Low Precursor Concentration Research Articles

Unravelling the critical role of electrochemical deposition parameters in determining cycling reversibility of alpha-nickel hydroxide in alkaline electrolyte

Nickel hydroxide (α-Ni(OH)2) with large interlayer spacing is a promising pseudocapacitive material with high theoretical capacitance and good rate capability. However, the phase transition reversibility between α-Ni(OH)2 and γ-NiOOH in alkaline electrolyte upon charging/discharging is still vague. In this study, the cycling reversibility of α-Ni(OH)2 has been systematically investigated via adjusting the electrochemical deposition parameters. Structure characterizations and electrochemical analysis clearly revealed that the precursor concentration, deposition voltage and time significantly affect the mass loading of active material, the thicknesses of deposited films and their morphologies. Increasing the precursor concentration, deposition voltage and time lead to high mass loading, thick film and agglomerated nanosheets, which deteriorated the charge transfer and ion diffusion that lead to inferior cycling reversibility. In contrast, thin film with small mass loading and vertically-aligned nanosheets can be obtained upon deposition under low precursor concentration, small deposition voltage and short time, which shows facilitated charge transfer, ion diffusion and thereby high phase transition reversibility. Therefore, choosing appropriate deposition parameters would be beneficial to improve the electrode's cycling reversibility, which can effectively guide the development of more metal hydroxides with enhanced charge storage capability.

Phase changes in burning precursor-laden single droplets leading to puffing and micro-explosion

When producing metal-oxide nanoparticles via flame spray pyrolysis, precursor-laden droplets are ignited and undergo thermally induced disintegration, called ‘puffing’ and ‘micro-explosion’. In a manner that is not fully understood, these processes are associated with the formation of dispersed phases inside the droplets. This work aims at visualizing the interior of precursor-laden burning single droplets via diffuse back illumination and microscopic high-speed imaging. Solutions containing iron(III) nitrate nonahydrate (INN) and tin(II) 2-ethylhexanoate (Sn-EH) were dispersed into single droplets of sub-100 μm diameter that were ignited by passing through a heated coil. At low precursor concentration, 50% of the INN-laden droplets indicate a gas bubble of about 5 μm diameter in the center of the droplet. The bubble persists for several hundred microseconds at a similar size. In almost all of these cases, the bubble expands at some point and the droplet ends up in a micro-explosion. In some of these instances, the droplet’s surface shows spatial brightness modulations, i.e., surface undulations, indicating the formation of a viscous shell. With increasing INN concentration, the fraction of droplets showing surface undulations, gas bubbles, and micro-explosions drastically decreases. This may be associated with a more rigid viscous shell and reduced mobility of bubbles. Bright incandescent streaks originating from the disrupting INN-laden droplets, may indicate sub-micrometer droplets or particles from within the droplets or formed in the gas phase. In contrast, Sn-EH-laden droplets show very fast disruptions, typically less than 10 μs from first visible deformation to ejection of secondary droplets. Bubbles and surface undulations were not observed.Graphical abstract

Tailoring the Wettability of Bacterial Cellulose Magnetobots via the Assembly of In Situ Synthesized and Surfactant-Coated Magnetic Nanoparticles.

This study showcases the possibility of tailoring the wettability of magnetic bacterial cellulose (m-BC) composites by the combined effect of in situ synthesized magnetic nanoparticles (MNPs) distribution and simultaneous oleic acid (OA) coating within the BC matrix. This combined effect of MNPs and OA resulted in m-BC composites exhibiting solvent-dependent and time-dependent surface-wetting behavior, which was not observed in either individual cases of BC that have been modified with OA or BC that has MNPs adsorbed on its fibers. This tailored wettability in m-BCs was achieved via varying the concentrations of iron precursors, which governed the arrangement and morphology of MNPs (uniformly or clustered) on the BC membrane, although the same fraction of MNPs was observed in both the m-BCs. Finally, we have achieved delayed water absorption in m-BC_x (synthesized in a comparatively lower precursor concentration) and no absorption of water in m-BC_4x (synthesized in a 4-times-higher precursor concentration). The m-BC_4x composite maintained its hydrophobic characteristics in diverse environments, ranging from highly acidic conditions (pH 1.2) to physiological environments at pH 4, 5.5, and 7.4. The MNP agglomerates on the BC nanofibers in the m-BC_4x composite were found to be instrumental in attaining a stable cyclic absorption performance with structural integrity. Additionally, the magnetic-inducing heat generation efficiency of the m-BCs can be extended for evaporating low-boiling-point solvents. The present study expands the frontiers of BC-based magnetic composites by emphasizing the assembly of surfactant-coated magnetic nanostructures in their responsiveness to polar/nonpolar liquids with stable performance even in complex scenarios.

Modern Smart Street Light Monitoring Systems

Abstract: This study highlights the importance of Modern Street light control systems over traditional ones, with LED lamps emerging as the most suitable choice due to their advantagessuch as reduced heat production, lower electricity consumption, and extended lifespan. The main goal is to enhance system efficiency by minimizing unnecessary electricity loss during daylight and when lighting is not required. Automating street lights using LDR and PIR sensorsin conjunction with Arduino Uno offers a costeffective and secure solution, eliminating the drawbacks of manual switching and simplifying cost reduction and maintenance. Additionally,applying a ZnO coating to the street light casings provides effective protection against dust and moisture, resulting in efficient lighting. The process involves sol-gel deposition of ZnO nanoparticles on silica glass substrates, followed by preannealing and repeated dip coating. Annealing at temperatures between 450°C and 600°C further improves the results. The uniformand defect-free coatings are confirmed by SEM images, while transmission spectra reveal over80% penetration of visible light (400 nm to 900 nm). Lower precursor concentrations lead to better penetration of light below 300 nm wavelength.

Sub-second ultrafast yet programmable wet-chemical synthesis

Wet-chemical synthesis via heating bulk solution is powerful to obtain nanomaterials. However, it still suffers from limited reaction rate, controllability, and massive consumption of energy/reactants, particularly for the synthesis on specific substrates. Herein, we present an innovative wet-interfacial Joule heating (WIJH) approach to synthesize various nanomaterials in a sub-second ultrafast, programmable, and energy/reactant-saving manner. In the WIJH, Joule heat generated by the graphene film (GF) is confined at the substrate-solution interface. Accompanied by instantaneous evaporation of the solvent, the temperature is steeply improved and the precursors are concentrated, thereby synergistically accelerating and controlling the nucleation and growth of nanomaterials on the substrate. WIJH leads to a record high crystallization rate of HKUST-1 (~1.97 μm s−1), an ultralow energy cost (9.55 × 10−6 kWh cm−2) and low precursor concentrations, which are up to 5 orders of magnitude faster, −6 and −2 orders of magnitude lower than traditional methods, respectively. Moreover, WIJH could handily customize the products’ amount, size, and morphology via programming the electrified procedures. The as-prepared HKUST-1/GF enables the Joule-heating-controllable and low-energy-required capture and liberation towards CO2. This study opens up a new methodology towards the superefficient synthesis of nanomaterials and solvent-involved Joule heating.

Kinetics and product identification of water-dissolved nitroguaiacol photolysis under artificial sunlight.

Nitroguaiacols are typical constituents of biomass-burning emissions, including absorbing aerosols which contribute to climate change. Although they are also harmful to humans and plants, their atmospheric fate and lifetimes are still very speculative. Therefore, in this work, the photolysis kinetics of aqueous-phase 4-nitroguaiacol (4NG) and 5-nitroguaiacol (5NG), and the resulting photo-formed products were investigated under artificial sunlight, observing also the effect of sunlight on the absorption properties of the solutions. We found the photolysis of 5NG slower than that of 4NG, whereas the absorbance in the visible range prevailed in the 5NG solutions at the end of experiments. Although we identified dinitroguaiacol as one of the 4NG photolysis products, which increased light absorption of 4NG-containing solutions, considerably more chromophores formed in the 5NG photolyzed solutions, implying its stronger potential for secondary BrC formation in the atmosphere. In general, denitration, carbon loss, hydroxylation, nitration, and carbon gain were characteristic of 4NG phototransformation, while carbon loss, hydroxylation, and carbon gain were observed in the case of 5NG. The photolysis kinetics was found of the first order at low precursor concentrations (<0.45mM), resulting in their lifetimes in the order of days (125 and 167h illumination for 4NG and 5NG, respectively), which suggests long-range transport of the investigated compounds in the atmosphere and proposes their use as biomass-burning aerosol tracer compounds.

Chemically reduced graphene oxide based aerogels - Insight on the surface and textural functionalities dependent on handling the synthesis factors

Efficient adjusting of reduced graphene oxide aerogels properties requires information about experimental factor-aerogel property relationship. In this work, the reduced graphene oxide aerogels surface and textural functionalities in relation to precursor concentration, gelation time and hydrogel freezing temperature were studied in detail, with the use of dynamic adsorption method of gaseous organic probes and experimental design. The precursor concentration and the hydrogel freezing temperature have the strongest influence on textural properties - a negative correlation with apparent surface area was observed. The highest value of 229.36 m2 g−1 was obtained for samples synthesized at the lowest concentration of precursor (2 mg mL−1) and hydrogel freezing temperature (−196 °C). Low precursor concentration promote formation of more hydrophobic aerogels. All aerogels display tendencies for dispersive, dipole-type and electron donor interactions. Moreover, a repulsion of electron lone pairs was observed, as well as shape-based selectivity (originating from porosity and surface roughness) in gas-solid adsorption process. Analysis of the free surface energy revealed that the maximum value (193.21 mJ m−2) is obtained at 7.2 mg mL−1 precursor concentration, − 104 °C hydrogel freezing temperature and 23 h gelation time. Presented findings can translate directly into reduced graphene oxide aerogels tailored for specific applications such as adsorption or catalysis.

Numerical investigation of pyrolysis coking characteristics of supercritical hydrocarbon fuels in sinusoidal cooling channels

Carbon deposits in the high-temperature cooling channels of aero engines can lead to severe heat transfer deterioration. So it is significant to reduce the amount of carbon deposit and thus improve the safety of aero-engine operation. In this paper, a two-dimensional axisymmetric CFD model with coupled pyrolysis and coking reactions is developed, and the unsteady formation of carbon is directly simulated by the dynamic mesh technique. The pyrolysis, coking, flow and heat transfer characteristics of supercritical n-decane in smooth and sinusoidal channels during heated for 20 min were studied comparatively. The results show that the coking mass in the sinusoidal channel is basically maintained at 66% of the smooth channel, and the coking layer thickness was relatively declined by 20 μm, which is attributed to the lower precursor concentration and wall temperature in the sinusoidal channel. Specifically, due to a thinner boundary layer and a larger heat transfer area, the maximum difference in fuel conversion rate is 24.4%, with a maximum increase in Nu of 70 and a relative decrease in wall temperature of 85 K. Besides, the flow characteristics are mainly reflected in a significant increase in turbulence at the expense a pressure drop of 15.74 kPa.

In-situ monitored chemical bath deposition of planar NiO layer for inverted perovskite solar cell with enhanced efficiency

• A solution route of chemical bath deposition (CBD) planar NiO x film was first proposed as the efficient hole transport layer for the inverted PSCs • Through an in-situ monitoring of the CBD reaction process, the morphologies and semiconducting properties of the NiO x film can be adjusted by the concentration variation of [Ni(H 2 O) x (NH 3 ) 6-x ] 2+ cation. • The devices based on planar NiO x at 50°C and C0.5 concentration achieved an enhanced efficiency to from 16.14% to 18.17%. As a convenient, low-cost and up-scalable solution route, chemical bath deposition (CBD) has exhibited impressive advantages in fabricating electron transporting materials like SnO 2 , achieving record efficiencies for regular n-i-p perovskite solar cells (PSCs). However, for the hysteresis-free and potentially more stable inverted p-i-n PSCs, CBD processing is rarely studied to improve the device performance. In this work, we first present a CBD planar NiO x film as the efficient hole transport layer for the inverted perovskite solar cells (IPSCs). The morphologies and semiconducting properties of the NiO x film can be adjusted by varying the concentration of [Ni(H 2 O) x (NH 3 ) 6- x ] 2+ cation via in-situ monitoring of the CBD reaction process. The characterizations of ultraviolet photoelectron spectroscopy, transient absorption spectroscopy, time-resolved photoluminescence suggest that the CBD planar NiO x film possesses enhanced conductivity and aligned energy band levels with perovskite, which benefits for the charge transport in the IPSCs. The devices based on planar NiO x at 50°C and low nickel precursor concentration achieved an enhanced efficiency from 16.14% to 18.17%. This work established an efficient CBD route to fabricate planar NiO x film for PSCs and paved the way for high performance PSCs with CBD-prepared hole transporting materials.

Secondary organic aerosol formation from mixed volatile organic compounds: Effect of RO2 chemistry and precursor concentration

Secondary organic aerosol (SOA) plays a significant role in contributing to atmospheric fine particles, as well as in global air quality and climate. However, the current understanding of the atmospheric formation of SOA and its simulation is still highly uncertain due to the complexity of its precursor VOCs. In our study, SOA formation in different mixed VOC scenarios was investigated using a 30 m3 indoor smog chamber. By comparing SOA formation in individual VOC scenarios, it was found that SOA yield from anthropogenic VOCs (AVOCs) can be positively (+83.9%) affected by coexisting AVOCs, while inhibited (−51.4%) by the presence of isoprene, via the OH scavenging effect. The cross-reactions of peroxyl radical (RO2) generated from different AVOCs were proved to be the main contributor (up to 39.0%) to SOA formation, highlighting the importance of RO2 + RʹO2 reactions in mixed VOC scenarios. Meanwhile, the formation of gas-phase organic intermediates of different volatility categories from the RO2 reactions was also affected by the precursor concentration, and a higher SOA yield was found at lower precursor concentrations due to the larger contribution of intermediates with lower volatility. Our study provides new insights into SOA formation by considering the interactions between intermediate products from mixed VOCs.

Influence of thickness and morphology of MoS2 on the performance of counter electrodes in dye-sensitized solar cells.

Non-platinum electrodes for photoelectric devices are challenging and attractive to the scientific community. A thin film of molybdenum disulfide (MoS2) was prepared on substrates coated with fluorine-doped tin oxide (FTO) to substitute the platinum counter electrode (CE) for dye-sensitized solar cells (DSSCs). Herein, we synthesized layered and honeycomb-like MoS2 thin films via the cyclic voltammetry (CV) route. Thickness and morphology of the MoS2 thin films were controlled via the concentration of precursor solution. The obtained results showed that MoS2 thin films formed at a low precursor concentration had a layered morphology while a honeycomb-like MoS2 thin film was formed at a high precursor concentration. Both types of MoS2 thin film were composed of 1T and 2H structures and exhibited excellent electrocatalytic activity for the I3–/I− redox couple. DSSCs assembled using these MoS2 CEs showed a maximal power conversion efficiency of 7.33%. The short-circuit value reached 16.3 mA·cm−2, which was higher than that of a conventional Pt/FTO CE (15.3 mA·cm−2). This work reports for the first time the possibility to obtain a honeycomb-like MoS2 thin film morphology by the CV method and investigates the effect of film structure on the electrocatalytic activity and photovoltaic performance of CEs for DSSC application.

Open-air plasma deposition of polymer-supported silica-based membranes for gas separation

In this study, we developed an open-air atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) as a scalable technique to fabricate polymer-supported silica-based membranes for gas separation. Using the open-air AP-PECVD, we achieved a low-temperature deposition of silica-based molecular sieve membranes onto porous polymeric support in a system that can operate under open-air conditions. We investigated the effect of deposition conditions, such as precursor concentration and deposition temperature, on the membrane structure and permeation property. It was revealed that precursor concentration plays a vital role in determining membrane properties. The membranes prepared with low precursor concentration had an inorganic structure with granular morphology, resulting in poor permselective performance. In contrast, deposition at high precursor concentration led to the formation of a continuous layer with a silicone-like structure. By optimizing the precursor concentration, a membrane having a He permeance of 7.25 × 10−8 mol/(m2 s Pa) with a He/SF6 permeance ratio of 171 can be fabricated at room temperature. The deposition at elevated temperature was also effective in improving the permselective performance. By increasing the deposition temperature to 150 °C, the permselective performance of the membrane was improved to a He permeance of 7.7 × 10−8 mol/(m2 s Pa) and He/SF6 of 434. The resultant membranes also exhibited high selectivity for the separation of industrial relevant gas mixtures such as H2/N2 and H2/CH4 with the permeance ratios of 40 and 38, respectively. The present study demonstrates that open-air AP-PECVD is promising as a scalable technique to fabricate polymer-supported silica-based membranes with high productivity.

Characterization of Fractal Structures by Spray Flame Synthesis Using X-ray Scattering.

In this work, we take on an in-depth characterization of the complex particle structures made by spray flame synthesis. Because of the resulting hierarchical aggregates, very few measurement techniques are available to analyze their primary particle and fractal properties. Therefore, we use small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) to investigate the influence of the precursor concentration on the fractal structures of zirconia nanoparticles. The combination of information gained from these measurement results leads to a detailed description of the particle system, including the polydispersity and size distribution of the primary particles. Based on our findings, unstable process conditions could be identified at low precursor concentrations resulting in the broadest size distribution of primary particles with rough surfaces. Higher precursor concentrations lead to reproducible primary particle sizes almost independent of the initial precursor concentration. Regarding the fractal properties, the typical shape of aggregates for aerosols is present for the investigated range of precursor concentrations. In conclusion, the consistent results for SAXS and TEM show a conclusive characterization of a complex particle system, allowing for the identification of the underlying particle formation mechanism.

Asymmetric seed passivation for regioselective overgrowth and formation of plasmonic nanobowls.

Plasmonic nanoparticles (NPs) have garnered excitement over the past several decades stemming from their unique optoelectronic properties, leading to their use in various sensing applications and theranostics. Symmetry dictates the properties of many nanomaterials, and nanostructures with low, but still defined symmetries, often display markedly different properties compared to their higher symmetry counterparts. While numerous methods are available to manipulate symmetry, surface protecting groups such as polymers are finding use due to their ability to achieve regioselective modification of NP seeds, which can be removed after overgrowth as shown here. Specifically, poly(styrene-b-polyacrylic acid) (PSPAA) is used to asymmetrically passivate cubic Au seeds through competition with hexadecyltrimethylammonium bromide (CTAB) ligands. The asymmetric passivation via collapsed PSPAA causes only select vertices and faces of the Au cubes to be available for deposition of new material (i.e., Au, Au-Ag alloy, and Au-Pd alloy) during seeded overgrowth. At low metal precursor concentrations, deposition follows observations from unpassivated seeds but with new material growing from only the exposed seed portions. At high metal precursor concentrations, nanobowl-like structures form from interaction between the depositing phase and the passivating PSPAA. Through experiment and simulation, the optoelectronic properties of these nanobowls were probed, finding that the interiors and exteriors of the nanobowls can be functionalized selectively as revealed by surface enhanced Raman spectroscopy (SERS).

Synthesis mechanism and phase stability analysis of z‐Y2Si2O7 by sol‐gel process

AbstractSynthesis mechanism and phase stability analysis of square z‐Y2Si2O7 was studied in this research by using Y(NO3)3·6H2O and tetra ethoxy orthosilicate as precursors. The concentration of the precursor directly affects the degree of hydrolysis of tetra ethoxy orthosilicate and the uniformity of the gel by Fourier transform infrared spectral analysis. The thermogravimetric analysis shows that the crystallization temperature of the precursor decreases gradually with the decrease of precursor concentration. Because the low precursor concentration is beneficial to the formation of the homogeneous molecular level of yttrium silica network gel. Finally, the crystallized z‐Y2Si2O7 was detected by X‐ray diffraction and further verified by a transmission electron microscope after calcining at 800°C. The maximum stable temperature of z‐Y2Si2O7 was less than 1050°C. The microscopic morphology of z‐Y2Si2O7 is square nanoparticles. The grain size of z‐Y2Si2O7 increases with the decrease of precursor concentration.

Computational fluid dynamics modeling and analysis of silica nanoparticle synthesis in a flame spray pyrolysis reactor

Flame Spray Pyrolysis (FSP) is a method for large-scale production of nanoparticles and nanoscale powders employed in a wide range of industrial applications. Particle size and morphology are complex functions of the physicochemical phenomena occurring in the FSP reactor. An extensive study of FSP-related phenomena can be utilized to develop effective strategies for achieving desired particle size/morphology and scaling up the overall yield of an FSP system. In this work, a computational fluid dynamics (CFD) model of an FSP reactor is developed to simulate the coupling of key phenomena involved in the particle synthesis process: liquid spray breakup and evaporation, mixing, combustion, and particle formation/growth of silica nanoparticles. The particle sizes and their distributions from the CFD simulations are validated against experimental data. Subsequently, the simulations are utilized to investigate the impact of process parameters on the resultant flame dynamics and particle growth. Firstly, the CFD results show that the particle sizes are strongly correlated with the precursor concentration in the solvent. At lower precursor concentrations, the spread of the distribution is relatively insensitive to the value of the concentration. At higher concentrations, the spread is higher as the collision probability between particles is higher. Secondly, increasing the pilot flow rate increases the length of the pilot flames impacting the local ignition location of the spray flame. Lastly, it is shown that the dispersion gas flow rate strongly influences the spray flame shape. This shape can be used for control of particle growth as it helps determine the regions of high temperature and the residence time of the particles in the high temperature region enabling the design and process optimization of the FSP reactor.

Fabrication of tin‐doped hematite modified with NiFe‐LDH nanoflakes for highly efficient solar water splitting

Photoelectrochemical (PEC) water splitting is widely regarded as an effective process for sustainable storage of solar energy as chemical energy in the form of H2. The efficiency of this process depends upon the light absorption, charge injection, and charge separation efficiency of the photoanode material used. In this work, doping hematite with 1% tin and loading with NiFe-layered double hydroxide (LDH) co-catalyst has been done to improve the charge transport properties. To enhance the PEC performance and study the effect of precursor concentration, NiFe-LDH at two different concentrations (low and high) was coated on Sn-doped hematite. A high photocurrent density ca. 2.9 mA/cm2 at 1.8 V vs reversible hydrogen electrode (RHE) and a 170 mV cathodic shift in onset potential compared to pristine hematite (0.22 mA/cm2 at 1.8 V vs RHE) was recorded for Sn-doped hematite coated with low precursor concentration. The enhanced PEC activity can be attributed to the synergistic effect of Sn doping and NiFe-LDH co-catalyst on hematite, which contributes to an efficient separation of the photogenerated charge carriers and reduces hole accumulation at the surface. However, for the high precursor concentration case, the formation of a thick film of NiFe-LDH results in a comparatively lower current density (0.85 mA/cm2 at 1.8 V vs RHE). The results obtained show that NiFe-LDH can be used as an effective co-catalyst to significantly enhance the charge transport properties of tin-doped hematite. A charge transfer mechanism of the developed photoanodes is also discussed in detail.

Sub- μ m features patterned with laser interference lithography for the epitaxial lateral overgrowth of α-Ga2O3 via mist chemical vapor deposition

The low growth rate of mist chemical vapor deposition normally requires a long growth time to achieve coalescence in the epitaxial lateral overgrowth of α-Ga2O3 thin films on sapphire substrates. To address this issue, sub-μm features were patterned using laser interference lithography. Periodical stripes with a ∼590-nm pitch allowed the overgrowth of crack-free, void-free, and continuous thin films, while typical growth conditions using a low carrier gas flow rate and a low Ga precursor concentration were maintained. Coalescence was achieved even with a short growth time of &amp;lt;30 min and a low film thickness of &amp;lt;500 nm. Transmittance and x-ray diffraction spectra show that the film was predominantly in α-phase. Transmission electron microscopy (TEM) images reveal cup-top-like α-Ga2O3 regions of low dislocation density on the SiOx mask. Selected area electron diffraction and high-resolution TEM analyses confirm that an α-Ga2O3 layer was formed even on the top of the SiOx mask. Interestingly, the dislocations formed on the window areas did not bend toward the center of the masks; rather, a dislocation bending outward from the center was observed. This suggests the occurrence of early coalescence and/or atomic rearrangement.

Lamellar Enzyme-Metal–Organic Framework Composites Enable Catalysis on Large Substrates

Lamellar Enzyme-Metal–Organic Framework Composites Enable Catalysis on Large Substrates

Kinetic-Controlled Growth of Bi Nanostructures for Electrocatalytic CO2 Reduction

Bi-based catalysts have attracted great attention for efficient electrocatalytic carbon dioxide (CO2) reduction to formic acid (HCOOH). However, the effect of the growth kinetics of Bi nanostructures on morphology and their catalytic performance has not been studied. Here, we varied the Bi3+ precursor concentration in the electrolyte to control the electrochemical growth rate of Bi nanostructures. It was found that the growth rate determines not only the geometric structure but also the microstructure of Bi nanostructures. The slow growth with a low precursor concentration (1 mM) produced Bi nano-sheet (NS) with high crystallinity in (012) preferred orientation. But, the polycrystalline Bi nano-branch (NB) with a larger surface area was formed by a faster growth condition (precursor concentration = 30 mM). As a result, Bi NB achieved a higher FEHCOOH of 97.1% than Bi NS (FEHCOOH = 81.5%) at −1.0 VRHE. This work reveals that the growth condition of the Bi nanostructures plays a significant role in designing the catalysts for the efficient CO2 reduction reaction.