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The viability of the electrolysis of water currently relies on expensive catalysts such as Pt that are far too impractical for industrial-scale use. Thus, there is considerable interest in developing low-cost, earth-abundant nanomaterials and their alloys as a potential alternative to existing standard catalysts. To address this issue, a synergistic approach involving theory and experiment was carried out. The former, based on density functional theory, was conducted to guide the experiment in selecting the ideal dopant and optimal concentration by focusing on 3d, 4d, and 5d elements as dopants on Ni (001) surface. Subsequently, a series of Ni_1−xCr_x(x= 0.01–0.09) alloy nanocrystals (NCs) with size ranging from 8.3 ± 1.6–18.2 ± 3.2 nm were colloidally synthesized to experimentally investigate the hydrogen evolution reaction (HER) activity. A compositional dependent trend for electrocatalytic activity was observed from both approaches with Ni_0.92Cr_0.08NCs showed the lowest ΔG_Hvalue and the lowest overpotential (η₋₁₀) at −10 mA cm⁻²current density (j), suggesting the highest HER activity among all compositions studied. Among alloy NCs, the highest performing Ni_0.92Cr_0.08composition displayed a mixed Volmer–Heyrovsky HER mechanism, the lowest Tafel slope, and improved stability in alkaline solutions. This study provides critical insights into enhancing the performance of earth-abundant metals through doping-induced electronic structure variation, paving the way for the design of high-efficiency catalysts for water electrolysis. 

Electrocatalytic water splitting presents an exciting opportunity to produce environmentally benign hydrogen fuel to power human activities. Earth abundant Ni5P4 has emerged as an efficient catalyst for the hydrogen evolution reaction (HER) and its activity can be enhanced by admixing synergistic metals to modify the surface affinity and consequently kinetics of HER. Computational studies suggest that the HER activity of Ni5P4 can be improved by Zn doping, causing a chemical pressure-like effect on Ni3 hollow sites. Herein, we report a facile colloidal route to produce Ni5-xZnxP4 nanocrystals (NCs) with control over structure, morphology, and composition and investigate their composition-dependent HER activity in alkaline solutions. Ni5-xZnxP4 NCs retain the hexagonal structure and solid spherical morphology of binary Ni5P4 NCs with a notable size increase from 9.2-28.5 nm for x = 0.00-1.27 compositions. Elemental maps affirm the homogeneous ternary alloy formation with no evidence of Zn segregation. Surface analysis of Ni5-xZnxP4 NCs indicates significant modulation of the surface polarization upon Zn incorporation resulting in a decrease in Niδ+ and an increase in Pδ- charge. Although all compositions followed a Volmer-Heyrovsky HER mechanism, the modulated surface polarization enhances the reaction kinetics producing lower Tafel slopes for Ni5-xZnxP4 NCs (82.5-101.9 mV/dec for x = 0.10-0.84) compared to binary Ni5P4 NCs (109.9 mV/dec). Ni5-xZnxP4 NCs showed higher HER activity with overpotentials of 131.6-193.8 mV for x = 0.02-0.84 in comparison to Ni5P4 NCs (218.1 mV) at a current density of -10 mA/cm2. Alloying with Zn increases the material’s stability with only a ~10% increase in overpotential for Ni4.49Zn0.51P4 NCs at -50 mA/cm2, whereas a ~33% increase was observed for Ni5P4 NCs. At current densities above -40 mA/cm2, bimetallic NCs with x = 0.10, 0.29, and 0.51 compositions outperformed the benchmark Pt/C catalyst, suggesting that hexagonal alloyed Ni5-xZnxP4 NCs are excellent candidates for practical applications that necessitate lower HER overpotentials at higher current densities. 

Size-confined Si nanorods (NRs) have gained notable interest because of their tunable photophysical properties that make them attractive for optoelectronic, charge storage, and sensor technologies. However, established routes for fabrication of Si NRs use well-defined substrates and/or nanoscopic seeds as promoters that cannot be easily removed, hindering the investigation of their true potential and physical properties. Herein, we report a facile, one-step route for the fabrication of Si NRs via thermal disproportionation of hydrogen silsesquioxane (HSQ) in the presence of a molecular tin precursor (SnCl4) at a substantially lower temperature (450 ºC) compared to those used in the synthesis of size-confined Si nanocrystals (>1000 ºC). The use of these precursors allows the facile isolation of phase pure Si NRs via HF etching and subsequent surface passivation with 1-dodecene via hydrosilylation. The diameters (7.7–16.5 nm) of the NRs can be controlled by varying the amount of SnCl4 (0.2–3.0%) introduced during the HSQ synthesis. Physical characterization of the NRs suggests that the diamond cubic structure is not affected by the SnCl4, HF etching, and hydrosilylation. Surface analysis of NRs indicates the presence of Si0 and Sin+ species, which can be attributed to core Si and surface Si species bonded to dodecane ligands, respectively, and a systematic variation of Si0: Si-C ratio with the NR diameter. The NRs show strong size confinement effects with solid-state absorption onsets (2.51–2.80 eV) and solution-state (Tauc) indirect energy gaps (2.54–2.70 eV) that can be tuned by varying the diameters (16.5–7.7 nm), respectively. Photoluminescence (PL) and time-resolved PL (TRPL) studies reveal size-dependent emission (1.95–2.20 eV) with short, nanosecond lifetimes across the visible spectrum which trend closely to absorption trends seen in solid-state absorption data. The facile synthesis developed for size-confined Si NRs with high crystallinity and tunable optical properties will promote their application in optoelectronic, charge storage, and sensing studies.