Matthew T. Mayer

Bio: Matthew T. Mayer is an academic researcher from Helmholtz-Zentrum Berlin. The author has contributed to research in topics: Water splitting & Catalysis. The author has an hindex of 32, co-authored 45 publications receiving 6526 citations. Previous affiliations of Matthew T. Mayer include Boston College & École Polytechnique Fédérale de Lausanne.

Water photolysis at 12.3% efficiency via perovskite photovoltaics and Earth-abundant catalysts

Abstract: Although sunlight-driven water splitting is a promising route to sustainable hydrogen fuel production, widespread implementation is hampered by the expense of the necessary photovoltaic and photoelectrochemical apparatus. Here, we describe a highly efficient and low-cost water-splitting cell combining a state-of-the-art solution-processed perovskite tandem solar cell and a bifunctional Earth-abundant catalyst. The catalyst electrode, a NiFe layered double hydroxide, exhibits high activity toward both the oxygen and hydrogen evolution reactions in alkaline electrolyte. The combination of the two yields a water-splitting photocurrent density of around 10 milliamperes per square centimeter, corresponding to a solar-to-hydrogen efficiency of 12.3%. Currently, the perovskite instability limits the cell lifetime.

Cu2O Nanowire Photocathodes for Efficient and Durable Solar Water Splitting

Abstract: Due to its abundance, scalability, and nontoxicity, Cu2O has attracted extensive attention toward solar energy conversion, and it is the best performing metal oxide material. Until now, the high efficiency devices are all planar in structure, and their photocurrent densities still fall well below the theoretical value of 14.5 mA cm(-2) due to the incompatible light absorption and charge carrier diffusion lengths. Nanowire structures have been considered as a rational and promising approach to solve this issue, but due to various challenges, performance improvements through the use of nanowires have rarely been achieved. In this work, we develop a new synthetic method to grow Cu2O nanowire arrays on conductive fluorine-doped tin oxide substrates with well-controlled phase and excellent electronic and photonic properties. Also, we introduce an innovative blocking layer strategy to enable high performance. Further, through material engineering by combining a conformal nanoscale p-n junction, durable protective overlayer, and uniform catalyst decoration, we have successfully fabricated Cu2O nanowire array photocathodes for hydrogen generation from solar water splitting delivering unprecedentedly high photocurrent densities of 10 mA cm(-2) and stable operation beyond 50 h, establishing a new benchmark for metal oxide based photoelectrodes.

Boosting the performance of Cu2O photocathodes for unassisted solar water splitting devices

Abstract: Although large research efforts have been devoted to photoelectrochemical (PEC) water splitting in the past several decades, the lack of efficient, stable and Earth-abundant photoelectrodes remains a bottleneck for practical application. Here, we report a photocathode with a coaxial nanowire structure implementing a Cu2O/Ga2O3-buried p–n junction that achieves efficient light harvesting across the whole visible region to over 600 nm, reaching an external quantum yield for hydrogen generation close to 80%. With a photocurrent onset over +1 V against the reversible hydrogen electrode and a photocurrent density of ~10 mA cm−2 at 0 V versus the reversible hydrogen electrode, our electrode constitutes the best oxide photocathode for catalytic generation of hydrogen from sunlight known today. Conformal coating via atomic-layer deposition of a TiO2 protection layer enables stable operation exceeding 100 h. Using NiMo as the hydrogen evolution catalyst, an all Earth-abundant Cu2O photocathode was achieved with stable operation in a weak alkaline electrolyte. To show the practical impact of this photocathode, we constructed an all-oxide unassisted solar water splitting tandem device using state-of-the-art BiVO4 as the photoanode, achieving ~3% solar-to-hydrogen conversion efficiency. The generation of hydrogen fuel from water and visible light requires photoelectrodes that are inexpensive, stable and highly active. Now, Luo, Gratzel and co-workers report Cu2O photocathodes that reach these goals. Incorporation into an unassisted solar water splitting device gives ~3% solar-to-hydrogen conversion efficiency.

Hematite-based water splitting with low turn-on voltages.

Abstract: Sunlight-driven photoelectrochemical (PEC) water splitting offers promise as a method for effective solar-energy harvesting and storage. To transform the reaction into economically competitive technology, we need materials that can absorb sunlight broadly, transfer the energy to excited charges at high efficiencies, and catalyze specific reduction and oxidation reactions. Furthermore, the materials should be inexpensive and stable against photocorrosion. To date, an ideal material that satisfies all of these considerations remains elusive. This challenge can, in principle, be addressed by combining various material components, each purposedesigned to offer desired properties with respect to photovoltage generation, charge transport, and catalytic activity. For example, it has recently been shown that the performance of hematite (a-Fe2O3)-based water splitting can indeed be improved by introducing dedicated charge collectors, buried homoand heterojunctions, and oxygen-evolution catalysts. Hematite was chosen as a prototypical system for these proof-of-concept demonstrations because it is an earth-abundant material with great promise for high-efficiency, low-cost water splitting. To realize the potential of hematite, however, we still need to address a key issue concerning its low photovoltage (Vph, typically 0.4 V), which is unreasonably low given that the bandgap of hematite is 2.0 eV. For successful integration with a small-bandgap photocathode, the photovoltage generated at the photoanode needs to be significantly higher so that a total (combined) photovoltage of 1.61 V (or greater, with a minimum overpotential of 0.38 V) is produced. Herein we show that this issue may be addressed by modifying the hematite surface. When decorated with an amorphous NiFeOx layer (Figure 1), hematite produces photovoltages as high as 0.61 V, which enable the observation of turn-on voltages (Von) as low as 0.62 V (versus the reversible hydrogen electrode, RHE) without the need for a second absorber (unless otherwise noted, all electrochemical potentials reported herein are relative to RHE). When a second absorber, Si, was added, a record-low turn-on voltage of 0.32 V was measured. The basis for our approach is illustrated schematically in Figure 2. The fundamental reason for the observed limited photovoltage generation by hematite lies in the relatively positive positions of its valenceand conduction-band edges. However, even within these limits, the Vph value of 0.6–0.8 V calculated for reported flat-band potentials (Vfb) of 0.4–0.6 V has not been reached.We understand the cause of this discrepancy to be a partial Fermi level pinning effect. That is, owing to the existence of surface states, a nonnegligible potential drop takes place within the Helmholtz layer (hH, Figure 2a). [22] The effect is manifested as a more positive Von value, since a significant portion of the applied potential is used to overcome the overpotential hH (Figure 2c). Appropriate surface modification enables the hH to be minimized or eliminated (Figure 2b) and a less positive Von value to be measured (Figure 2d). The effect of the NiFeOx overlayer was profound: it led to a Von shift from approximately 1.0 V to approximately 0.6 V (Figure 1b). Although the apparent effect of the cathodic Von shift is similar to the effect of reducing the kinetic over[*] C. Du, Dr. X. Yang, Dr. M. T. Mayer, H. Hoyt, J. Xie, Dr. G. McMahon, G. Bischoping, Prof. Dr. D. Wang Department of Chemistry Merkert Chemistry Center, Boston College 2609 Beacon Street, Chestnut Hill, MA, 20467 (USA) E-mail: dunwei.wang@bc.edu Homepage: http://www2.bc.edu/dunwei-wang [] These authors contributed equally to this work.

Solar conversion of CO2 to CO using Earth-abundant electrocatalysts prepared by atomic layer modification of CuO

Abstract: The solar-driven electrochemical reduction of CO2 to fuels and chemicals provides a promising way for closing the anthropogenic carbon cycle. However, the lack of selective and Earth-abundant catalysts able to achieve the desired transformation reactions in an aqueous matrix presents a substantial impediment as of today. Here we introduce atomic layer deposition of SnO2 on CuO nanowires as a means for changing the wide product distribution of CuO-derived CO2 reduction electrocatalysts to yield predominantly CO. The activity of this catalyst towards oxygen evolution enables us to use it both as the cathode and anode for complete CO2 electrolysis. In the resulting device, the electrodes are separated by a bipolar membrane, allowing each half-reaction to run in its optimal electrolyte environment. Using a GaInP/GaInAs/Ge photovoltaic we achieve the solar-driven splitting of CO2 into CO and oxygen with a bifunctional, sustainable and all Earth-abundant system at an efficiency of 13.4%. Electrochemical reduction of CO2 to CO is a route to synthesize fuels, but cheaper and more selective catalysts are required. Using a cell equipped with a bipolar membrane and the same Earth-abundant electrocatalyst at each electrode, Schreier et al. selectively produce CO, powered by a triple-junction photovoltaic.

Metal-free efficient photocatalyst for stable visible water splitting via a two-electron pathway

Abstract: The use of solar energy to produce molecular hydrogen and oxygen (H2 and O2) from overall water splitting is a promising means of renewable energy storage. In the past 40 years, various inorganic and organic systems have been developed as photocatalysts for water splitting driven by visible light. These photocatalysts, however, still suffer from low quantum efficiency and/or poor stability. We report the design and fabrication of a metal-free carbon nanodot-carbon nitride (C3N4) nanocomposite and demonstrate its impressive performance for photocatalytic solar water splitting. We measured quantum efficiencies of 16% for wavelength λ = 420 ± 20 nanometers, 6.29% for λ = 580 ± 15 nanometers, and 4.42% for λ = 600 ± 10 nanometers, and determined an overall solar energy conversion efficiency of 2.0%. The catalyst comprises low-cost, Earth-abundant, environmentally friendly materials and shows excellent stability.

Visible-light driven heterojunction photocatalysts for water splitting – a critical review

Abstract: Solar driven catalysis on semiconductors to produce clean chemical fuels, such as hydrogen, is widely considered as a promising route to mitigate environmental issues caused by the combustion of fossil fuels and to meet increasing worldwide demands for energy. The major limiting factors affecting the efficiency of solar fuel synthesis include; (i) light absorption, (ii) charge separation and transport and (iii) surface chemical reaction; therefore substantial efforts have been put into solving these problems. In particular, the loading of co-catalysts or secondary semiconductors that can act as either electron or hole acceptors for improved charge separation is a promising strategy, leading to the adaptation of a junction architecture. Research related to semiconductor junction photocatalysts has developed very rapidly and there are a few comprehensive reviews in which the strategy is discussed (A. Kudo and Y. Miseki, Chemical Society Reviews, 2009, 38, 253–278, K. Li, D. Martin, and J. Tang, Chinese Journal of Catalysis, 2011, 32, 879–890, R. Marschall, Advanced Functional Materials, 2014, 24, 2421–2440). This critical review seeks to give an overview of the concept of heterojunction construction and more importantly, the current state-of-the art for the efficient, visible-light driven junction water splitting photo(electro)catalysts reported over the past ten years. For water splitting, these include BiVO4, Fe2O3, Cu2O and C3N4, which have attracted increasing attention. Experimental observations of the proposed charge transfer mechanism across the semiconductor/semiconductor/metal junctions and the resultant activity enhancement are discussed. In parallel, recent successes in the theoretical modelling of semiconductor electronic structures at interfaces and how these explain the functionality of the junction structures is highlighted.

Homogeneously dispersed, multimetal oxygen-evolving catalysts

Abstract: Earth-abundant first-row (3d) transition metal-based catalysts have been developed for the oxygen-evolution reaction (OER); however, they operate at overpotentials substantially above thermodynamic requirements. Density functional theory suggested that non-3d high-valency metals such as tungsten can modulate 3d metal oxides, providing near-optimal adsorption energies for OER intermediates. We developed a room-temperature synthesis to produce gelled oxyhydroxides materials with an atomically homogeneous metal distribution. These gelled FeCoW oxyhydroxides exhibit the lowest overpotential (191 millivolts) reported at 10 milliamperes per square centimeter in alkaline electrolyte. The catalyst shows no evidence of degradation after more than 500 hours of operation. X-ray absorption and computational studies reveal a synergistic interplay between tungsten, iron, and cobalt in producing a favorable local coordination environment and electronic structure that enhance the energetics for OER.

Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology.

Abstract: Organometal halide perovskites are inexpensive materials with desirable characteristics of color-tunable and narrow-band emissions for lighting and display technology, but they suffer from low photoluminescence quantum yields at low excitation fluencies. Here we developed a ligand-assisted reprecipitation strategy to fabricate brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots with absolute quantum yield up to 70% at room temperature and low excitation fluencies. To illustrate the photoluminescence enhancements in these quantum dots, we conducted comprehensive composition and surface characterizations and determined the time- and temperature-dependent photoluminescence spectra. Comparisons between small-sized CH3NH3PbBr3 quantum dots (average diameter 3.3 nm) and corresponding micrometer-sized bulk particles (2–8 μm) suggest that the intense increased photoluminescence quantum yield originates from the increase of exciton binding energy due to size reduction as well a...

Efficient perovskite solar cells via improved carrier management

Abstract: Metal halide perovskite solar cells (PSCs) are an emerging photovoltaic technology with the potential to disrupt the mature silicon solar cell market. Great improvements in device performance over the past few years, thanks to the development of fabrication protocols1-3, chemical compositions4,5 and phase stabilization methods6-10, have made PSCs one of the most efficient and low-cost solution-processable photovoltaic technologies. However, the light-harvesting performance of these devices is still limited by excessive charge carrier recombination. Despite much effort, the performance of the best-performing PSCs is capped by relatively low fill factors and high open-circuit voltage deficits (the radiative open-circuit voltage limit minus the high open-circuit voltage)11. Improvements in charge carrier management, which is closely tied to the fill factor and the open-circuit voltage, thus provide a path towards increasing the device performance of PSCs, and reaching their theoretical efficiency limit12. Here we report a holistic approach to improving the performance of PSCs through enhanced charge carrier management. First, we develop an electron transport layer with an ideal film coverage, thickness and composition by tuning the chemical bath deposition of tin dioxide (SnO2). Second, we decouple the passivation strategy between the bulk and the interface, leading to improved properties, while minimizing the bandgap penalty. In forward bias, our devices exhibit an electroluminescence external quantum efficiency of up to 17.2 per cent and an electroluminescence energy conversion efficiency of up to 21.6 per cent. As solar cells, they achieve a certified power conversion efficiency of 25.2 per cent, corresponding to 80.5 per cent of the thermodynamic limit of its bandgap.