Script to generate 'n' ethereum wallets (address + private key) and store it in a JSON. keysDB.json is the example output.

createWallets.js

// Init web3 and configure to a node (alternatively to infura/ganache-cli)
var Web3 = require('web3')
var web3 = new Web3('http://127.0.0.1:8545')

// Setup lowdb to store 
const low = require('lowdb')
const FileSync = require('lowdb/adapters/FileSync')
const adapter = new FileSync('keysDB.json')
const db = low(adapter)
db.defaults({ keys: [], count: 0 }).write()


function createWallets(n){
    for(i=0;i<n;i++){
        console.log(`Wallet #${i+1} generated`)
        // Create wallet
        const tempWallet = web3.eth.accounts.create()
        console.log(`Address: ${tempWallet.address}\n`)
        // Add keys to JSON
        db.get('keys').push({id:db.get('count').value()+1,address:tempWallet.address, privKey:tempWallet.privateKey}).write()
        db.update('count', n => n + 1).write()
    }
}

createWallets(10)

keysDB.json

{
  "keys": [
    {
      "id": 1,
      "address": "0xD9D7e52b27CdDC12A792E621940DAB6a5EDFF3a5",
      "privKey": "0x76430d2f715a2b43eff52684089570d29b53c5e7248f0e6267b83df143f0b10b"
    },
    {
      "id": 2,
      "address": "0xB6BAd4A3F62549c35a88b6088c2c32ea1a16324B",
      "privKey": "0xe3ee3f107efecde084f4116586934bd23df90b1e6bb50aff2e98dae558091a82"
    },
    {
      "id": 3,
      "address": "0x12cFe887ee75F7adD1332FfAfe32746C5602f22e",
      "privKey": "0x0585ca813150ac5d968ce9b14b94eb01c81e46c208e437067c40fe60ccbf9f3e"
    },
    {
      "id": 4,
      "address": "0x1F08aEa7d33011Fb7e8097C5FB0aFfc0d0f588A4",
      "privKey": "0x1ed841b9c190941850036b3019c87355937529e0dade073900680bc01ef11f93"
    },
    {
      "id": 5,
      "address": "0x3875d66A26Fa374E7a1BD1A1c3d8b145C428BA62",
      "privKey": "0x45b0278d08d84f23150b1e9f8d6df8ba4c0a746fb4fd2fc4616d35d01b9851d8"
    },
    {
      "id": 6,
      "address": "0x2Ae69c9619f53f0E9eDFe5699D7f43523B638554",
      "privKey": "0xdcfaf21dfbb2fd6a8ca08fe17afc282e2058ee2a2f557c6bcfcee72556cb3dfc"
    },
    {
      "id": 7,
      "address": "0xEbeF26030a53FCbD17723a640Ce04f30e815df44",
      "privKey": "0xfde583889268cf59df96993a1a0f78c76e15df8b53732fb4222e732fac8f6712"
    },
    {
      "id": 8,
      "address": "0x358CcE6cE79D30a32A8c22bCC0cdD85C60997a47",
      "privKey": "0x5a7aa67ce8886b4e61b86ce317dbcd22a910c2da00c89ecc6357343b9ff216de"
    },
    {
      "id": 9,
      "address": "0xd948A3475fbF543D2Afe5bCc38cb1e097C8e864B",
      "privKey": "0xb522c546b91766e601afff61075e674240cfa8141b3426e48af922437ee40fc8"
    },
    {
      "id": 10,
      "address": "0xA1F384170d8708dA8Cef3cB810879A0A9159dF1f",
      "privKey": "0x0a3d200663042e873d1765250365d09065bf62ac837774ce51cb0a1f72f99c1b"
    }
  ],
  "count": 10
}