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Gold and palladium nanoneedle electrocatalysts benefit from field-induced reagent concentration to improve the efficiency of carbon dioxide reduction in the synthesis of carbon-based fuels using renewable electricity. Boosting CO 2 reduction with nanostructured electrodes Electrochemical reduction of carbon dioxide (CO 2 ) to carbon monoxide is the first step in the manufacture of fuels and feedstocks using renewable electricity, but it is a slow process owing to low CO 2 concentration near the CO 2 reduction sites on the electrocatalysts. Min Liu et al . show that electrodes with sharp nanometre-sized tips produce local high electric fields that increase local CO 2 concentrations near the active electrocatalyst surface. Gold nanoneedles exploiting this field-induced reagent concentration (FIRC) effect outperform the best gold nanoparticles and oxide-derived noble metal catalysts. Similarly, palladium nanoneedle electrocatalsts produce formate from CO 2 with high selectivity and efficiency, proving the wider applicability of the FIRC concept and its value for the design of superior electrocatalysts. Electrochemical reduction of carbon dioxide (CO 2 ) to carbon monoxide (CO) is the first step in the synthesis of more complex carbon-based fuels and feedstocks using renewable electricity 1 , 2 , 3 , 4 , 5 , 6 , 7 . Unfortunately, the reaction suffers from slow kinetics 7 , 8 owing to the low local concentration of CO 2 surrounding typical CO 2 reduction reaction catalysts. Alkali metal cations are known to overcome this limitation through non-covalent interactions with adsorbed reagent species 9 , 10 , but the effect is restricted by the solubility of relevant salts. Large applied electrode potentials can also enhance CO 2 adsorption 11 , but this comes at the cost of increased hydrogen (H 2 ) evolution. Here we report that nanostructured electrodes produce, at low applied overpotentials, local high electric fields that concentrate electrolyte cations, which in turn leads to a high local concentration of CO 2 close to the active CO 2 reduction reaction surface. Simulations reveal tenfold higher electric fields associated with metallic nanometre-sized tips compared to quasi-planar electrode regions, and measurements using gold nanoneedles confirm a field-induced reagent concentration that enables the CO 2 reduction reaction to proceed with a geometric current density for CO of 22 milliamperes per square centimetre at −0.35 volts (overpotential of 0.24 volts). This performance surpasses by an order of magnitude the performance of the best gold nanorods, nanoparticles and oxide-derived noble metal catalysts. Similarly designed palladium nanoneedle electrocatalysts produce formate with a Faradaic efficiency of more than 90 per cent and an unprecedented geometric current density for formate of 10 milliamperes per square centimetre at −0.2 volts, demonstrating the wider applicability of the field-induced reagent concentration concept.

Devices that diagnose and characterize disease have the potential to greatly improve healthcare worldwide. This thesis explores a number of different elements pertaining to device design and application. A microfluidic device for the capture and profiling of circulating tumor cells (CTCs) is tested against a rabbit model of cancer. This device demonstrates both an increase in CTC load and aggressiveness which correlates with traditional computed tomography measurements. CTC biology is also shown to differ markedly from tumour precursor cells. Next, a study of gold microelectrode architecture is performed with the aim of improving performance towards biosensing. A unique regime of gold ion concentration, applied voltage, and electrolyte viscosity is determined which drives the assembly of a highly structured morphology. Further studies illustrate growth mechanisms and the sensitivity of the electrode towards biomolecule detection. Additionally, a microfluidic device for instrument-free manipulation of microscopic fluid quantities is developed. This design allows the metering and dispensing of reagents in an intuitive manner by combining a series of capillary valves and a simple push-button. This “Digit Chip” is applied to the detection of antibacterial susceptibility alongside a simple smart-phone based fluorimeter. Together these studies explore the application of electrochemical and microfluidic modalities to the realm of disease monitoring.

Electrochemical reduction of carbon dioxide (CO ) to carbon monoxide (CO) is the first step in the synthesis of more complex carbon-based fuels and feedstocks using renewable electricity. Unfortunately, the reaction suffers from slow kinetics owing to the low local concentration of CO surrounding typical CO reduction reaction catalysts. Alkali metal cations are known to overcome this limitation through non-covalent interactions with adsorbed reagent species, but the effect is restricted by the solubility of relevant salts. Large applied electrode potentials can also enhance CO adsorption, but this comes at the cost of increased hydrogen (H ) evolution. Here we report that nanostructured electrodes produce, at low applied overpotentials, local high electric fields that concentrate electrolyte cations, which in turn leads to a high local concentration of CO close to the active CO reduction reaction surface. Simulations reveal tenfold higher electric fields associated with metallic nanometre-sized tips compared to quasi-planar electrode regions, and measurements using gold nanoneedles confirm a field-induced reagent concentration that enables the CO reduction reaction to proceed with a geometric current density for CO of 22 milliamperes per square centimetre at -0.35 volts (overpotential of 0.24 volts). This performance surpasses by an order of magnitude the performance of the best gold nanorods, nanoparticles and oxide-derived noble metal catalysts. Similarly designed palladium nanoneedle electrocatalysts produce formate with a Faradaic efficiency of more than 90 per cent and an unprecedented geometric current density for formate of 10 milliamperes per square centimetre at -0.2 volts, demonstrating the wider applicability of the field-induced reagent concentration concept.