Heterojunction PEC with MIEC Oxide for High-Temp Water Splitting
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Solution Overview
Problem
Current photoelectrochemical cells (PECs) face challenges in efficiently converting solar energy into chemical energy due to limitations in material combinations that absorb the visible solar spectrum, minimize overpotential losses, achieve proper energetic alignment, and exhibit stability, particularly at elevated temperatures, leading to restricted operating ranges and reduced solar-to-hydrogen efficiency.
Innovation Solution
A solid-state PECs based on a heterojunction between a semiconductor light absorber and a mixed ionic and electronic conducting (MIEC) oxide, which captures both thermal and photon energy from concentrated sunlight, allowing operation at elevated temperatures (673-973 K) and reducing system complexity by using a solid ionic conductor instead of liquid or polymer electrolytes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional PECs operate at room temperature with liquid or polymer electrolytes, then the system is simple to operate, but the operating temperature range is restricted and solar-to-hydrogen efficiency is reduced
Solution Approach 1:
The patent changes the physical state parameter of the electrolyte from liquid/polymer to solid oxide, enabling operation at elevated temperatures (673-973 K) while maintaining system stability. This parameter change resolves the contradiction by expanding the operating temperature range without proportionally increasing device complexity
Solution Approach 2:
The patent employs composite material structures including heterojunctions between semiconductor light absorbers and metal oxide catalysts, combined with solid oxide electrolytes. This composite approach enables high-temperature operation while managing the complexity through integrated material design
2Use of energy by moving object
If heterojunctions are used to harvest solar spectrum, then solar energy absorption is improved, but carrier recombination rate increases due to uphill barriers at the interface
Solution Approach 1:
The patent applies local quality optimization by carefully engineering the band alignment at the heterojunction interface between semiconductor light absorbers and metal oxide catalysts. By creating proper energetic alignment locally at the interface, the patent reduces uphill barriers and minimizes carrier recombination while maintaining effective solar spectrum harvesting
Solution Approach 2:
The patent introduces metal oxide catalysts as intermediary materials between the semiconductor light absorber and the electrolyte. These intermediaries facilitate carrier transport across the heterojunction interface, reducing recombination losses while enabling effective solar energy utilization
3Productivity
If overpotential is increased to drive reaction at rate matching solar flux, then reaction rate is improved, but energy loss increases significantly
Solution Approach 1:
The patent changes the operating temperature parameter to elevated ranges (673-973 K), which thermally activates the electrochemical reactions. This parameter change reduces the overpotential required to achieve reaction rates matching solar flux, thereby reducing energy losses while maintaining high productivity
Solution Approach 2:
The patent introduces thermal energy as an additional dimension to drive the electrochemical reactions, complementing the photon-driven processes. By operating at elevated temperatures, the system utilizes thermal activation to reduce kinetic barriers, decreasing overpotential requirements while maintaining high reaction rates
Data Source
AI summary
A solid-state PEC includes mixed ionic and electronic conducting oxides that allow it to operate at temperatures significantly above ambient utilizing both the light and thermal energy available from concentrated sunlight to dissociate water vapor. The solid-state PEC has a semiconductor light absorber coated with a thin MIEC oxide for improved catalytic activity, electrochemical stability and ionic conduction, which is located between the gas phase and the semiconductor light absorber. As a result, the MIEC oxide provides a facile path for minority carriers to reach the water vapor as well as a path for the ionic carriers to reach the solid electrolyte. Elevated temperature operation allows reasonable band misalignments at the interfaces to be overcome, reduces the required overpotential, and facilitates rapid product diffusion away from the surface.