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Microalgae and cyanobacteria are some of nature’s finest examples of solar energy conversion systems, effortlessly transforming inorganic carbon into complex molecules through photosynthesis. The efficiency of energy-dense hydrocarbon production by photosynthetic organisms is determined in part by the light collected by the microorganisms. Therefore, optical engineering has the potential to increase the productivity of algae cultivation systems used for industrial-scale biofuel synthesis. Herein, we explore and report emerging and promising material science and engineering innovations for augmenting microalgal photosynthesis. Photosynthetic microalgae could provide an ecologically sustainable route to produce solar biofuels and high-value chemicals. Here, the authors review various optical management strategies used to manipulate the incident light in order to increase the efficiency of microalgae biofuel production.

Chemicals manufacturing consumes large amounts of energy and is responsible for a substantial portion of global carbon emissions. Electrochemical systems that produce the desired compounds by using renewable electricity offer a route to lower carbon emissions in the chemicals sector. Ethylene oxide is among the world’s most abundantly produced commodity chemicals because of its importance in the plastics industry, notably for manufacturing polyesters and polyethylene terephthalates. We applied an extended heterogeneous:homogeneous interface, using chloride as a redox mediator at the anode, to facilitate the selective partial oxidation of ethylene to ethylene oxide. We achieved current densities of 1 ampere per square centimeter, Faradaic efficiencies of ~70%, and product specificities of ~97%. When run at 300 milliamperes per square centimeter for 100 hours, the system maintained a 71(±1)% Faradaic efficiency throughout.

Performing CO 2 reduction in acidic conditions enables high single-pass CO 2 conversion efficiency. However, a faster kinetics of the hydrogen evolution reaction compared to CO 2  reduction limits the selectivity toward multicarbon products. Prior studies have shown that adsorbed hydroxide on the Cu surface promotes CO 2  reduction in neutral and alkaline conditions. We posited that limited adsorbed hydroxide species in acidic CO 2 reduction could contribute to a low selectivity to multicarbon products. Here we report an electrodeposited Cu catalyst that suppresses hydrogen formation and promotes selective CO 2 reduction in acidic conditions. Using in situ time-resolved Raman spectroscopy, we show that a high concentration of CO and OH on the catalyst surface promotes C-C coupling, a finding that we correlate with evidence of increased CO residence time. The optimized electrodeposited Cu catalyst achieves a 60% faradaic efficiency for ethylene and 90% for multicarbon products. When deployed in a slim flow cell, the catalyst attains a 20% energy efficiency to ethylene, and 30% to multicarbon products. Performing CO 2 reduction in acidic conditions enables high CO 2 utilization. Here, the authors report an electrodeposited Cu catalyst which achieves a 60% faradaic efficiency for ethylene and 90% for multicarbon products–both records for acidic CO 2 reduction.

A rapid energy transition will require new heat transfer fluids, and a faster means of discovering and optimizing them. Existing methods, however, are constrained by speed, accuracy, and sample volume — with accurate measurements requiring large sample volumes and long equilibration times. Here, we present a measurement approach that bypasses precise temperature measurement and heat flux measurements. Thermal conductivity, k , is determined by comparing thermally driven voltage variations across an array of resistive heaters embedded in fluid cavities. This measurement, relative to the reference material, minimizes errors from ambient temperature fluctuation, unquantified heat losses, and measurement uncertainties, and it eliminates direct temperature sensing. We report a microfluidic device and measurement method that implements in-run on-chip auto-calibration with a reference material; we test the device on a wide range of substances, including liquids, gases, mixtures, and nanofluids. It delivers results in <10 s, using ~5 µL of sample, about two orders of magnitude faster than conventional steady-state methods — while maintaining accuracy competitive with gold-standard techniques (mean signed error 0.0030 ± 0.0059 W/(m · K) (1.4% ± 3.1%), median absolute error 0.0019 W/(m · K) (MAPE 2.6 %), and expanded uncertainty of k , U  = 8.3% ± 0.24% (SD across 10 runs)). This approach makes thermal conductivity measurement accessible to accelerated materials discovery and optimization workflows. The discovery of efficient heat transfer fluids is limited by slow, manual-intensive measurement methods. Here, the authors design a microfluidic device that rapidly and accurately measures thermal conductivity using identical resistive heaters in symmetric microchannels, requiring only ~5 μL of sample in under 10 seconds.

Electrochemical reduction of CO 2 to multi-carbon products (C 2+ ), when powered using renewable electricity, offers a route to valuable chemicals and fuels. In conventional neutral-media CO 2 -to-C 2+ devices, as much as 70% of input CO 2 crosses the cell and mixes with oxygen produced at the anode. Recovering CO 2 from this stream adds a significant energy penalty. Here we demonstrate that using a liquid-to-liquid anodic process enables the recovery of crossed-over CO 2 via facile gas-liquid separation without additional energy input: the anode tail gas is directly fed into the cathodic input, along with fresh CO 2 feedstock. We report a system exhibiting a low full-cell voltage of 1.9 V and total carbon efficiency of 48%, enabling 262 GJ/ton ethylene, a 46% reduction in energy intensity compared to state-of-art single-stage CO 2 -to-C 2+ devices. The strategy is compatible with today’s highest-efficiency electrolyzers and CO 2 catalysts that function optimally in neutral and alkaline electrolytes. In the electrified conversion of CO2 to multicarbon products, CO2 crossover to the O2-rich anodic stream adds a further, energy-intensive, chemical separation step. Here, the authors demonstrate a strategy that eliminates the separation requirement.

Electrochemical reduction of CO 2 (CO 2 R) to formic acid upgrades waste CO 2 ; however, up to now, chemical and structural changes to the electrocatalyst have often led to the deterioration of performance over time. Here, we find that alloying p-block elements with differing electronegativities modulates the redox potential of active sites and stabilizes them throughout extended CO 2 R operation. Active Sn-Bi/SnO 2 surfaces formed in situ on homogeneously alloyed Bi 0.1 Sn crystals stabilize the CO 2 R-to-formate pathway over 2400 h (100 days) of continuous operation at a current density of 100 mA cm −2 . This performance is accompanied by a Faradaic efficiency of 95% and an overpotential of ~ −0.65 V. Operating experimental studies as well as computational investigations show that the stabilized active sites offer near-optimal binding energy to the key formate intermediate *OCHO. Using a cation-exchange membrane electrode assembly device, we demonstrate the stable production of concentrated HCOO – solution (3.4 molar, 15 wt%) over 100 h. Stable electrochemical reduction to formate is still challenging. Here, the authors demonstrate a redox-modulation and active-site stabilization strategy for CO 2 to formate conversion over 100 days of continuous operation at 100 mA/cm 2 with a cathodic energy efficiency of 70%.

The electrochemical reduction of CO2 to multi-carbon products has attracted much attention because it provides an avenue to the synthesis of value-added carbon-based fuels and feedstocks using renewable electricity. Unfortunately, the efficiency of CO2 conversion to C2 products remains below that necessary for its implementation at scale. Modifying the local electronic structure of copper with positive valence sites has been predicted to boost conversion to C2 products. Here, we use boron to tune the ratio of Cuδ+ to Cu0 active sites and improve both stability and C2-product generation. Simulations show that the ability to tune the average oxidation state of copper enables control over CO adsorption and dimerization, and makes it possible to implement a preference for the electrosynthesis of C2 products. We report experimentally a C2 Faradaic efficiency of 79 ± 2% on boron-doped copper catalysts and further show that boron doping leads to catalysts that are stable for in excess of ~40 hours while electrochemically reducing CO2 to multi-carbon hydrocarbons.

The copper (Cu)-catalyzed electrochemical CO 2 reduction provides a route for the synthesis of multicarbon (C 2+ ) products. However, the thermodynamically favorable Cu surface (i.e. Cu(111)) energetically favors single-carbon production, leading to low energy efficiency and low production rates for C 2+ products. Here we introduce in situ copper faceting from electrochemical reduction to enable preferential exposure of Cu(100) facets. During the precatalyst evolution, a phosphate ligand slows the reduction of Cu and assists the generation and co-adsorption of CO and hydroxide ions, steering the surface reconstruction to Cu (100). The resulting Cu catalyst enables current densities of > 500 mA cm −2 and Faradaic efficiencies of >83% towards C 2+ products from both CO 2 reduction and CO reduction. When run at 500 mA cm −2 for 150 hours, the catalyst maintains a 37% full-cell energy efficiency and a 95% single-pass carbon efficiency throughout. Copper electrocatalysts enable carbon dioxide/carbon monoxide reduction but suffer from low production rates. Here, the authors promote in situ growth of Cu(100) during electrolysis, enabling efficient and stable electrosynthesis of multicarbon products at industrially-relevant current densities

In alkaline and neutral MEA CO 2 electrolyzers, CO 2 rapidly converts to (bi)carbonate, imposing a significant energy penalty arising from separating CO 2 from the anode gas outlets. Here we report a CO 2 electrolyzer uses a bipolar membrane (BPM) to convert (bi)carbonate back to CO 2 , preventing crossover; and that surpasses the single-pass utilization (SPU) limit (25% for multi-carbon products, C 2+ ) suffered by previous neutral-media electrolyzers. We employ a stationary unbuffered catholyte layer between BPM and cathode to promote C 2+ products while ensuring that (bi)carbonate is converted back, in situ, to CO 2 near the cathode. We develop a model that enables the design of the catholyte layer, finding that limiting the diffusion path length of reverted CO 2 to ~10 μm balances the CO 2 diffusion flux with the regeneration rate. We report a single-pass CO 2 utilization of 78%, which lowers the energy associated with downstream separation of CO 2 by 10× compared with past systems. In the carbon dioxide (CO 2 ) to multicarbon electrolysis, the crossover CO 2 to the oxygen-rich anodic gas stream add a further energy-intensive chemical separation step. Here, the authors demonstrate a bipolar membrane-based electrolyzer design that eliminates the crossover CO2.

Electrochemical CO 2 reduction (CO 2 R) is an approach to closing the carbon cycle for chemical synthesis. To date, the field has focused on the electrolysis of ambient pressure CO 2 . However, industrial CO 2 is pressurized—in capture, transport and storage—and is often in dissolved form. Here, we find that pressurization to 50 bar steers CO 2 R pathways toward formate, something seen across widely-employed CO 2 R catalysts. By developing operando methods compatible with high pressures, including quantitative operando Raman spectroscopy, we link the high formate selectivity to increased CO 2 coverage on the cathode surface. The interplay of theory and experiments validates the mechanism, and guides us to functionalize the surface of a Cu cathode with a proton-resistant layer to further the pressure-mediated selectivity effect. This work illustrates the value of industrial CO 2 sources as the starting feedstock for sustainable chemical synthesis. Electroreduction of pressurized CO 2 to chemicals has great potential but remains underexplored. Here, the authors show that increased CO 2 coverage under high pressures alters product selectivity. Guided by the results, a proton-resistant Cu/polypyrrole electrode is designed for enhanced CO 2 conversion.