3 research outputs found
Electrochemical Stability of Metastable Materials
We
present a first-principles-based formalism to provide a quantitative
measure of the thermodynamic instability and propensity for electrochemical
stabilization, passivation, or corrosion of metastable materials in
aqueous media. We demonstrate that this formalism can assess the relative
Gibbs free energy of candidate materials in aqueous media as well
as their decomposition products, combining solid and aqueous phases,
as a function of pH and potential. On the basis of benchmarking against
20 stable as well as metastable materials reported in the literature
and also our experimental characterization of metastable triclinic-FeVO<sub>4</sub>, we present quantitative estimates for the relative Gibbs
free energy and corresponding aqueous regimes where these materials
are most likely to be stable, form inert passivating films, or steadily
corrode to aqueous species. Furthermore, we show that the structure
and composition of the passivating films formed on triclinic-FeVO<sub>4</sub> are also in excellent agreement with the Point Defect Model,
as proposed by the corrosion community. An open-source web application
based on the formalism is made available at https://materialsproject.org
Discovery of Manganese-Based Solar Fuel Photoanodes via Integration of Electronic Structure Calculations, Pourbaix Stability Modeling, and High-Throughput Experiments
The solar photoelectrochemical
generation of hydrogen and carbon-containing
fuels comprises a critical energy technology for establishing sustainable
energy resources. The photoanode, which is responsible for solar-driven
oxygen evolution, has persistently limited technology advancement
due to the lack of materials that exhibit both the requisite electronic
properties and operational stability. Efforts to extend the lifetime
of solar fuel devices increasingly focus on mitigating corrosion in
the highly oxidizing oxygen evolution environment, motivating our
development of a photoanode discovery pipeline that combines electronic
structure calculations, Pourbaix stability screening, and high-throughput
experiments. By applying the pipeline to ternary metal oxides containing
manganese, we identify a promising class of corrosion-resistant materials
and discover five oxygen evolution photoanodes, including the first
demonstration of photoelectrocatalysis with Mn-based ternary oxides
and the introduction of alkaline earth manganates as promising photoanodes
for establishing a durable solar fuels technology
Discovery and Characterization of a Pourbaix-Stable, 1.8 eV Direct Gap Bismuth Manganate Photoanode
Solar-driven oxygen
evolution is a critical technology for renewably
synthesizing hydrogen- and carbon-containing fuels in solar fuel generators.
New photoanode materials are needed to meet efficiency and stability
requirements, motivating materials explorations for semiconductors
with (i) band-gap energy in the visible spectrum and (ii) stable operation
in aqueous electrolyte at the electrochemical potential needed to
evolve oxygen from water. Motivated by the oxygen evolution competency
of many Mn-based oxides, the existence of several Bi-containing ternary
oxide photoanode materials, and the variety of known oxide materials
combining these elements with Sm, we explore the Bi–Mn–Sm
oxide system for new photoanodes. Through the use of a ferri/ferrocyanide
redox couple in high-throughput screening, BiMn<sub>2</sub>O<sub>5</sub> and its alloy with Sm are identified as photoanode materials with
a near-ideal optical band gap of 1.8 eV. Using density functional
theory-based calculations of the mullite Bi<sup>3+</sup>Mn<sup>3+</sup>Mn<sup>4+</sup>O<sub>5</sub> phase, we identify electronic analogues
to the well-known BiVO<sub>4</sub> photoanode and demonstrate excellent
Pourbaix stability above the oxygen evolution Nernstian potential
from pH 4.5 to 15. Our suite of experimental and computational characterization
indicates that BiMn<sub>2</sub>O<sub>5</sub> is a complex oxide with
the necessary optical and chemical properties to be an efficient,
stable solar fuel photoanode