming. For these reasons, interest in and harvesting of solar energy as a crucial alternative clean energy source have developed quickly in current years. As a main source of energy, solar energy has the potential to deliver all energy desired by mankind. Solar technology implementation has been broadly focused on electricity generation. Despite recent progress in solar electrical energy generation, important issues remain unsolved, such as the continued need for high-power energy demand for transport, central heating, and industrial processes, and the intermittency problem, such as caused by the alternation of summer and winter periods. One of the proposed solutions is to construct a solar-to-fuel (S2F) device, which describes the concept of turning solar energy into storable fuel. To fabricate a fully integrated, efficient S2F device based on photo-electricity, a single or set of semiconductors must be combined with a proper electrocatalyst. In this thesis, we show various geometries and materials combinations for a S2F device, primarily based on copper-based photocatalyst with structured silicon as a base material, employing device structuring and modification

Efficient Solar Water Splitting Photocathodes Comprising a Copper Oxide Heterostructure Protected by a Thin Carbon Layer

Photoelectrochemical (PEC) solar water splitting has received extensive attention because it promises to provide an alternative and sustainable source of energy. A key challenge is to achieve a stable PEC system in either acidic or basic electrolyte without degradation of the (photo)electrodes. We have used a cubic Cu2O film and porous granular bilayer Cu2O/CuO composite with a carbon protection layer as photocathode materials. The films were deposited under different conditions, such as variation of the electrodeposition time, thermal oxidation of the Cu2O films in air versus nitrogen atmosphere, and deposition of the carbon materials, and were investigated structurally and with regard to their PEC performance. The optimized electrodes showed photocurrents up to 6.5 and 7.5 mA/cm-2 at potentials of 0 and -0.1 V vs RHE at pH 5.5, respectively. The stabilities of the Cu2O/C and Cu2O/CuO/C photocathodes, at a low bias of 0.3 V vs RHE, were retained after 50 h. The strongly improved photostability of the photocathodes in comparison to electrodes in the absence of a carbon overlayer is attributed to a more effective charge transfer and a protective role of carbon against photocorrosion

Tandem Cuprous Oxide/Silicon Microwire Hydrogen-Evolving Photocathode with Photovoltage Exceeding 1.3 V

Large research efforts have been devoted to optimizing the output of earth-abundant photoabsorbers in solar-to-fuel (S2F) devices. Here, we report a Cu2O/Ga2O3 heterojunction/Si microwire photocathode with an underlying buried radial Si p–n junction, which achieves efficient light harvesting across the visible spectrum to over 600 nm, reaching an external quantum yield for hydrogen generation close to 80%, with a photocurrent onset above +1.35 V vs RHE, a photocurrent density of ∼10 mA/cm2 at 0 V vs RHE, and an ideal regenerative efficiency of 5.51%. We show step-by-step the effects of every photocathode design element (i.e., Si p–n junction, Cu2O layer thickness, microwire length, microwire pitch, etc.) on the overall efficiency of our final microwire Si/Cu2O photocathode by comparing every addition to a baseline Cu2O photocathode. Lastly, we show a stable operation exceeding 200 h at a bias potential of +1.0 V vs RHE, with an average current density of 4.5 mA/cm2

Improving Charge Separation in Cu2O/g-C3N4/CoS Photocathodes by a Z-Scheme Heterojunction to Achieve Enhanced Performance and Photostability

Fabricating efficient heterojunction photocathodes to accelerate charge transport and long-term stability is important to promote visible light-driven hydrogen evolution. With the strategic combination of type II band edge heterojunctions and passivation layers of graphitic carbon nitride (g-C3N4), Cu2O/g-C3N4/CoS photocathodes that achieve high photostability have been fabricated. We used spin-coating and electrospinning techniques to synthesize g-C3N4nanosheets and nanowires, respectively, which were deposited on Cu2O on fluorine-doped tin oxide (FTO) substrates. In case of Cu2O/g-C3N4nanosheets, the loading of g-C3N4was varied from 1 to 7 wt% and the highest photocatalytic activity (5.8 mA/cm2at 0 V RHE) was obtained for the heterojunction prepared from the 5 wt% solution. For g-C3N4nanowires, varying the electrospinning time (from 0.5 to 12 min) controlled the loading of these nanowires, and the heterojunction with 8 min spinning time displayed the highest photocurrent density (6.6 mA/ cm2at 0 V vs RHE). The higher photocatalytic activity and better stability of the Cu2O/g-C3N4nanowires (8 min)/CoS heterojunction arises from the effective separation and transport of photo-generated charge carriers, which was confirmed by photoluminescence and photocurrent measurements, and from proper protection of the underlying Cu2O photocathode. Importantly, the Cu2O/g-C3N4heterojunction decorated by CoS proved to be effective for enhancing the stabilization of the Cu2O photocathode. About 90-95% of the photocurrent density was retained after 5 h of illumination and the faradaic efficiency for hydrogen evolution reached 80%. These results and protocols contribute to the progress of Cu2O-based photocathodes to be applied in high-efficiency solar hydrogen devices with prolonged photostability

Tandem Cuprous Oxide/Silicon Microwire Hydrogen-Evolving Photocathode with Photovoltage Exceeding 1.3 v

Large research efforts have been devoted to optimizing the output of earth-abundant photoabsorbers in solar-to-fuel (S2F) devices. Here, we report a Cu2O/Ga2O3 heterojunction/Si microwire photocathode with an underlying buried radial Si p-n junction, which achieves efficient light harvesting across the visible spectrum to over 600 nm, reaching an external quantum yield for hydrogen generation close to 80%, with a photocurrent onset above +1.35 V vs RHE, a photocurrent density of ∼10 mA/cm2 at 0 V vs RHE, and an ideal regenerative efficiency of 5.51%. We show step-by-step the effects of every photocathode design element (i.e., Si p-n junction, Cu2O layer thickness, microwire length, microwire pitch, etc.) on the overall efficiency of our final microwire Si/Cu2O photocathode by comparing every addition to a baseline Cu2O photocathode. Lastly, we show a stable operation exceeding 200 h at a bias potential of +1.0 V vs RHE, with an average current density of 4.5 mA/cm