Green Hydrogen Production: From Water Electrolysis to Industrial Scale

Green hydrogen is hydrogen gas (H2) produced from renewable energy sources such as solar, wind, or hydropower through water electrolysis. Unlike grey hydrogen (from natural gas via steam reforming) and blue hydrogen (with carbon capture), green hydrogen offers zero direct CO2 emissions, making it a critical enabler of net-zero pathways across refineries, fertilizer production, steelmaking, and mobility.

Core Concepts

Water Electrolysis: The process splits water (H2O) using electricity: 2H2O + electricity → 2H2 + O2. Electrolyzer types include Polymer Electrolyte Membrane (PEM), Alkaline, and Solid Oxide Electrolyzers (SOEC), each with different efficiency and operational characteristics.

Current Cost vs. Targets: Green hydrogen currently costs $4-8 per kg; targets by 2030 are $2-3/kg to achieve cost parity with grey hydrogen in energy-intensive applications.

Electrolyzer Technology & Efficiency: PEM electrolyzers operate at 55-65% electrical efficiency and support dynamic operation aligned with variable renewable supply. Alkaline electrolyzers (65-75% efficiency) are more mature and cost-effective but less flexible. SOEC technology (up to 80-90% at higher temperatures) is in demonstration phase.

Renewable-to-H2 Systems: Integration requires co-locating electrolysers with renewable power plants (solar/wind) or connecting to grids with high renewable penetration. Power-to-Hydrogen (P2H) concepts are emerging in Europe, India, and the Middle East.

Demand Pull: Industrial hydrogen demand is ~75 million tonnes annually; replacing grey hydrogen in refineries (40% of use) and ammonia synthesis (50% of use) represents ~60 million tonnes of potential green H2 displacement.

Policy & Investment: India's National Green Hydrogen Mission (2022) targets 5 MMT of green hydrogen and 125 GW dedicated renewable capacity by 2030. EU, Japan, South Korea also announced ambitious targets.

Research Frontiers

Anode & Cathode Materials: Novel catalysts (e.g., non-precious metal catalysts) and electrode architectures to reduce capital costs of electrolysers by 50-70%.

Thermochemical Water Splitting: High-temperature solar concentrators paired with cyclic redox reactions to produce hydrogen directly without intermediate electricity; efficiency potential of 25-50%.

Proton Exchange Membrane (PEM) Durability: Operating lifetimes of 50,000+ hours under cycling conditions require advances in ionomer and catalyst layer stability.

Hybrid Systems: Coupling electrolysis with algae or biomass gasification for consolidated green hydrogen + biochar or bio-products.

Conclusion

Green hydrogen represents a pivotal decarbonisation lever for heavy industry, with PEM and alkaline technologies mature enough for commercial deployment. Cost reduction and renewable-to-hydrogen integration will define the transition trajectory.

Keywords: Green hydrogen, water electrolysis, renewable energy, PEM electrolyzer, alkaline electrolyzer, net-zero hydrogen, decarbonisation, industrial hydrogen

Sustainable Aviation Fuel (SAF) Scale-up: From Lab to Commercial Aviation

Aviation accounts for approximately 2-3% of global CO2 emissions. Sustainable Aviation Fuel (SAF) represents a critical pathway to decarbonise the sector and achieve net-zero targets by 2050. SAF is a drop-in replacement for conventional jet fuel (Jet A-1) produced from sustainable feedstocks including waste oils, agricultural residues, and synthetic pathways.

Key Concepts

SAF can be produced through multiple pathways: HEFA (Hydroprocessed Esters and Fatty Acids), ATJ (Alcohol-to-Jet), and Power-to-Liquids (PtL). Each pathway involves different feedstock-to-fuel conversion chemistry with varying maturity levels. HEFA technology is the most commercially mature, while ATJ and PtL remain in pilot and early-commercial phases.

HEFA Technology: The HEFA process hydroprocesses used cooking oils and other lipids, removing oxygen and producing hydrocarbons equivalent to conventional jet fuel. This pathway can reduce lifecycle greenhouse gas (GHG) emissions by 50-80% compared to fossil jet fuel.

ATJ Technology: Alcohol-to-Jet converts ethanol (from biomass or bio-based routes) via dehydration, oligomerisation, and hydrogenation. The process offers flexibility in feedstock sourcing but requires careful control of intermediate product quality.

Power-to-Liquids: Synthetic pathways combining hydrogen (from renewable electricity) and CO2 (from capture or biomass) to produce SAF. This pathway shows promise for hard-to-abate sectors but faces scaling challenges.

Policy & Market: Global SAF demand is expected to reach 6-10 million tonnes annually by 2030, driven by regulatory mandates (ICAO's Carbon Offsetting and Reduction Scheme for International Aviation) and corporate net-zero commitments. SAF currently costs 2-3x more than conventional jet fuel, requiring investment in scale and R&D.

Applications & Research Frontiers 

Co-processing SAF production within existing refinery infrastructure offers capital efficiency advantages but requires compatibility assessments with existing hydrotreating units.

Advanced sustainability metrics beyond GHG accounting: Life cycle assessment (LCA) frameworks increasingly incorporate water stress, biodiversity impact, and social criteria for feedstock sourcing.

Engine performance and compatibility testing remains critical—SAF blends up to 50% are already approved, with research ongoing to achieve higher concentrations and improve lubricity characteristics.

Feedstock diversification strategies are essential: advanced feedstocks (algae, synthetic biology routes) under development to reduce pressure on traditional biomass supplies.

Conclusion

SAF represents a tangible near-term solution for aviation decarbonisation, with HEFA established and ATJ/PtL emerging. Success requires integrated efforts across policy, infrastructure investment, and feedstock development.

Keywords: Sustainable Aviation Fuel, SAF, HEFA, Alcohol-to-Jet, aviation decarbonisation, net-zero, renewable fuels, biofuels, lifecycle assessment

The Wurtz Reaction: Coupling Alkyl Halides to Form C-C Bonds

Introduction

The Wurtz reaction is a fundamental organic transformation that enables the formation of new carbon-carbon bonds through the coupling of alkyl halides with sodium metal. This classical reaction, discovered by Charles-Adolphe Wurtz in 1855, remains an important tool in synthetic organic chemistry, particularly for the synthesis of alkanes and the construction of larger carbon frameworks.

Definition and Overview

The Wurtz reaction is defined as the coupling of two alkyl halides mediated by sodium metal:

$$2 \text{R-X} + 2 \text{Na} \rightarrow \text{R-R} + 2 \text{NaX}$$

Where:

• R = alkyl group
• X = halogen (Cl, Br, or I)
• Na = sodium metal

Mechanism

The Wurtz reaction proceeds through a radical mechanism involving two main steps:

Step 1: Formation of Alkyl Radical

Sodium metal transfers an electron to the alkyl halide:

$$\text{R-X} + \text{Na} \rightarrow \text{R}^{\bullet} + \text{Na}^{+}\text{X}^{-}$$

Step 2: Carbon-Carbon Bond Formation

Two alkyl radicals couple to form the new C-C bond:

$$\text{R}^{\bullet} + \text{R}^{\bullet} \rightarrow \text{R-R}$$

Practical Examples

Example 1: Formation of Butane

The coupling of two ethyl bromide molecules:

$$2 \text{CH}_{3}\text{CH}_{2}\text{Br} + 2 \text{Na} \rightarrow \text{CH}_{3}\text{CH}_{2}\text{CH}_{2}\text{CH}_{3} + 2 \text{NaBr}$$

SMILES representation:

• Reactant (Ethyl bromide): div data-smiles="CCBr"