A self-driving laboratory advances the Pareto front for material properties.

Useful materials must satisfy multiple objectives, where the optimization of one objective is often at the expense of another. The Pareto front reports the optimal trade-offs between these conflicting objectives. Here we use a self-driving laboratory, Ada, to define the Pareto front of conductivities and processing temperatures for palladium films formed by combustion synthesis. Ada discovers new synthesis conditions that yield metallic films at lower processing temperatures (below 200 °C) relative to the prior art for this technique (250 °C). This temperature difference makes possible the coating of different commodity plastic materials (e.g., Nafion, polyethersulfone). These combustion synthesis conditions enable us to to spray coat uniform palladium films with moderate conductivity (1.1 × 105 S m-1) at 191 °C. Spray coating at 226 °C yields films with conductivities (2.0 × 106 S m-1) comparable to those of sputtered films (2.0 to 5.8 × 106 S m-1). This work shows how a self-driving laboratoy can discover materials that provide optimal trade-offs between conflicting objectives.

Photoelectrochemical Decomposition of Lignin Model Compound on a BiVO4 Photoanode.

The photoelectrochemical decomposition of lignin model compounds at a BiVO4 photoanode is demonstrated with simulated sunlight and an applied bias of 2.0 V. These prototypical lignin model compounds are photoelectrochemically converted into the corresponding aryl aldehyde and phenol derivatives in a single step with conversion of up to ≈64 % over 20 h. Control experiments suggest that vanadium sites are electrocatalytically active, which precludes the need for a redox mediator in solution. This feature of the system is corroborated by a layer of V2 O5 deposited on BiVO4 serving to boost the conversion by 10 %. Our methodology capitalizes on the reactive power of sunlight to drive reactions that have only been studied previously by electrochemical or catalytic methods. The use of a BiVO4 photoanode to drive lignin model decomposition therefore provides a new platform to extract valuable aromatic chemical feedstocks using solar energy, electricity and biomass as the only inputs.

Stabilizing Copper for CO2 Reduction in Low-Grade Electrolyte.

We demonstrate herein a CO2 reduction electrocatalyst regeneration strategy based on the manipulation of the Cu(0)/Cu2+ equilibrium with high concentrations of ethylenediaminetetraacetic acid (EDTA). This strategy enables the sustained performance of copper catalysts in distilled and tap water electrolytes for over 12 h. The deposition of common electrolyte impurities such as iron, nickel, and zinc is blocked because EDTA can effectively bind the metal ions and negatively shift the electrode potential of M/M n+. The Cu/Cu2+ redox couple is >600 mV more positive than the other metal ions and therefore participates in an equilibrium of dissolution and redeposition from and to the electrode in high concentrations of EDTA. These dynamic equilibria serve to further regenerate the surface copper catalyst to prevent the deactivation of catalytic sites. On the basis of this strategy, we show that >95% of initial hydrocarbon production activity can be maintained for 12 h in KHCO3 (99% purity) enriched distilled water and 6 h in KHCO3 (99% purity) enriched tap water.

Brass and Bronze as Effective CO2 Reduction Electrocatalysts.

Electrochemically reducing CO2 into fuels using renewable electricity is a contemporary global challenge that requires significant advances in catalyst design. Photodeposition techniques were used to screen ternary alloys of Cu-Zn-Sn, which includes brass and bronze, for the electrocatalytic reduction of CO2 to CO and formate. This analysis identified Cu0.2 Zn0.4 Sn0.4 and Cu0.2 Sn0.8 to be capable of reaching Faradaic efficiencies of >80 % for CO and formate formation, respectively, and capable of achieving partial current densities of 3 mA cm-2 at an overpotential of merely 200 mV.

Photodecomposition of Metal Nitrate and Chloride Compounds Yields Amorphous Metal Oxide Films.

UV light is found to trigger the decomposition of MClx or M(NO3)x (where M = Fe, Co, Ni, Cu, or Zn) to form uniform, amorphous films of metal oxides. This process does not elevate the temperature of the substrate and thus conformal films can be coated on a range of substrates, including rigid glass and flexible plastic. The formation of the oxide films were confirmed by a combination of powder X-ray diffraction, X-ray photoelectron spectroscopy, X-ray fluorescence spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy techniques. Amorphous oxide films of iron, nickel and a combination of iron and nickel demonstrated oxygen evolution reaction electrocatalytic activities commensurate with films of the same compositions prepared by widely used electrodeposition and sputtering methods. These results illuminate a potential route to amorphous oxides at scale using simple metal precursors without vacuum or heat.

Photoelectrochemical oxidation of organic substrates in organic media.

There is a global effort to convert sunlight into fuels by photoelectrochemically splitting water to form hydrogen fuels, but the dioxygen byproduct bears little economic value. This raises the important question of whether higher value commodities can be produced instead of dioxygen. We report here photoelectrochemistry at a BiVO4 photoanode involving the oxidation of substrates in organic media. The use of MeCN instead of water enables a broader set of chemical transformations to be performed (e.g., alcohol oxidation and C-H activation/oxidation), while suppressing photocorrosion of BiVO4 that otherwise occurs readily in water, and sunlight reduces the electrical energy required to drive organic transformations by 60%. These collective results demonstrate the utility of using photoelectrochemical cells to mediate organic transformations that otherwise require expensive and toxic reagents or catalysts.Photoelectrochemical water splitting is a promising method for H2 fuel production, but the O2 by-product generated has little economic value. Here, Berlinguette and colleagues demonstrate that BiVO4 photoanodes immersed in organic media can instead perform valuable alcohol oxidation and C-H functionalization reactions.

High-Throughput Synthesis of Mixed-Metal Electrocatalysts for CO2 Reduction.

The utilization of CO2 as a feedstock requires fundamental breakthroughs in catalyst design. The efficiencies and activities of pure metal electrodes towards the CO2 reduction reaction are established, but the corresponding data on mixed-metal systems are not as well developed. In this study we show that the near-infrared driven decomposition (NIRDD) of solution-deposited films of metal salts and subsequent electrochemical reduction offers the unique opportunity to form an array of mixed-metal electrocatalyst coatings with excellent control of the metal stoichiometries. This synthetic method enabled us to develop an empirical structure-property correlation to help inform the development of optimized CO2 catalyst compositions.

Near-infrared-driven decomposition of metal precursors yields amorphous electrocatalytic films.

Amorphous metal-based films lacking long-range atomic order have found utility in applications ranging from electronics applications to heterogeneous catalysis. Notwithstanding, there is a limited set of fabrication methods available for making amorphous films, particularly in the absence of a conducting substrate. We introduce herein a scalable preparative method for accessing oxidized and reduced phases of amorphous films that involves the efficient decomposition of molecular precursors, including simple metal salts, by exposure to near-infrared (NIR) radiation. The NIR-driven decomposition process provides sufficient localized heating to trigger the liberation of the ligand from solution-deposited precursors on substrates, but insufficient thermal energy to form crystalline phases. This method provides access to state-of-the-art electrocatalyst films, as demonstrated herein for the electrolysis of water, and extends the scope of usable substrates to include nonconducting and temperature-sensitive platforms.